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Cochrane review of COVID-19 vaccines shows they are effective

COVID-19 vaccination

A comprehensive review of all the evidence available from randomised controlled trials of COVID 19 vaccines up to November 2021 has concluded that most protect against infection and severe or critical illness caused by the virus.

The review, a collaboration of independent, international experts, also found there was little or no difference between the number of people experiencing serious side effects after vaccination compared to those who were unvaccinated.

The researchers, led by Isabelle Boutron, Professor of Epidemiology at Universit é Paris Cité and Director of Cochrane France, analysed published data from 41 randomised controlled trials of 12 different COVID-19 vaccines, involving 433,838 people in various countries around the world. They assessed the certainty of the evidence and the risk of bias in the different studies.

The trials compared COVID-19 vaccines with placebo, no vaccine, or each other, and were published before 5 November 2021.  The vaccines investigated were: Pfizer/BioNTech, Moderna, Oxford-AstraZeneca, Bharat (Covaxin), Janssen, Sinopharm-Beijing (WIBP-CorV and BBIBP-CorV), Novavax, Coronavac-Sinovac, Soberana 2 (Finlay-FR-2), Sputnik V (Gam-COVID-Vac) and Cure Vac AG (CVnCoV).  Most trials were no longer than two months in length.

The review found that the following vaccines reduced or probably reduced the risk of COVID-19 infection compared to placebo: Pfizer/BioNTech, Moderna, CureVac COVID-19, Oxford-AstraZeneca, Janssen, Sputnik V (Gam-COVID-Vac), Sinopharm (WIBP CorV and BBIBP-CorV), Bharat (Covaxin), Novavax and Soberana 2 (Finlay-FR-2) . The following reduced or probably reduced the risk of severe or critical disease: Pfizer/BioNTech, Moderna, Janssen, Sputnik V, Bharat and Novavax. In addition, the Janssen and Soberana 2 vaccines probably decreased the risk of death from any cause. There were very few deaths recorded in all the trials and so evidence on mortality for the other vaccines is uncertain.

For most of the vaccines investigated, more people who had been vaccinated reported localised or temporary side effects compared to those who had no treatment or placebo. These included tiredness, headache, muscle pains, chills, fever and nausea. With respect to the very rare side effects associated with some vaccines such as thrombosis, the team found that the reporting of these events was inconsistent, and the number of events reported in the trials was very low.

Given the evidence of efficacy of these vaccines, the researchers question whether further placebo-controlled trials are ethical. They suggest that further research compares new vaccines with those already in use.

review of related literature about covid 19 vaccines

The current review analysed data available up to November 2021. Since then, analyses have been updated and will continue to be made publicly available every two weeks by the COVID-NMA Initiative , which provides live mapping of COVID-19 trials. A living, systematic review of clinical trials is available to researchers and policy-makers alike on the COVID-NMA platform. This enables the team to provide the most up-to-date evidence on which to base further research and decisions about prevention and treatment for COVID-19.

Prof. Boutron said:

“The evidence on COVID-19 vaccines is constantly changing and updating. Everything moves so quickly that by the time the next Cochrane review is published, or other papers are published, the data are likely to be out of date. There are more than 600 randomised trials of vaccines registered at present, and about 200 of them are recruiting. COVID-NMA is the only initiative that continues to monitor the developing evidence from trials and provides a platform for researchers to conduct their own analyses via the metaCOVID tool on the website. Researchers, clinicians and policy-makers have to take very rapid decisions about what to do to prevent and treat COVID-19. I hope that this initiative will help them to have access to the most up-to-date evidence on which to base their decisions.”
  • Read the plain language summary and full review  
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  • How to talk about vaccines when you’re not an expert: a Lifeology and Cochrane collaboration
  • Evidently Cochrane Blog : Are COVID-19 vaccines effective and safe? New Cochrane evidence

Full citation: Graña C, Ghosn L, Evrenoglou T, Jarde A, Minozzi S, Bergman H, Buckley BS, Probyn K, Villanueva G, Henschke N, Bonnet H, Assi R, Menon S, Marti M, Devane D, Mallon P, Lelievre J-D, Askie LM, Kredo T, Ferrand G, Davidson M, Riveros C, Tovey D, Meerpohl JJ, Grasselli G, Rada G, Hróbjartsson A, Ravaud P, Chaimani A, Boutron I. Efficacy and safety of COVID-19 vaccines. Cochrane Database of Systematic Reviews TBD, Issue TBD. Art. No.: CD015477. DOI: 10.1002/14651858.CD015477.

About Cochrane Cochrane is a global independent network of researchers, professionals, patients, carers, and people interested in health. Cochrane produces reviews which study all of the best available evidence generated through research and make it easier to inform decisions about health. These are called systematic reviews. Cochrane is a not-for profit organization with collaborators from more than 130 countries working together to produce credible, accessible health information that is free from commercial sponsorship and other conflicts of interest. Our work is recognized as representing an international gold standard for high quality, trusted information.  https://www.cochrane.org/

If you are a journalist or member of the press and wish to receive news alerts before their online publication or if you wish to arrange an interview with an author, please contact the Cochrane press office - [email protected]

ORIGINAL RESEARCH article

Global research on rna vaccines for covid-19 from 2019 to 2023: a bibliometric analysis.

Ziyi Chen,&#x;

  • 1 Center for Molecular Diagnosis and Precision Medicine, The First Affiliated Hospital, Jiangxi Medical College, Nanchang University, Nanchang, China
  • 2 Jiangxi Key Laboratory of Cancer Metastasis and Precision Treatment, the First Hospital of Nanchang, Nanchang, China
  • 3 Department of Pathology, Jiangxi Cancer Hospital, Nanchang, China
  • 4 Department of Pathology, Jiangxi Provincial Chest Hospital, Nanchang, China

Background: Since the global pandemic of COVID-19 has broken out, thousands of pieces of literature on COVID-19 RNA vaccines have been published in various journals. The overall measurement and analysis of RNA vaccines for COVID-19, with the help of sophisticated mathematical tools, could provide deep insights into global research performance and the collaborative architectural structure within the scientific community of COVID-19 mRNA vaccines. In this bibliometric analysis, we aim to determine the extent of the scientific output related to COVID-19 RNA vaccines between 2019 and 2023.

Methods: We applied the Bibliometrix R package for comprehensive science mapping analysis of extensive bibliographic metadata retrieved from the Web of Science Core Collection database. On January 11th, 2024, the Web of Science database was searched for COVID-19 RNA vaccine-related publications using predetermined search keywords with specific restrictions. Bradford’s law was applied to evaluate the core journals in this field. The data was analyzed with various bibliometric indicators using the Bibliometrix R package.

Results: The final analysis included 2962 publications published between 2020 and 2023 while there is no related publication in 2019. The most productive year was 2022. The most relevant leading authors in terms of publications were Ugur Sahin and Pei-Yong, Shi, who had the highest total citations in this field. The core journals were Vaccines, Frontiers in Immunology, and Viruses-Basel. The most frequently used author’s keywords were COVID-19, SARS-CoV-2, and vaccine. Recent COVID-19 RNA vaccine-related topics included mental health, COVID-19 vaccines in humans, people, and the pandemic. Harvard University was the top-ranked institution. The leading country in terms of publications, citations, corresponding author country, and international collaboration was the United States. The United States had the most robust collaboration with China.

Conclusion: The research hotspots include COVID-19 vaccines and the pandemic in people. We identified international collaboration and research expenditure strongly associated with COVID-19 vaccine research productivity. Researchers’ collaboration among developed countries should be extended to low-income countries to expand COVID-19 vaccine-related research and understanding.

Introduction

Since 2019, the global COVID-19 pandemic has affected the lives of billions of people worldwide ( 1 ). To deal with this situation, countries worldwide began to develop vaccines, including traditional inactivated vaccines, recombinant protein, live-attenuated vaccines, RNA vaccines, etc. ( 2 – 15 ). On October 2nd, 2023, the Nobel Assembly at the Karolinska Institutet decided to award the 2023 Nobel Prize in Physiology or Medicine jointly to Katalin Karikó and Drew Weissman for their discovery of nucleoside base modifications, which made it possible to develop an effective mRNA vaccine against COVID-19 ( 16 ). RNA vaccines have received widespread attention due to their high efficacy, specificity, versatility, rapid and large-scale development capabilities, low-cost production potential, and safety ( 17 , 18 ). RNA vaccines have been developed for several decades ( 19 , 20 ), and since COVID-19 has broken worldly, the RNA vaccines platform has enabled fast vaccine development in response to this pandemic ( 21 ). RNA vaccines provide flexibility in the design and expression of vaccine antigens, simulating the structure and expression of antigens during natural infections. RNA is necessary for protein synthesis and unconformity into the genome, and it is transiently expressed, metabolized, and eliminated by the body’s natural mechanism ( 22 ), so it is considered relatively safe. Many clinical trials have proven RNA-based preventive infectious disease vaccines and RNA therapeutic agents to be safe and well-tolerated ( 23 – 29 ). Generally speaking, vaccination with RNA can trigger a robust innate immune response. RNA guides the expression of vaccine antigens in host cells and has intrinsic adjuvant effects ( 30 – 32 ). One advantage of the RNA vaccine manufacturing platform is that it can quickly produce many vaccines targeting new pathogens, regardless of the encoded pathogen antigen ( 33 ). The bibliometric analysis of published articles provides insights into research prospects, gaps, and future directions in the research field. This study examined scientific publications related to RNA vaccines for COVID-19 through bibliometric analysis and trend analysis.

Search strategy

We conducted a literature search on the Web of Science Core Collection (WoSCC) database ( https://www.webofscience.com/wos/woscc/basic-search ) on January 11th, 2024. The search formula was TS= ((RNA vaccine AND COVID-19) OR (RNA vaccine AND SARS-COV-2)), the published year was set before 2024, and the type of documents was set to articles and reviews. The language filter was set in English ( Figure 1 ). According to our search strategies, there were 2962 studies of RNA vaccines for COVID-19 between 2020 and 2023 (0 publication in 2019), including 1956 articles and 1006 reviews. The analyzed publications were written by 23141 authors (93 with single-authored documents and 23048 with multi-authored documents) from 104 countries and 908 journals.

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Figure 1 Flowchart of the related data collection and bibliometrics analysis.

Characteristics of the year of publication

Figure 2A shows that the number of annual related publications increased rapidly year by year from 2020 to 2022. In 2020, 271 articles were published, while 795 in 2021, 1144 in 2022, and 752 in 2023. The most productive year was 2022 (n = 1144) with the annual scientific growth rate of 143.9%. The total number of citations per article and the average citations per year have decreased ( Figure 2B ). In 2020, the average number of citations per article was 123.5, 45.9 in 2021, 17.3 in 2022, and 2.48 in 2023. The total average number of citations per year was 24.7 in 2020, 11.5 in 2021, 5.8 in 2022, and 1.2 in 2023.

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Figure 2 (A) Annual related publication from 2019 to 2023 per year, and (B) average article and average article citations from 2019 to 2023 in COVID-19 RNA vaccine-related research. MeanTCperArt, mean total citation per article; MeanTCperYear, mean total citation per year.

Characteristics of the countries

We filtered and visualized 104 countries that published more than ten articles and constructed a collaborative network based on the number and relationship of publications in each country. From Figure 3A , we can point out that the United States has the highest literature output(n=4163) on COVID-19 RNA vaccines, and the number is significantly higher than that of China(n=1844) and Italy(n=936). Notably, there is much active cooperation between different countries. For example, the United States closely cooperates with China, the United Kingdom, Germany, and Italy; India actively cooperates with Saudi Arabia ( Figure 3B ). It shows that the United States has the most significant number of SCPs and MCPs, which indicates that the United States has the most researches on COVID-19 RNA vaccines and cooperation with other countries in this regard, followed by China on both SCP and MCP ( Figure 3C ).

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Figure 3 The geographical distribution (A) and visualization (B) of countries on the research of COVID-19 RNA vaccines. A choropleth map detailing the geographic distribution of collaborating countries. The intensity (from light blue to dark blue) is proportional to the number of publications. The number of links (presented as red lines) between any two countries represents the strength of collaboration. (C) Co-authorship analysis of countries in the related research SCP (Single country publications) indicates that the authors of this article are all from the same country, and MCP (Multiple country publications) indicates that the authors of this article are from different countries, indicating international cooperation.

Characteristics of the affiliations

In Figure 4A , Harvard University has the highest number of institutions that receive and publish articles (n=249), followed by the University of California System (n=160) and Harvard Medical School (n=76). Half the top 20 most relevant affiliations were from the United States, followed by the United Kingdom, China, France, and Israel. Subsequently, we selected 34 institutions based on visualization with a minimum number of publications equal to 5. We constructed a collaborative network based on the number of publications and relationships of each affiliation ( Figure 4B ). As shown in Figure 4B , Harvard University and Harvard Medical School cooperated the most, and Tel Aviv University and Sheba Medical Center also had active cooperation. In addition, we noticed that Harvard University had published the most papers and collaborated with the most significant number of affiliations.

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Figure 4 (A) Top 20 most relevant affiliations on the research of COVID-19 RNA vaccines. (B) Network map of co-authorship between affiliations with more than 5 citations.

Characteristics of the top 20 most productive authors

The number of academic publications by an author can represent research activities and contributions in the field to some extent. As shown in Table 1 , Ugur Sahin was the most influential author from University Medical Center, Johannes Gutenberg University, between 2020 and 2023 on COVID-19 RNA vaccines, who had published 14 articles in this field, whose h-index is 9, g-index is 14, m-index is 2.6. He also has the highest number of total citations(n=14203). Pei-Yong Shi’s h-index(n=12) is a close second. Pei-Yong Shi published 16 articles in this field between 2020 and 2023; his g-index is 16, and his m-index is 2.4. Notably, we can find that Pei-Yong Shi and Ugur Sahin had the most significant academic influence on COVID-19 RNA vaccines.

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Table 1 The author’s impact in relevant field.

Characteristics of the top 20 journals and co-cited journals

Followed by Frontiers in Immunology (n=105, 3.54%) and Viruses-Basel (n = 58, 2.94%), the Vaccines published the most articles on COVID-19 RNA vaccines (n =171, 5.77%) throughout four years. However, the New England Journal of Medicine, Nature, and Science were the most cited journals. Bradford’s law was applied to assess the core journals in the field of COVID-19 RNA vaccines. As shown in Figure 5A , the core journals in COVID-19 RNA vaccines were Vaccines, Frontiers in Immunology, Viruses-Basel, Clinical Infectious Diseases, Journal of Medical Virology, etc. As for co-cited journals in Figure 5B , journals were categorized into different clusters. The nodes with different colors in the graph represent different clusters. The node size represents the number of articles published in the journal, and the thickness of the lines represents the number of connections between nodes. Frontiers in Immunology, Vaccines, and Journal of Medical Virology were the top three most influential journals in this field. This result can help scholars to select the best-fit journals for submitting their research findings. Also, Table 2 lists the top 20 most-cited publications on COVID-19 RNA vaccines. All these productions were published between 2020 and 2023, and 65% obtained more than 1000 citations. Table 2 shows that the New England Journal of Medicine was the highest-cited journal with the highest h-index, m-index, and total citations. Frontiers in Immunology has the highest g-index. These indexes showed the importance of these two journals on COVID-19 RNA vaccines.

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Figure 5 (A) Journals (Sources) clustering through Bradford’s law. (B) Co-cited Journals of COVID-19 RNA vaccines.

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Table 2 The journal’s impact on COVID-19 RNA vaccines.

Relations between journals (left), authors (middle), and affiliations(right)

The relations between journals, authors, and affiliations were visualized using the three-field plot (TFP). In this instance, the significant features were represented in the diagram by rectangles with different colors. The height of the rectangles in the diagram of the TFP depended on the rate or value of the summation of the relations arising between the component the rectangle represents (journals, authors, and affiliations) and the diagram of other elements. The more relations the component or element had, the higher the rectangle represented. Figure 6 shows the TFP analysis of publications on COVID-19 RNA vaccines centered on relations between the journals, authors, and affiliations. The diagram demonstrated the top journals, authors, and affiliations relations in publications on COVID-19 RNA vaccines and their related studies during these four years.

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Figure 6 Three-Fields Plot revealed the relations between journals (left), authors (middle), and affiliations (right) for research in COVID-19 RNA vaccines.

Characteristics of the top 20-most cited articles and co-cited references

The top 20 most cited articles were published in 11 journals between 2020 and 2023 ( Table 3 ). Seven articles were published in The New England Journal of Medicine, and four were published in Nature. With 8609 citations, the top-cited article was published by Fernando P Polack from the New England Journal of Medicine in 2020. The total citations per year were 1721.80, and the normalized total citation was 69.69. The following one was published by Edward E Walsh and received 1574 citations, whose total citations per year was 314.80, and the normalized total citation was 12.74.

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Table 3 Main characteristics of the top 20-most cited articles.

There are 50 references of co-citation with more than five citations. As shown in Figure 7 , Wrapp d 2020 ( 34 ) has the highest number of connections with other references, followed by Hoffmann m 2020 ( 35 ). Polack fp 2020 ( 24 ) has the highest value of PageRank to get other references, which shows the importance of a node to get other nodes, followed by Baden lr 2021 ( 36 ).

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Figure 7 Network map of co-citation between references with more than five citations.

Keyword co-occurrence, clusters

Keywords are always the core research content highly condensed and summarized by researchers, which can reflect the central theme of the research. Therefore, keyword co-occurrence analysis is a crucial way to determine the main research direction and hot research topics of a specific discipline. Among Figure 8B , the most frequent author’s keywords were “covid-19” (n =1166,25%), “sars-cov-2” (n=1054,22%), “vaccine” (n=323,7%), “coronavirus” (n =183,4%), “vaccines” (n =174,4%), and “vaccination” (n = 170,4%). The overall keyword network visualization is presented in Figure 8 . It can be seen that the frequency of the words COVID-19 and SARS-COV-2 has significantly increased from 2020 to 2023.

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Figure 8 Keyword co-occurrence map (A) and the cluster of COVID-19 RNA vaccines (B) .

In this study, R studio quantitative analysis software was used to analyze the references related to the COVID-19 RNA vaccines and summarize the research results and progress. Quantitative analysis of annual publication quantity, country, author, institution, journal, and other essential information are also included. According to the number of articles published on the COVID-19 RNA vaccines in 2020, the number of documents published in this field is 271, showing an overall increasing trend. The higher the number of citations in a paper, the more excellent its impact on the field and the higher its quality. The total number of citations in this field increases between 2020 and 2022. The number of related articles in 2023 is lower than in 2022.

Through statistical analysis of the number of papers published by countries/regions and institutions, it can be determined that the key countries/regions and research institutions that have published many COVID-19 RNA vaccine literature and have a significant influence can determine their cooperation relationship. The United States and China are major countries conducting research on RNA vaccines for COVID-19, and the United States ranks first. Half of the top 20 research institutions are in the United States, followed by the United Kingdom, China, France and Israel. We noticed the close cooperation among five countries: the United States, China, the United Kingdom, Germany, and Italy. In addition, the United States has active collaborations with China, the United Kingdom, and Germany. The United States is undoubtedly the main driving force for the development of this field. The publications and cooperation between countries are significantly higher in developed countries than in developing countries. Regarding research affiliations, 50% of the top 20 most relevant affiliations were from the United States, which may be one of the essential reasons for the rapid development of the United States in this field. Regarding institutions, Harvard University is the most prolific institution, followed by the University of California System and Harvard Medical School. Affiliations like Tel Aviv University and Sheba Medical Center have an excellent cooperative relationship. Also, we found that Harvard University published the most papers and collaborated with the most institutions, which will be detrimental to the long-term development of academic research. Although some countries have cooperative relations, the frequency, breadth, and intensity of cooperation between institutions are not ideal. For example, there is only a small amount of collaboration between institutions in the United States and China. This situation will hinder the development of the research field in the long run. Therefore, we strongly recommend that research institutions in various countries carry out extensive cooperation and communication to jointly promote the development of RNA vaccines for COVID-19. Close collaboration and communication between countries and institutions are conducive to eliminating academic barriers and further developing research related to the COVID-19 RNA vaccines.

From the perspective of the author, SAHIN U, SHI PY, LIU Y, TÜRECI Ö, and LEE J published the most articles. Professor Uğur Şahin, who had the highest number of total citations, had published 14 papers, 9 of which were concerned with the immunogenicity and effectiveness of COVID-19 mRNA vaccines, and pointed out that BNT162b2 has neutralizing activity on different COVID-19 variants. They also found that BNT162B2 can elicit the response of TH1 cells and antibodies. In addition, the safety of these vaccines has also been proved ( 37 – 46 ). Pei-Yong Shi, whose h-index was second only to Uğur Şahin, has published 16 articles during these four years, most of which pointed out the safety and immunogenicity of COVID-19 RNA vaccines. These vaccines can induce the persistent response of the human germinal center. He also found that some SARS-CoV-2 variants resist these RNA vaccines ( 25 , 27 , 37 , 39 , 47 – 56 ).

Most of the research on COVID-19 RNA vaccines was published in Vaccines (IF=7.8, Q1), indicating it is currently the most productive journal in this research field. Among the journals, the journal with the highest impact factor is the New England Journal of Medicine (IF=158.5, Q1), followed by Nature (IF=64.8, Q1). As for the co-cited journals, we could find that most of them are high-impact Q1 journals. These journals are high-quality international journals providing support for the study of COVID-19 RNA vaccines.

The top 20 most cited articles were mainly published between 2020 and 2021, and all seven were published in the New England Journal of Medicine, indicating the influence of the New England Journal of Medicine in this regard. In addition, the first four articles are all about the safety and effectiveness of the COVID-19 RNA vaccines. It can be seen that the safety and effectiveness of RNA vaccines have always been a hot topic in the discussion of the COVID-19 RNA vaccines.

Vaccines, Frontiers in Immunology, and Virus Basel are the journals that publish the most articles about the COVID-19 RNA vaccines. However, regarding influence, the New England Journal of Medicine has the highest h-index, m-index, and total citations, proving that it currently has the most significant influence in this field. Frontiers in Immunology has the highest g-index, proving its importance in the field of COVID-19 RNA vaccines. Frontiers in Immunology, Vaccines, and Journal of Medical Virology were the top three most influential journals in this field, which may be listed in the journal consideration for the relevant researchers.

According to the keywords, COVID-19, SAR-COV-2, and vaccine are currently the most concerning topics conducive to further research. The research hotspots in this field mainly include COVID-19, SAR-COV-2, and vaccine. We hope this work can provide new ideas for promoting scientific research and clinical applications of COVID-19 RNA vaccines.

In general, this study is the first comprehensive analysis that summarizes the research of the COVID-19 RNA vaccines using literature metrology methods. Our research findings provide valuable information for researchers in this field to understand the basic knowledge landscape, current research hotspots, and future opportunities and identify potential collaborators in the future.

The wide application of the COVID-19 RNA vaccines provides a good platform for the development of RNA vaccine, not only contributes to the research and development of COVID-19 RNA vaccines but also proves the effectiveness and safety of RNA vaccine to a certain extent and provides sufficient theoretical and technical support for the future application of RNA vaccine in other fields, such as cancer treatment.

Limitations

Firstly, to ensure high-quality bibliometric analysis, the analysis of this study is based on articles in the Web of Science database, one of the most commonly used scientific publication databases. However, some studies may be omitted as they are published in non-SCI journals or other databases. Secondly, bibliometric analyses cannot completely replace system retrieval. Third, metrology cannot evaluate the quality of a single study because the citation index is time-dependent, meaning that recent articles may be less cited than earlier, even if they are more valuable. These limitations may slightly impact the overall results but are unlikely to alter the main trends presented in this article. In general, our research has provided a basis for understanding the research topics of the COVID-19 RNA vaccines and the production and application of the RNA vaccine.

Eligibility criteria and data source

In this study, research articles on RNA vaccines for COVID-19 published between 2020 and 2023 as original articles or reviews in English were considered eligible. Web of Science core collection database was used.

In the advanced search option of the Web of Science database, using an appropriate combination of Boolean and wildcard search operators, the following keywords were searched: “Corona Virus Disease 2019”, “COVID-19”, “RNA”, and “vaccines”. The search was performed on January 11th, 2024, and the entire search strategy is presented in TS = ((RNA vaccine AND COVID-19) OR (RNA vaccine AND SARS-COV-2, the type of documents is set to “articles” and “reviews”. The language of articles is set as English only. Then, all the resulted information, including full records and cited references, was downloaded in txt format.

Bibliometric analyses

Data management and bibliometric analyses were conducted using the Bibliometrix package (version 3.1.4) ( 57 ) and Biblioshiny ( 57 ) web apps under R (version 4.0.2). We retrieved all the main information and features included in the study. Publications and citation trends were constructed over four years. From 2020 to 2023, the most influential countries on COVID-19 RNA vaccine research were retrieved and presented as a cluster collaboration network. The cooperative world map represents world research cooperation, with the minimum edge set at 10. In addition, we identified the most productive institutions based on the highest number of paper contributions to the topic over the past four years. We used leading eigenvalue clustering algorithms to construct a collaborative network between institutions with more than five citations. We determined the author with the highest contribution based on the highest number of papers and the top 20 co-citation networks of influential authors. The 20 most cited references and the most influential journals were also identified, and some characteristics were searched, such as h-index, g-index, m-index, the total number of citations, the number of papers on the subject published in the journal, and the year when the journal began to publish COVID-19 RNA vaccine-related topics. In order to observe the inflow and outflow of journals, authors, and affiliated institutions that have contributed to the COVID-19 RNA vaccines in the past four years, a three-field plot was constructed. A tree chart was prepared to display keywords published on this topic from 2020 to 2023.

Conclusions

RNA vaccine has essential research value and application prospects in COVID-19. The rapid increase in the number of publications shows that the research on the RNA vaccine for COVID-19 has attracted more attention from scholars worldwide. The main countries are the United States and China. However, cooperation and communication between countries and institutions still need to be strengthened. On the one hand, studying the immunogenicity and safety of RNA vaccines will help us to prevent COVID-19 variants infection and reduce vaccine side effects ( 58 ). On the other hand, compared with traditional vaccines, RNA vaccines have significant advantages in preventing COVID-19. Therefore, the study of COVID-19 RNA vaccines has essential application value in preventing COVID-19 infection and alleviating symptoms in the future ( 59 ). In addition to the related prevention research of COVID-19, attention can also be paid to the transformation of research achievements, that is, the clinical application of RNA vaccines in other diseases ( 58 ).

Data availability statement

The original contributions presented in the study are included in the article/supplementary material. Further inquiries can be directed to the corresponding authors.

Author contributions

ZC: Conceptualization, Visualization, Writing – original draft. ZL: Software, Validation, Writing – review & editing. YF: Writing – review & editing. AS: Writing – original draft. LW: Writing – review & editing. YS: Conceptualization, Funding acquisition, Supervision, Writing – original draft. CL: Conceptualization, Software, Supervision, Writing – original draft, Writing – review & editing.

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This study was supported by the Jiangxi Provincial Natural Science Foundation of China (20204BCJL23052, 20212ACB216013) and by Nanchang Natural Science Foundation No.129 in 2021.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

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Keywords: COVID-19, SARS-CoV-2, RNA vaccines, web of science, bibliometrics

Citation: Chen Z, Liu Z, Feng Y, Shi A, Wu L, Sang Y and Li C (2024) Global research on RNA vaccines for COVID-19 from 2019 to 2023: a bibliometric analysis. Front. Immunol. 15:1259788. doi: 10.3389/fimmu.2024.1259788

Received: 16 July 2023; Accepted: 01 February 2024; Published: 15 February 2024.

Reviewed by:

Copyright © 2024 Chen, Liu, Feng, Shi, Wu, Sang and Li. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Yi Sang, [email protected] ; Chenxi Li, [email protected]

† These authors have contributed equally to this work

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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  • Published: 07 February 2024

Understanding the role of risk preferences and perceptions in vaccination decisions and post-vaccination behaviors among U.S. households

  • Jianhui Liu 1 ,
  • Bachir Kassas 2 ,
  • John Lai 3 ,
  • Jaclyn Kropp 4 &
  • Zhifeng Gao 5  

Scientific Reports volume  14 , Article number:  3190 ( 2024 ) Cite this article

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  • Health care
  • Risk factors

COVID-19 vaccines play a critical role in protecting against infection and transmission of the virus. Therefore, understanding public perceptions of COVID-19 vaccines is essential for successful vaccine promotion. Previous literature reported strong associations between vaccination decisions and several sociodemographic variables. However, knowledge about how behavioral factors, including risk perceptions and preferences, impact individuals’ attitudes towards receiving COVID-19 vaccination is currently lacking. Using data from a nationally representative survey of 1050 US adults, this study investigates the correlation between individuals’ decisions to receive COVID-19 vaccination and both their risk perceptions and preferences. Additionally, we investigate post-vaccination behavior by measuring individuals’ participation in three different groups of activities that vary by their degree of social exposure. We find strong correlations between vaccination decisions and four measures of risk preference and risk perception. We also find associations between the four risk measures and individuals’ behaviors post-vaccination. We shed light on the main factors discouraging the uptake of COVID-19 vaccines, as well as public opinions regarding the performance of different organizations in addressing the COVID-19 pandemic, and grocery store policies to prevent COVID-19 infections. Our study provides critical information that can help policymakers communicate more effectively with the public and promote vaccine uptake among population groups and geographic areas with higher anti-vaccine sentiments.

Introduction

Following the World Health Organization’s (WHO) declaration of COVID-19 as a global pandemic 1 , worldwide efforts were mobilized to limit the transmission and public health impacts of COVID-19. Initial prevention measures, including lockdowns and other mitigation behaviors (e.g., social distancing, face masks, and sanitation), succeeded in slowing the transmission of the virus 2 . However, the sustainability of these methods is not pragmatic due to adverse effects on the economy and global supply chains. More enduring solutions that have emerged included the use of COVID-19 vaccines. In the United States (US), the Food and Drug Administration (FDA) issued emergency use authorization for two COVID-19 vaccines, Pfizer-BioNTech and Moderna, in December 2020. This was followed by a third vaccine by Johnson and Johnson, which was approved in February 2021. Extensive research on these vaccines showed decreased transmission rates, along with reduced severity of COVID-19 symptoms 3 .

Vaccination treatments have been deployed in human populations for centuries to prevent the spread of various transmissible diseases, such as Influenza, tuberculosis, and pertussis 4 . However, compared to regular seasonal Influenza, and other previous global pandemics, such as the 2009 H1N1 Influenza, COVID-19 carries more severe symptoms and much higher infection and mortality rates 5 . COVID-19 vaccines have proven to be crucial tools for protecting public health 6 . Despite the effectiveness of COVID-19 vaccines in preventing severe symptoms, many people remain unvaccinated 7 . Thus, it is important to promote the uptake of COVID-19 vaccines among US households, especially during periods of high transmissibility and infection rates 3 .

Immunization programs are not considered successful until high crowd acceptance and high inoculation rates are achieved 8 , leading to what is commonly referred to as “herd immunity”. Reaching herd immunity depends on the decisions and behaviors of the population. As more people get vaccinated, the potential for reaching herd immunity increases, and mutated virulent strains or variants may become less likely to emerge 9 . Furthermore, achieving herd immunity could be expedited by increasing the pace of vaccination and reducing vaccine hesitancy 10 . For this reason, it is critical to understand public perceptions and acceptance of COVID-19 vaccination. This knowledge is extremely helpful in informing the development of effective strategies to encourage higher vaccine acceptance and uptake. In this study, we investigate behavioral characteristics influencing COVID-19 vaccination decisions. Specifically, we focus on how individuals’ risk perceptions and risk preferences correlate with their attitudes toward COVID-19 vaccination. We also analyze the main factors discouraging COVID-19 vaccination and examine changes in behavior post-vaccination.

Vaccine hesitancy can be defined as voluntary refusal or delay in accepting available vaccine, and it is driven by many context-specific factors that vary across location, time, and type of vaccine 11 , 12 . During the development period of COVID-19 vaccines, several researchers found that requests for such vaccines were strongly correlated with multiple demographic factors, such as gender, race, education, political affiliation, and household characteristics 13 , 14 , 15 , 16 . Conversely, some individuals rejected vaccinations for reasons that included concerns about side effects, general distrust in all vaccines, and over-confidence about their own health conditions 17 , 18 , 19 , 20 . We contribute to this literature by examining how individuals’ risk perceptions and preferences correlate with their vaccination decisions, and by investigating vaccination plans for individuals who have not yet received the COVID-19 vaccine.

An individual’s risk perception can be defined as an intuitive assessment of losses and/or hazards relating to a specific action or situation 21 . This judgment process comprises the individual’s perception of the likelihood of a hazardous event and how the individual labels a situation in terms of the risk level (e.g., low/high risk) 22 . On the other hand, risk preferences define people’s consistent tendency or inclination toward risk in their decision-making process 23 . Risk perceptions and preferences are both important determinants of individual behavior under risk 24 . Thus, in this paper, we use four different risk measures to examine how risk perceptions and risk preferences correlate with COVID-19 vaccination decisions.

Our study presents several important contributions. First, it builds on existing literature by examining sociodemographic and behavioral factors influencing COVID-19 vaccination decisions in the US. Existing studies showed significant correlations between vaccination decisions and several sociodemographic factors, including race, gender, and employment status 8 , 16 . Behavioral factors, such as online misinformation, false claims, and conspiracy theories about the COVID-19 vaccine, were also shown to significantly influence the acceptance of vaccination 25 , 26 . Another study found that in Portugal, delays in COVID-19 vaccination, and refusal of vaccination, were highly associated with people’s age, income loss due to the pandemic, and intention to take the flu shot 27 . However, little is known about the extent to which risk perceptions and risk preferences influence individuals’ choices to receive the COVID-19 vaccine, although these risk measures were shown to be highly correlated with other health-related behaviors 23 , 28 , 29 . Our study highlights how several factors, including risk perceptions and risk preferences, lead to divergent COVID-19 vaccine sentiments among individuals in the US.

Second, this study contributes to the limited literature investigating changes in people’s daily activities post-vaccination. While Gaube et al. 57 showed evidence that behaviors specific to health and safety are highly associated with risk perceptions, the effects on other regular daily activities are still ambiguous. Several studies showed that participation in physical activities, and other health-promoting behaviors, have significantly changed as a result of the pandemic 30 , 31 , 32 , 33 . However, little is known about how participation, or anticipated participation, in other daily activities, such as dining out and recreational behaviors, changed during the pandemic, and how COVID-19 vaccination influences participation in these activities. Our study adds to this literature by investigating these correlations.

Third, our study contributes to the growing literature on public attitudes related to food retail store policies during the COVID-19 pandemic, which are important considerations for a more comprehensive understanding of public health responses to potential future disease outbreaks (e.g., new variants of COVID-19 or future epidemics/pandemics). The pandemic imposed short-term and long-term challenges on the food retail industry, resulting in a significant shift in consumer indoor shopping behavior 34 . To reduce the spread of the virus, many stores implemented risk-mitigating policies to create a safer shopping environment for their customers. Since a satisfactory shopping experience is crucial to maintaining long-term profitability in the contemporary retailing industry 35 , it is important to consider public opinions toward these store policies. Understanding these opinions helps cultivate an environment that matches consumer preferences and needs, while ensuring proper measures are taken to promote public safety 25 , 36 , 37 . However, research on individual perspectives on risk-mitigation policies in food retail stores is limited. This study helps improve the understanding of public opinions regarding COVID-19-related policies in US food retail stores.

Forth, our study contributes to the literature investigating the level of public trust in governments and public health officials during the pandemic. Higher level of confidence in the government can enhance individuals’ resilience to adapt and recover from epidemics and pandemics 38 . Efficient government communication is challenging, yet essential for raising awareness and promoting risk-mitigating behaviors during global health crises. Alders and Bagnol 58 showed that effective communication was a crucial element in the prevention and control strategy targeted toward the Highly Pathogenic Avian Influenza (HPAI), which is another deadly and highly infectious respiratory virus commonly referred to as the “bird flu”. It is therefore crucial to understand the level of public trust in these entities to increase compliance levels and enhance communication strategies. However, it is not surprising to expect individuals to have divergent attitudes and levels of trust toward different groups/organizations—such as the World Health Organization (WHO), Centers for Disease Control and Prevention (CDC), and US government—especially during global pandemics like COVID-19. Two separate studies by Soares et al. 27 and Latkin et al. 7 found that individuals with stronger opposition to the vaccine generally hold more negative perceptions and lower levels of trust in the CDC. Our study provides insights regarding the disparate public perspectives on the COVID-19-related performance of different organizations/groups to help governments achieve efficient communications with the public.

Materials and methods

An online survey was conducted between June 25 and August 24, 2021, to collect data from a nationally representative sample of 1050 US adults (ages 18 and above). Proportional representation was achieved based on age, gender, income, and region (Northeast, Midwest, West, South). To ensure data quality, attention check questions were included in the questionnaire to filter out subjects who were not paying close attention to the questions 39 . In addition, the survey was limited to 15–20 min in length to avoid respondent fatigue. A copy of the survey instrument is provided in the appendix.

Vaccination behaviors and reasons

The survey collected information related to the respondents’ vaccination behaviors. Respondents reported whether they had received at least one dose of any COVID-19 vaccine (i.e., Pfizer, Moderna, Johnson and Johnson, etc.). For unvaccinated respondents, follow-up questions were asked about future vaccination plans (i.e., whether or not they plan to get vaccinated at some point or if they are unsure). We used these responses as one of our primary outcome variables to investigate how behavioral and sociodemographic characteristics correlate with people’s vaccination decisions.

To better understand people’s vaccination hesitancy, those who indicated an unwillingness to get vaccinated were asked to specify the primary reasons for this decision, and the importance (on a scale of 0–100) of each reason, out of a total of 20 possible reasons, which included “I am concerned about negative side effects of the vaccine” , “I don’t believe the vaccine is safe” , “I don’t believe the vaccine is effective” , “I don’t trust vaccines in general” , and “I am taking enough precautionary measures to avoid contracting COVID-19” . The full list of vaccination-discouraging reasons used is included in Fig.  3 , which is discussed in the Results section.

Respondents were also asked to report changes in their participation in 15 daily activities post-vaccination (or expected changes for unvaccinated respondents). The activities included indoor dining, outdoor dining, restaurant food pickup, restaurant food delivery, going out to bars, grocery store visits, online shopping, movie theatres, sports games, theme parks, outdoor recreation, and air travel. The respondents’ reported changes in participation in these 15 activities were then analyzed to determine factors affecting post-vaccination (anticipated) behaviors.

Public attitudes toward store policies and levels of trust in organizations

To better understand people’s views about retail store policies and trust in different information sources, we asked respondents to indicate their level of agreement, on a Likert scale from 1 (“strongly disagree”) to 5 (“strongly agree”), with a set of 10 different grocery store policies related to COVID-19. These statements included “grocery stores should follow CDC guidelines” , “the store should wipe down shopping carts” , “shoppers should maintain 6 feet of distance” , “physical barriers should be used between cashiers and customers” , and “masks should be worn by all customers” . The full list is included in Fig.  5 and discussed in the Results section. Further, the survey collected respondents’ perspectives on the pandemic-related performance of different organizations—namely the WHO, foreign governments, the US government, the CDC, state health departments, local county health departments, primary care physicians, and pharmacists. Respondents indicated their evaluation of how well each entity handled the COVID-19 pandemic on a scale ranging from 1 (“not well at all”) to 5 (“extremely well”).

Risk measurements

Four risk measures were used to elicit respondents’ risk preferences and risk perceptions, which serve as explanatory variables in our analysis. Individual risk perceptions can be measured by collecting respondents’ views of the risk involved in different risky activities 40 . Based on an approach by Lusk and Coble 56 , we measured risk perceptions related to the pandemic by collecting respondents’ perceptions of the likelihood of exposure to COVID-19 in 14 different locations/activities: grocery store, hospital/clinic, doctor’s office, delivered packages, restaurant/bar, gas station, work, home, outdoor recreation, religious gathering, public transit, taxi/ride-share, daycare, and school. Respondents reported their perceived likelihood of contracting COVID-19 in each location/activity on a Likert scale ranging from 1 (“extremely unlikely”) to 5 (“extremely likely”). We then summed the number of places where each respondent perceived the likelihood of exposure to COVID-19 as “somewhat likely” or “ extremely likely ” to construct the Number of Risky Places (NRP) as our first risk measure.

A more direct way of eliciting individuals’ risk perceptions related to COVID-19 is to ask respondents about their perceived probability of contracting the virus. Respondents reported on a scale from 0 to 100% their perceived likelihood that they, or someone in their household, would contract COVID-19 in 2021, which we used as the second risk measure. This measure was labeled Perceived Probability of Contracting COVID-19 (PPCOV). This risk measure is crucial given the rapidly evolving nature of the disease, the repeated COVID-19 infections among some individuals, and the assumption that respondents’ risk-related behaviors are more likely to be driven by their own subjective perceptions rather than the objective probability of contracting COVID-19.

Following the 11-point Likert scale used in the German Socio-Economic Panel (SOEP) survey 41 , a proper way to measure risk preferences is to ask participants to assess and rank their own behaviors on a continuum ranging from risk-averse to risk-loving. This approach has also been used to elicit individual risk preferences in health-related decision-making 42 . We used a generic 11-point Likert scale, ranging from 0 (“extremely risk averse”) to 10 (“extremely risk loving”), and asked respondents to identify themselves on this scale. This was taken as our third risk measure, labeled Self-Assessed Risk Aversion (SARA). This risk measure is considered adequate since it is easy for subjects to understand and follow. Also, its domain-general nature addresses the fact that the impacts of COVID-19 do not easily fit into a single domain-specific category.

The fourth risk measure used in this study elicited the number of COVID-19 mitigation behaviors, out of a total of 7, that respondents were practicing. These behaviors included maintaining physical distancing, reducing non-essential trips away from home, washing hands more frequently, wearing a mask when away from home, wearing gloves when away from home, using delivery services, and additional household cleaning/sanitation. The total number of mitigation behaviors was summed for each respondent to create the fourth risk measure, which is labeled sum of mitigation behaviors (SMB).

COVID-19-related household information

In addition to the respondents’ sociodemographic characteristics, the survey collected COVID-19-related household information, such as the presence of immunocompromised family members and the presence of family members working in healthcare and other essential industries. Information about the respondents’ exposure to COVID-19 was also collected, namely, whether they tested positive for the virus, self-isolated, or were hospitalized due to COVID-19. The survey also elicited respondents’ outlook on COVID-19 and the economy by asking the dates (month and year) when they believed the pandemic would end and the economy would return to normal. The description of all the variables collected in our study are summarized in Table 1 .

Ethical approval

This study was approved by the Institutional Review Board of the University of Florida. Informed consent was obtained from all subjects who participated in this study. All methods were carried out in accordance with relevant guidelines and regulations.

Descriptive statistics

The demographic and behavioral characteristics of the respondents are summarized in Table 2 . Approximately, 51% of respondents are male, and the average household size pre-COVID-19 was between 2 and 3 members, with approximately 32% having children under 18 years old and 36% having senior family members. About 27% of the respondents self-identified as Republican, 39% as Democrats, and the rest as independent/other.

Approximately 72% of the respondents claimed that they or their spouse had received at least one dose of any brand of the COVID-19 vaccine. Among unvaccinated respondents, 25% (7% of total sample) reported an intention to get vaccinated in the future, 29% (8% of total sample) were unsure whether or not they would want to receive the vaccine, and the remaining 46% of the unvaccinated respondents (13% of total sample) indicated a preference against being vaccinated. Regarding other health-related variables, 18% of the respondents reported having immunocompromised members in their household, while only 4% had pregnant household members. About one-third of the respondents reported household members employed in essential industries, and 27% reported a reduction in their household income level due to COVID-19.

With regard to the risk measures, we find that the average SARA was 4.73 out of 10, which indicates slight risk aversion. On the other hand, the mean NRP was only 3.87, implying that respondents only perceived a positive risk in an average of 4 out of 14 places/activities. The average PPCOV for the sample was approximately 21%. A correlation matrix is included in the online appendix to examine potential multicollinearity issues between our risk measures. Based on the calculated Variance Inflation Factors (VIFs), which were all quite low, we find no evidence of significant multicollinearity between any of our measures.

Since these risk measures would most likely differ with respondents’ vaccination decisions and plans, bar graphs of SARA, NRP, and PPCOV of respondents with different vaccination decisions/plans are shown in Fig.  1 . Among all the unvaccinated respondents, those who reported an intention to get vaccinated in the future have the highest mean value of SARA (5.81), indicating that they were more willing to take risks than individuals who do not intend to get vaccinated or who are unsure. This might imply that a majority of unvaccinated respondents view getting vaccinated as a risky behavior, which could explain the lack of intent to get vaccinated in order to avoid potential risks associated with the vaccine. Vaccinated respondents, on the other hand, were the most risk-averse group among all. This may be caused by the fact that they perceived COVID-19 as riskier than the vaccine. The group of respondents who were unvaccinated and not planning to get vaccinated had a mean NRP value of 2.53 and thus perceived the least number of places as risky. Those who were unvaccinated but planning to get vaccinated perceived the highest number of risky places, with a mean NRP of 5.98. In terms of PPCOV, unvaccinated individuals who had the intention to receive the vaccine in the future reported the highest level of PPCOV (32%). The average PPCOV of vaccinated individuals was 21%. It is highly probable that these individuals believe that getting vaccinated was effective, and it significantly decreased their perceived probability of contracting COVID-19. Unvaccinated individuals who did not intend to receive the vaccine had the lowest level of PPCOV (19.71) among all groups of respondents.

figure 1

Histograms for Risk Measures. ( a ) Self-Assessed Risk Aversion (SARA); ( b ) Number of Risky Places (NRP); (3) Perceived Probability of Contracting COVID-19 (PPCOV).

Figure  2 presents the fraction of respondents following each of seven COVID-19 risk-mitigation behaviors, along with a breakdown of SMB by respondents’ vaccination decisions or plans. The mean value of SMB was 3.97 out of 7. We observe that most people were practicing frequent hand washing (83%), wearing a mask away from home (78%), and maintaining social distancing (70%). Conversely, the least practiced risk-mitigation behavior related to COVID-19 was “wearing gloves away from home”. Unvaccinated individuals who reported an intention to get vaccinated in the future had the highest value of SMB (4.91) among all groups of respondents, followed by the vaccinated group (4.11). Individuals who were unvaccinated and did not plan to get vaccinated reported practicing the fewest risk-mitigating behaviors (2.89).

figure 2

Participation in Risk Mitigation Behaviors. ( a ) Fraction participating in each risk mitigation behavior; ( b ) histogram for Sum of Mitigation Behaviors (SMB).

Analyzing vaccination behaviors

Figure  3 presents a summary of the reasons why respondents choose not to receive COVID-19 vaccines, as well as the perceived importance of each reason. The most common reason was concern about the potential side effects of the COVID-19 vaccines, which was selected by approximately 65% of respondents. This was followed by the safety concern, where 43% reported that they do not believe the vaccine is safe. Approximately 26% of the unvaccinated group doubted the effectiveness of the COVID-19 vaccine, another 26% did not trust any vaccine in general, and about 25% believed they were taking enough precautionary measures. The least chosen reasons for not receiving the COVID-19 vaccines were “the vaccine is unavailable,” “I am unable to get an appointment,” and “the vaccine site is too far” (Fig.  3 a). With an average perceived importance score of 84 out of 100, concern about the safety was perceived as the most important reason for not receiving the COVID-19 vaccines (Fig.  3 b). The second and third most important reasons were concerns about side effects and confidence in one’s health condition, with scores of 83 and 79, respectively. Reasons related to the availability and convenience of obtaining the COVID-19 vaccines received the lowest importance ratings by the respondents.

figure 3

Reasons for not receiving COVID-19 vaccination. ( a ) fraction of respondents selecting each reason. ( b ) average importance of each reason for respondents.

Two separate regressions were used to investigate factors associated with vaccination decisions. The first regression was a Logistic model over the full sample, with an indicator outcome variable that took the value 1 for vaccinated and 0 for unvaccinated. The second regression was estimated using the unvaccinated subsample, where we coded unvaccinated respondents with a 3-level outcome variable that took the value 0 if the respondent had no intention of being vaccinated, 1 if they were unsure, and 2 if they planned to be vaccinated in the future. Since the outcome variable is ordered in an increasing tendency toward vaccination, we estimated an ordered Logit model over the unvaccinated subgroup. This allows us to assess how different factors correlate with both current and future vaccination plans.

Table 3 presents the results of both regression models.We also use the unvaccinated subsample to estimate a multinomial logit model. The results are presented in Appendix A. In the logistic model, we observe that individuals who follow more COVID-19-related risk mitigation behaviors are more likely to be vaccinated. Not surprisingly, SARA was negatively correlated with people’s vaccination decisions, indicating that a more risk-averse person (i.e., lower SARA) was more likely to get the vaccine. PPCOV was also negatively associated with respondents’ vaccination decisions, which implies a higher likelihood of being vaccinated for individuals with a lower perceived probability of contracting COVID-19. Having self-isolated also increased the likelihood of getting the vaccine, while being optimistic about economic recovery post-COVID-19 had an opposite effect.

Regarding other highly significant demographic variables, having children in the household decreased the likelihood of getting the vaccine, whereas the presence of senior or immunocompromised household members increased the probability of getting the vaccine. We also find lower vaccination likelihood among respondents identifying as Republicans compared to other political groups. On the other hand, respondents who were married, older, and/or more educated had a significantly higher likelihood of being vaccinated. Compared to other ethnicities, results also imply that being either White, Asian, or Hispanic American significantly increased the likelihood of receiving the COVID-19 vaccine.

With respect to the ordered logit model over the unvaccinated subsample, our results consistently show a positive correlation with SMB, indicating that, among unvaccinated individuals, those practicing more mitigation behaviors have higher intentions to get vaccinated in the future. NRP was also highly associated with respondents’ vaccination plans, suggesting that respondents identifying a positive risk of COVID-19 infections in a larger number of places are more inclined toward planning to receive COVID-19 vaccination. Other risk measures investigated (i.e., PPCOV and SARA) were not significantly correlated with respondents’ plans to receive COVID-19 vaccination. Notably, we find a negative association between having senior household members and planning future COVID-19 vaccination among unvaccinated respondents, which is contrary to the result in the Logit model using the full sample. This implies that, although having senior household members increased the likelihood of receiving COVID-19 vaccination, individuals who were not yet vaccinated were less likely to plan to do so if they had senior members in the household. The role of political affiliation and age on vaccination plans was consistent with the sign of their correlation with vaccination decisions. Specifically, self-identified Republicans and younger individuals are less likely to plan COVID-19 vaccination. Finally, respondents with higher income levels had a higher likelihood of planning to get vaccinated.

Analyzing changes in activities post-vaccination

Changes in the level of participation in various activities for vaccinated respondents after receiving their vaccinations, and the anticipated changes for unvaccinated individuals, are summarized in Fig.  4 . Values that are greater than 0 indicate an increase in the level of participation in a particular activity, and vice versa. Unvaccinated respondents reported higher engagement in almost all categories of activities compared to vaccinated respondents. On average, vaccinated individuals reported the highest increase in indoor dining, online shopping, and grocery store visits post-vaccination. On the other hand, unvaccinated respondents anticipated the highest increase in online shopping, restaurant food delivery, indoor dining, and socializing with friends upon vaccination. Notably, vaccinated respondents reported a decrease in their participation in organized sport games, indoor public events, movie theatres, air travel, and theme parks post-vaccination. In contrast, unvaccinated respondents did not report a decrease in participation in any of the 15 activities listed. One possible explanation for this could be the fact that vaccinated individuals are the most risk-averse group among all other groups of respondents, as presented earlier in Fig.  1 a.

figure 4

Changes in the level of participation of vaccinated and unvaccinated individuals.

To further investigate factors that are correlated with (anticipated) changes in participation in the 15 activities/places, we first conducted a Principal Component Analysis (PCA) as a method to reduce the dimensionality of the data while preserving the majority of observed variation 43 . Using this data reduction technique, a series of factors can be described by fewer inter-correlated quantitative variables (i.e., linear combinations of these factors of interest) to facilitate data analysis. Due to the fact that many of the 15 factors are moderately or highly correlated, we did not choose to perform a Cluster Analysis (CA) since CA will generally be outperformed by PCA in cases where the variables of interest are highly correlated 44 . To test the suitability of PCA, we performed 3 different tests, namely Kaiser–Meyer–Olkin (KMO) Test, Bartlett’s Test of Sphericity, and the Cronbach’s Alpha Test. We obtained an overall score of 0.9236 for the KMO Test, implying a high sampling adequacy level 45 . Bartlett’s Test of Sphericity also showed high significance with a p -value of 0.000 45 . The scale reliability coefficient obtained from Cronbach’s Alpha Test was 0.893, which indicated a high level of internal consistency in our sample data 46 . Thus, we concluded that the PCA was appropriate for our analysis.

Three principal components were found to be the best fit, explaining approximately 63.57% of the variability in the data. Factor loadings of each principal component on the activities are reported in Table 4 . The first component, defined as “high social-exposure activities” (HSA), included going to bars, movie theatres, organized sports games, theme parks, air travel, indoor public events, and outdoor public events. These activities are generally perceived as highly risky since they involve interacting with a large number of individuals. Also, many of these were recreational activities that could be considered unnecessary (compared to other essential daily activities), and the pandemic was negatively impacting their corresponding industries. The second component was labeled “medium social-exposure activities” (MSA) and comprised indoor dining, outdoor dining, grocery store visits, and socializing with close friends. These activities required people to interact with relatively smaller crowds and could thus be considered intermediate in risk level. The third component, labeled “low social-exposure activities” (LSA), included restaurant food pickup, restaurant food delivery, and online shopping. This category of activities required minimum contact with other people and could thus be considered low risk.

Separate regressions were estimated using the three components from PCA as outcome variables, as presented in Table 5 . The same covariates from Table 3 were included in these regressions. Regression results indicated that vaccinated respondents were more prone to engage in MSA. Planning to receive the vaccine in the future resulted in a higher level of participation in LSA. We also find that respondents following a higher number of COVID-19 risk-mitigation behaviors decrease their participation in HSA and MSA activities. Furthermore, results suggested a highly positive correlation between NRP and engagement in activities from all three categories. The positive coefficients on SARA implied that risk-loving respondents tend to participate more in both HSA and LSA. We also observed that a higher PPCOV was associated with an increase in participation in LSA.

Regarding other control variables, having self-isolated increased respondents’ participation in HSA post-vaccination. However, participants who tested positive were more prone to engage in LSA. Unsurprisingly, results also suggested that respondents who are more optimistic about economic recovery increased their participation in LSA. In addition, having pregnant members or children in the household increased engagement in LSA, while the presence of seniors or members in the healthcare industry decreased engagement in LSA. Results also suggest that respondents with higher education levels were more likely to participate in LSA, while higher income respondents were more likely to engage in MSA. Finally, Hispanic participants were less likely to engage in both HSA and MSA.

Analyzing public opinions towards grocery store policies and public health safety efforts of different organizations

Given the respondents’ reported increase in grocery store visits, and their participation in risk-mitigation behaviors, it is crucial to understand their opinions on various store policies to mitigate the transmission of COVID-19 infections. The participants’ average agreement with various grocery store policies was coded in a 5-point Likert scale, ranging from − 2 (strongly disagree) to 2 (strongly agree). Results are presented in Fig.  5 . Notably, the vaccinated group reported higher agreement with all store policies compared to unvaccinated respondents. The highest level of agreement was given to “Grocery stores should follow CDC recommendations”, “The store should wipe shopping carts”, and “Shoppers should maintain 6 feet of distance”. While most store policies received positive feedback from the respondents, both the vaccinated and unvaccinated groups opposed the requirement of mandatory glove-wearing by all customers. Further, the unvaccinated group disagreed that “There should be special access hours for people who are vaccinated” and that “Aisles should be one-way travel”. These results further confirm that vaccination does not make respondents open to more risky activities. Instead, it is highly probably that risk preference is what drives individuals’ risk behaviors and attitudes toward grocery store policies.

figure 5

Level of agreement on store policies.

Respondents’ perspectives on how well different organizations handled public health safety efforts related to COVID-19 were coded in a 5-point Likert scale ranging from 1 (not well at all) to 5 (extremely well). Results are summarized in Fig.  6 . We find that vaccinated individuals gave a higher assessment of all the groups/organizations, on average, compared to unvaccinated respondents. Among all the organizations, primary care physicians and pharmacists were highly recognized by both vaccinated and unvaccinated respondents for their efforts related to the COVID-19 pandemic. Further, both groups of respondents gave the lowest ratings to the US and Foreign governments.

figure 6

Rating how well each group handled public health safety efforts related to COVID-19.

Discussion and conclusion

The COVID-19 pandemic had a negative impact on the world, not only because of COVID-19’s high transmission, infection, and mortality rates when compared to previous respiratory diseases, but also because of the social consequences, such as economic loss due to limited operations or even closure of many businesses, involuntary unemployment, and high public health expenses 47 , 48 , 49 . Thus, it is crucial to investigate individuals’ vaccine-related behaviors to provide useful insights for public health policies to achieve higher compliance and further promote vaccine confidence among the US population to establish herd immunity and prevent further economic losses.

In this study, we investigated primary factors influencing people’s vaccination decisions to better understand their vaccine hesitancy. We customized four different risk measures relating to both risk perceptions and risk preferences and analyzed their relative correlation with respondents’ vaccination decisions. Results indicate that all four risk measures were highly associated with respondents’ vaccination behaviors, and vaccination plans for unvaccinated individuals. In addition to the risk measures, our study conforms to previous findings that reported significant associations between sociodemographic variables, such as race, age, political affiliation, education, and income level, and individuals’ vaccination behaviors 15 , 16 , 27 , 50 , 51 . However, unlike previous studies by Akarsu et al. 13 , Troiano and Nardi 51 , and Soares et al. 27 , our results suggest that gender, working status, and experiencing income loss due to the pandemic do not significantly influence the decision to get vaccinated.

When looking at the main reasons why unvaccinated individuals are reluctant to get vaccinated, we discover that a majority were highly concerned about side effects, effectiveness, and safety of the vaccine, which is consistent with previous findings 13 , 18 , 19 , 26 , 27 . Some respondents were overly optimistic about their personal health conditions or mistrusted vaccines in general. More importantly, our results suggest that for a vast majority of individuals, it is not convenience or availability that is stopping them from getting vaccinated. Instead, anti-vaccine sentiments seem to be the most crucial reason. This implies that rather than putting more effort into increasing the availability of the vaccine, efforts should be directed at informational and promotional campaigns to encourage higher vaccine trust and acceptance. These results can help guide policymakers in promoting higher vaccine uptake, not only specific to COVID-19, but also for the vaccines created for other infectious diseases. Specifically, our results highlight the importance of assuring vaccine effectiveness and addressing public concerns over vaccine safety and potential side effects. In addition, policymakers can use these findings to tailor their promotional campaigns to specific groups of people who were shown to carry stronger anti-vaccine sentiments.

The COVID-19 pandemic reshaped people’s lifestyles and their level of participation in several daily activities. The significant correlations we highlight between our risk measures and three groups of activities with different levels of social exposure provide useful implications for understanding people’s behavioral changes post-vaccination. All of the four risk measures were strongly associated with at least one of the social-exposure activities. In addition, vaccinated respondents were more prone to participate in MSA. Self-isolating or testing positive for COVID-19, optimism about economic recovery, presence of special household members (i.e., pregnant, immunocompromised, etc.), education level, and ethnicity were all significant determinants of respondents’ level of participation in different activities post-vaccination. This information is useful in guiding policymakers to effectively focus efforts on regulating high social exposure activities among groups with a higher participation likelihood to prevent further outbreaks of infections in the future. Our results also suggested that policymakers and state health departments can perform preventive health regulation by focusing on the activities/locations with high participation levels, not specific to COVID-19, but also in any future events of pandemics. These could include limiting the total number of people in a restaurant or grocery store, mandating mask wearing, and requiring negative test results, which were implemented in a majority of states/territories during the early months of the pandemic 52 , 53 , 54 , 55 .

Lastly, this study expands on the literature on public opinions by investigating the level of agreement with several grocery store policies, as well as levels of trust in different groups/organizations. Since both reducing the spread of the virus and ensuring customer satisfaction are highly important, the public’s perspectives on store risk-mitigation policies can help grocery stores, and other retail industries, to adjust their procedures and services to achieve higher customer satisfaction while maintaining a safe shopping environment. Furthermore, our study shows that primary care physicians and pharmacists received the highest rating and level of trust compared to other organizations/groups. At the same time, the US and foreign governments were least appreciated in terms of their health-related efforts during the pandemic. These findings provide insights regarding the disparate public opinions to help governments achieve efficient communications with the public to better address COVID-19 and other future public health challenges.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author upon request.

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B.K., J.L., J.K., and Z.G., contributed to the study conceptualization, study design, and data collection. Data analysis was led by J.L., B.K., and J.L. The first draft of the manuscript was written by Jianhui Liu, and all authors contributed to revising and finalizing the manuscript.

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Liu, J., Kassas, B., Lai, J. et al. Understanding the role of risk preferences and perceptions in vaccination decisions and post-vaccination behaviors among U.S. households. Sci Rep 14 , 3190 (2024). https://doi.org/10.1038/s41598-024-52408-6

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review of related literature about covid 19 vaccines

A Narrative Review of COVID-19 Vaccines

Affiliation.

  • 1 Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, Sydney 2006, Australia.
  • PMID: 35062723
  • PMCID: PMC8779282
  • DOI: 10.3390/vaccines10010062

The COVID-19 pandemic has shaken the world since early 2020 and its health, social, economic, and societal negative impacts at the global scale have been catastrophic. Since the early days of the pandemic, development of safe and effective vaccines was judged to be the best possible tool to minimize the effects of this pandemic. Drastic public health measures were put into place to stop the spread of the virus, with the hope that vaccines would be available soon. Thanks to the extraordinary commitments of many organizations and individuals from around the globe and the collaborative effort of many international scientists, vaccines against COVID-19 received regulatory approval for emergency human use in many jurisdictions in less than a year after the identification of the viral sequence. Several of these vaccines have been in use for some time; however, the pandemic is still ongoing and likely to persist for the foreseeable future. This is due to many reasons including reduced compliance with public health restrictions, limited vaccine manufacturing/distribution capacity, high rates of vaccine hesitancy, and the emergence of new variants with the capacity to spread more easily and to evade current vaccines. Here we discuss the discovery and availability of COVID-19 vaccines and evolving issues around mass vaccination programs.

Keywords: COVID-19; COVID-19 vaccines; SARS-CoV-2; vaccination; vaccine hesitancy.

Publication types

  • Open access
  • Published: 16 February 2024

Heterogeneity in COVID-19 vaccine uptake within low-income minority communities: evidence from the watts neighborhood health study

  • Elizabeth Wong   ORCID: orcid.org/0000-0001-7676-5462 1 ,
  • Ying Liu   ORCID: orcid.org/0000-0002-1101-0269 1 ,
  • Victoria Shier   ORCID: orcid.org/0000-0002-4171-5972 2 &
  • Ashlesha Datar   ORCID: orcid.org/0000-0001-8526-8804 1  

BMC Public Health volume  24 , Article number:  503 ( 2024 ) Cite this article

Metrics details

The literature on disparities in COVID-19 vaccine uptake focuses primarily on the differences between White versus non-White individuals or differences by socioeconomic status. Much less is known about disparities in vaccine uptake within low-income, minority communities and its correlates.

This study investigates disparities in COVID-19 vaccination uptake within racial and ethnic minoritized communities with similar socioeconomic backgrounds and built environments, specifically focusing on Black-Hispanic disparities and disparities within the Hispanic community by country of origin. Data are analyzed from the fourth wave (June 2021- May 2022) of the Watts Neighborhood Health Study, a cohort study of public housing residents in south Los Angeles, CA. Linear probability models estimated the association between vaccine uptake and participants’ race/ethnicity, sequentially adding controls for sociodemographic characteristics, health care access and insurance, prior infection, and attitudes towards COVID-19 vaccines. Differences in reasons for vaccination status by race/ethnicity were also tested.

Mexican Hispanic and non-Mexican Hispanic participants were 31% points (95% CI: 0.21, 0.41, p  < 0.001) and 44% points (95% CI: 0.32, 0.56, p  < 0.001) more likely to be vaccinated than non-Hispanic Black participants, respectively. The disparity between Black and Hispanic participants was reduced by about 40% after controlling for attitudes towards COVID-19 vaccines. Among Hispanic participants, non-Mexican participants were 13% points (95% CI: 0.03, 0.24, p  = 0.01) more likely to be vaccinated than Mexican participants, however, these differences were no longer significant after controlling for individual and household characteristics (β = 0.04, 95% CI: -0.07, 0.15, p  = 0.44).

There are sizeable racial and ethnic COVID-19 vaccination disparities even within low-income and minoritized communities. Accounting for this heterogeneity and its correlates can be critically important for public health efforts to ensure vaccine equity.

Peer Review reports

Introduction

In the United States (U.S.), the COVID-19 pandemic disproportionately affected racial and ethnic minoritized communities [ 1 , 2 ]. Due in part to socioeconomic factors (e.g., poverty, housing, employment, access to health care), Black and Hispanic individuals had a higher risk of infection, hospitalization, and death relative to White individuals [ 3 , 4 ]. In April 2021, COVID-19 vaccines became available to all adults in the U.S [ 5 ], and the federal government and many state governments made commitments to prioritizing vaccine equity [ 6 ]. However, nationwide vaccination efforts have been constrained by inequitable distribution of vaccines and racial, ethnic, and socioeconomic disparities in vaccine uptake [ 7 , 8 , 9 ].

The literature on COVID-19 vaccine disparities focuses primarily on the differences between White versus Black and/or Hispanic individuals. Studies have consistently found that Black individuals are significantly less likely than White individuals to be vaccinated, despite being at heightened risk for COVID-19 [ 10 , 11 , 12 ]. In the following months after vaccines became widely available to the public, an estimated 77.8% of White individuals had received at least one dose of a vaccine compared to 70.8% of Black individuals [ 13 ]. In contrast, findings regarding Hispanic-White vaccination disparities are mixed. While one study reported that Hispanic individuals, like Black individuals, are less likely to be vaccinated than Whites [ 12 ], another survey reported no significant differences between Hispanic and White respondents [ 11 ]. Further, a third study estimated that Hispanic individuals were 36% more likely to be vaccinated than White individuals [ 10 ]. The mixed results among Hispanic populations may be, in part, due to the diversity within this group. Napoles et al. (2021) confirm that, among Hispanic individuals, concerns about vaccine safety, effectiveness, and side effects vary by national origin. For example, Hispanic individuals from Mexico or South America more frequently reported favorable vaccine intentions compared to those with Puerto Rican, Cuban/Dominican, Central American, or other Hispanic ancestry [ 14 ].

To further understand and explain differences in vaccination status across racial and ethnic groups, a growing literature is exploring the underlying factors that predict vaccine uptake. Recent studies find that Black and Hispanic adults have higher rates of vaccine hesitancy compared to other racial and ethnic groups [ 15 , 16 ], and vaccine concerns, particularly related to safety and potential side effects, may partly explain these disparities [ 17 ]. Socioeconomic characteristics, such as education and income, are also significant predictors of vaccination status [ 10 , 18 ]; some studies indicate that Black-White and Hispanic-White disparities in vaccination status can be partly explained by socioeconomic disadvantages among Black and Hispanic communities [ 12 , 19 ].

But very little attention has been paid to heterogeneity in vaccine uptake within marginalized populations. In particular, few studies explore the intersection of race, ethnicity, and socioeconomic status to examine differences in vaccine uptake within and between racial and ethnic communities with similar socioeconomic disadvantages. Since vaccination uptake has plateaued for all racial-ethnic groups since around May 2022 [ 20 ], there is a critical need for identifying strategies to make further progress in vaccine uptake. Understanding the heterogeneity within minoritized communities and the factors that contribute to it can offer important insights for designing and targeting interventions for increasing vaccine uptake.

The present study contributes to the literature by examining the heterogeneity in vaccine attitudes and uptake within low-income communities, specifically focusing on Black-Hispanic disparities and disparities within the Hispanic community by country of origin. Using data collected from residents in urban public housing developments, the study seeks to address three aims: (1) determine whether racial and ethnic disparities in vaccine uptake exist within this community, (2) identify factors that explain heterogeneity across racial and ethnic groups, despite their similar socioeconomic backgrounds and exposure to similar geography-based environments, and (3) explore facilitators and barriers to vaccine uptake by race and ethnicity. The findings from this analysis can aid public health practitioners in developing more tailored strategies to improve vaccine uptake in low-income and marginalized communities.

Data and sample

Data are analyzed from the Watts Neighborhood Health Study (WNHS) [ 21 ], a cohort study designed to evaluate the impact of a public housing redevelopment in Watts, Los Angeles, California. Between May 2018 and December 2019, WNHS recruited 609 adult and 466 child residents from three public housing sites—Jordan Downs, Nickerson Gardens, and Imperial Courts—and followed them annually over three subsequent waves.

The current study uses survey data from the fourth wave, collected between June 2021 and May 2022, in which adult participants aged 18 and older were asked about their COVID-19 vaccination status, barriers and facilitators to getting a COVID-19 vaccine, attitudes towards COVID-19 vaccines, and pandemic-related hardships. A total of 726 adults participated in this wave, of which 664 adults (76.5%) were originally recruited at baseline, and 62 were child participants at baseline who transitioned to adulthood between baseline and the fourth wave. Of these, 73 adults moved out of the three public housing sites before the fourth wave and were therefore excluded from the analysis. Another 9 participants did not provide information on their vaccination status, the primary outcome of the current study, and one other participant reported race/ethnicity as neither Hispanic nor Black; all 10 of these participants were also excluded from the analysis. Additionally, a total of 27 participants had missing data for some of the covariates described below, and were handled via listwise deletion, resulting in a primary analytic sample of 616 (84.8%) participants.

In the third wave, fielded between June 2020 and April 2021, we asked participants about their access to health care. In the fourth wave analytic sample described above ( n  = 616), a total of 66 (10.7%) did not participate in wave three, reducing the sample to 550 participants. Below, we present the results using the larger analytic sample, however, repeating the same analyses using the smaller, restricted sample with data from both the third and fourth waves shows very similar results (Table S1 ).

The study was approved by Institutional Review Board at the University of Southern California.

Vaccination status

The primary outcome of interest was collected by asking participants: “Have you gotten vaccinated for the coronavirus?” (yes/no).

Race, ethnicity, and hispanic ancestry

The key predictor of interest was created based on two questions. First, throughout the four waves of data collection we asked participants to identify their race/ethnicity (Hispanic; Black or African American; White; American Indian or Alaska Native; Asian; or Native Hawaiian or other Pacific Islander), allowing participants to select multiple racial or ethnic groups. Second, during the fourth wave, we asked self-identified Hispanic participants about their Hispanic or Latino ancestry or origin using the following categories: Mexican, Mexican American, Chicano; Salvadoran; Guatemalan; Costa Rican; Honduran; Nicaraguan; Panamanian; Puerto Rican; Cuban; Spanish-American (from Spain); Other Hispanic, Latino or Spanish Origin (e.g., Salvadoran, Dominican, Columbian, Guatemalan, Spaniard, Ecuadorian). Because 75.2% of all Hispanic adult participants reported having Mexican ancestry, alone or combined with other origins, we compiled the responses from the two questions and created three race/ethnicity groups: (1) non-Hispanic Black, (2) Hispanic with Mexican ancestry, and (3) Hispanic with non-Mexican ancestry.

Attitudes about the COVID-19 vaccines

Six questions were administered to assess attitudes about COVID-19 vaccines. The first four questions asked participants how much they agreed or disagreed with statements that COVID-19 vaccines: (1) Have known harmful side effects; (2) Provide important benefits to society; (3) May lead to illness and death; (4) Are useful and effective. The response options for these first four questions included strongly disagree, disagree, neither agree nor disagree, agree, strongly agree. The remaining two questions asked how much the participants trusted: (5) The process in general (not just for COVID-19) to develop safe vaccines for the public; and (6) The governmental approval process to ensure the COVID-19 vaccine is safe for the public. Response options for these two questions included fully trust, mostly trust, somewhat trust, and do not trust. For each of the six statements, responses were recoded into a binary variable measuring pro-vaccine attitudes (1) versus neutral or anti-vaccine attitudes (0). For example, if an individual “disagreed” or “strongly disagreed” with the statement that the COVID-19 vaccines “have known harmful side effects,” they were coded as having pro-vaccine attitudes. Similarly, if an individual “agreed” or “strongly agreed” with the statement that COVID-19 vaccines “provide important benefits to society,” they were considered as having pro-vaccine attitudes.

Due to collinearity between some questions measuring COVID-19 attitudes, our primary regression analyses include three of these six variables that measure three distinct domains: perceived benefit (COVID-19 vaccine provides important benefits to society); perceived harm (COVID-19 vaccine may lead to illness and death); and perceived trust (trust the process in general (not just for COVID-19) to develop safe vaccines for the public). Sensitivity analyses show similar results when these three variables are replaced with the other three variables in the regression analysis (Table S2 ).

Prior COVID-19 infection

Information on participants’ COVID-19 infection status was collected by asking: “Do you think you’ve been infected with the coronavirus?” (yes/no).

COVID-19 related hardships

Participants were also asked to rate “how much of a problem were each of the following things during the past month,” on a scale of 1 to 10, where 1 means not a problem at all and 10 means a big problem: maintaining your income; staying connected with family; staying connected with friends; grocery shopping and access to food; having enough food for you and your family; going out to eat or for entertainment; and being able to exercise and physically active . Exploratory factor analysis showed a strong single factor structure among these items, with a single strong eigenvalue of 3.20 and a Cronbach’s alpha of 0.85. We used an average score in this analysis as it was almost perfectly correlated with the factor score ( r  = 0.99).

Health conditions and functional limitations

Because participants’ experiences during the pandemic and attitudes about COVID-19 vaccines may depend on their health status, we included three indicators in our analysis to measure health conditions and functional limitations: (1) whether the participant was ever diagnosed with any cardiometabolic conditions (heart disease, diabetes type 2, high blood sugar, hypertension, high cholesterol, or obesity; (2) whether he/she had “serious difficulty walking, climbing stairs, bathing, dressing or doing errands alone” (never, some of the time, a moderate amount of time, and most of the time, with the latter three options grouped to create an “any limitation” indicator); and (3) whether he/she had obesity. The obesity status was defined as having body mass index greater than or equal to 30.0. Trained staff collected weight and height measurements using a Tanita UM-081 digital scale and Charder HM200P Portstad Portable Stadiometer, respectively. A small portion of the participants (< 5%) did not have measurement data in the fourth wave, and therefore their weight and height information from earlier waves were used in the analysis.

Access to health insurance and health care

Participants’ attitudes about the COVID-19 vaccines might also reflect, to some degree, their general experience with the medical system. As such we included in the analysis participants’ self-reports on their access to health care during the earlier stage of the pandemic. Specifically, we asked: (1) “Do you currently have any health insurance coverage or some way to pay for your health care?” (yes/no); and (2) “Is there a place that you usually go to when you are sick or need advice about your health?” (yes/no). Participants were also asked where they received such care, including major hospitals and health centers nearby, as well as private practices. These responses were used to derive an indicator for whether a participant had access to medical professionals when needed. These questions were only asked in the prior year’s survey.

Time of the primary survey

Data was collected from participants over a year long period, during which the COVID-19 infection rate and the vaccination policy in Los Angeles County were rapidly changing. To address this we split the data collection window into two periods: (1) June to November 2021, soon after the COVID-19 vaccines became available to all adults in Los Angeles County in April 2021 and when the infection rate was relatively low; and (2) December 2021 to June 2022, during and after the Omicron surge when the infection rate peaked and went down [ 22 ]. We chose this breakdown because people’s attitudes about COVID-19 vaccines might have varied depending on the disease environment. Throughout the entire data collection period, participation was fairly balanced across race/ethnicity groups (Figure S1 ).

Demographic and household characteristics

Demographic information of the participants was also collected, including age (18–34, 35–54, 55 and older), gender (male/female), education (less than high school, high school, more than high school), whether married or living as married (yes/no), and in which country the participant was born (U.S./outside U.S.). Additional household information included income (less than $10,000, $10,000-$19,999, $20,000 and more), whether any household member worked for pay (yes/no), and the number of children in the household (none, one or two, three or more).

Reasons for vaccination status

Participants who were vaccinated were asked, “What is the main reason you chose to get vaccinated?”. Responses were grouped into four categories: (1) work or school mandate; (2) to protect oneself; (3) to protect family or others; and (4) other/unknown. Participants who were not vaccinated were asked, “What is your biggest barrier to getting the coronavirus vaccine?”. Responses were grouped into six categories: (1) distrust in COVID-19 or the vaccine; (2) concerns about vaccine safety; (3) underlying health condition(s); (4) waiting for additional information or unsure; (5) no barriers; and (6) other/unknown.

To estimate the association between the racial and ethnic groups and vaccination status, we used a “build” regression approach that adds blocks of covariates, one at a time, to predict vaccination status. We estimate linear probability models for easy interpretability of coefficients; logistic models yielded similar results (Table S3 ). Starting with a model with race/ethnicity groups and survey time period covariates, we added: (1) demographic and household characteristics, (2) prior infection with COVID-19, (3) health conditions and functional limitations, (4) COVID-19 related hardships in the past month, (5) attitudes about COVID-19 vaccines, and (6) access to health insurance and health care. Although the majority (56%) of participants came from single-respondent households, standard errors were clustered at the household level to account for household-level effects in cases where multiple respondents resided in the same household. Chi-squared tests were used to compare reasons for vaccination status between non-Hispanic Black and both Hispanic groups combined (due to sample size concerns). All analyses were conducted using Stata 16.1.

Table  1 presents the descriptive statistics for the analysis sample, overall and by race/ethnicity. Overall, about 22% of the sample was 55 years or older and 75% was female. Nearly one-third of the sample (27.9%) had less than a high school degree, 38.2% had a household income of less than $10,000 per year, and 40% were born outside the U.S. In addition, most of the sample had health insurance (86.4%) and access to a medical professional (88.8%).

With respect to racial/ethnic composition, 28.2% were non-Hispanic Black, 55.7% were Hispanic with Mexican ancestry, and 16.1% were Hispanic with non-Mexican ancestry. There were several significant differences in demographic and household characteristics by race/ethnicity. For example, education and household income varied significantly by race/ethnicity groups ( p  < 0.001 for both). Fewer non-Hispanic Black participants (10.9%) had less than high school education than Hispanic participants (32.1% of Mexican and 43.4% of non-Mexican Hispanic participants). More non-Hispanic Black participants had a household income of less than $10,000 than Hispanic participants (53.5% of non-Hispanic Black, 31.5% of Mexican Hispanic, 34.3% of non-Mexican Hispanic participants). Non-Hispanic Black participants were also less likely to have a household member who works for pay (52.9% vs. 87.2% and 72.7% for Mexican Hispanic and non-Mexican Hispanic participants, respectively; p  < 0.001) or be foreign born than other participants (0.6% vs. 51.0% and 73.7% for Mexican Hispanic and non-Mexican Hispanic participants, respectively; p  < 0.001).

Vaccination status and vaccine attitudes were significantly different between non-Hispanic Black participants and the Hispanic participants; 36.8% of non-Hispanic Black participants were vaccinated, compared to 67.4% of Mexican Hispanic and 80.8% for non-Mexican Hispanic participants ( p  < 0.001). Hispanic participants were also more likely to have pro-vaccine attitudes. About half of Mexican (51.6%) and non-Mexican (44.4%) Hispanic participants mostly trusted or somewhat trusted the process to develop a safe vaccine, compared to less than one-fourth of non-Hispanic Black participants (22.4%) ( p  < 0.001). There were similar patterns for attitudes about vaccines providing an important benefit to society and about vaccines not leading to illness or death.

Table  2 presents estimates from linear probability models for vaccination status, adding one block of covariates at a time. As shown in Model 0, before controlling for any covariates other than timing of the survey, vaccination status varied significantly by race/ethnicity. Mexican Hispanic and non-Mexican Hispanic participants were 31% points ( p  < 0.001) and 44% points ( p  < 0.001) more likely to be vaccinated than non-Hispanic Black participants. The difference in vaccination among Hispanic participants (shown at the bottom of the table) was also relatively large; non-Mexican Hispanic participants were 13% points ( p  = 0.011) more likely to be vaccinated than Mexican participants. After adding demographic and household characteristics (Model 1), the differences in vaccination status between non-Hispanic Black participants and Hispanic participants persisted. Hispanic participants (both Mexican and non-Mexican Hispanic) were at least 30% points more likely to be vaccinated than non-Hispanic Black participants. However, the difference in vaccination status between Hispanic participants based on ancestry was reduced; non-Mexican Hispanic participants were only 4% points more likely to be vaccinated than Mexican Hispanic participants ( p  = 0.417). Beyond race/ethnicity, the only demographic or household characteristic that was significantly associated with vaccination status was age; participants 55 years or older were 34% points more likely to be vaccinated than participants 18–34 years old ( p  < 0.001).

Adding covariates for whether the participant had a prior infection of COVID-19 (model 2), potential health conditions and functional limitations (model 3), and COVID-19 related hardships (model 4) did not explain the gap in vaccination between non-Hispanic Black and Hispanic participants. The difference in vaccination between non-Mexican Hispanic and Mexican Hispanic participants remained small and non-significant (4% points).

In Model 5, attitudes about the COVID-19 vaccine (trust to develop a safe vaccine, vaccine provides important benefit, and vaccine does not lead to illness or death) were added to the model. After controlling for these attitudes, disparities in vaccination between non-Hispanic Black and Hispanic participants were reduced by about 40%; Mexican and non-Mexican Hispanic participants were 19 and 22% points more likely to be vaccinated compared to non-Hispanic Black participants, respectively. Vaccine attitudes were significantly associated with vaccination. Fully trusting or mostly trusting the process to develop a safe vaccine was associated with 19% points higher likelihood of being vaccinated ( p  < 0.001). Strongly or somewhat agreeing with vaccines providing an important benefit to society was associated with 29% points higher likelihood of being vaccinated ( p  < 0.001), and strongly or somewhat disagreeing with vaccine leading to illness or death was associated with 17% points higher likelihood of being vaccinated ( p  < 0.001). Finally, adding health insurance and health care access variables (model 6), did not further explain the gap in vaccination status between non-Hispanic Black and Hispanic (Mexican or non-Mexican) participants. Predicted vaccination rates for each racial and ethnic group from each model are reported in Table S3 .

Table  3 presents the reasons for vaccination status for the full sample and by race/ethnicity. Overall, protecting oneself (48.7%) and protecting family or others (30.0%) were the two most cited reasons for vaccination among adults who were vaccinated. Among those who were not vaccinated, 34.6% cited distrust in COVID-19 or the vaccine as the biggest reason for their decision. The second most cited reason was concerns about vaccine safety (26.3%). When comparing racial/ethnic groups, there were some notable differences although they were not statistically significant. Compared to non-Hispanic Black participants, a notably higher percentage of Hispanic participants reported being vaccinated to protect their family or others (17.2% and 32.6%, respectively). A slightly higher percentage of non-Hispanic Black participants reported distrust (36.4%) and concerns about vaccine safety (29.1%) compared to Hispanic participants (33.1% and 23.9%, respectively).

Since the start of the pandemic, research has extensively documented racial, ethnic, and socioeconomic disparities in COVID-19 vaccine attitudes and vaccination status [ 15 , 23 , 24 ]. However, few of these studies have focused on the intersection of race, ethnicity, and socioeconomic status to understand vaccine disparities within low-income minoritized communities. The current study seeks to fill this research gap by examining the heterogeneity in vaccine attitudes and uptake within low-income and socially disadvantaged communities, specifically focusing on Black-Hispanic disparities and disparities within the Hispanic community by country of origin.

Our analyses reveal substantial disparities in vaccination status between low-income Black, Mexican Hispanic, and non-Mexican Hispanic groups. We find that low-income Hispanic individuals, regardless of their country of origin, are more likely than low-income Black individuals to receive the COVID-19 vaccine. Specifically, Hispanic individuals with Mexican ancestry are 31% points more likely than Black individuals to be vaccinated. The difference is even greater for non-Mexican Hispanic individuals, who are 44% points more likely thank Black individuals to be vaccinated.

The vaccination gap between low-income Black and Hispanic individuals residing in public housing developments is substantially larger than Black-Hispanic vaccination gaps reported in other studies which use more heterogeneous samples [ 12 , 13 ]. For example, a study of registered voters in California reported that 65% of Black respondents and 67% of Hispanic respondents reported receiving at least one dose of a COVID-19 vaccine [ 12 ]. Using nationally representative data from the Household Pulse Survey, another study also reported minimal differences between the estimated vaccination rates of Hispanic (74%) and Black populations (71%) [ 13 ]. It is possible that vaccination disparities between Black and Hispanic communities are concentrated within low-income groups. Therefore, evidence of these differences may be muted in studies that survey more diverse Black and Hispanic samples from a range of economic backgrounds.

Perhaps due to previous research that has demonstrated only slight differences between Black and Hispanic vaccination rates, little attention has been given to understanding vaccination disparities between these two groups. Most research investigating racial and ethnic vaccination disparities compare White individuals with minority groups. These studies commonly suggest that socioeconomic disadvantages (e.g., education, income, location) create structural and geographic barriers to COVID-19 vaccines for minority populations [ 12 , 19 , 25 ]. However, there are two indications to suggest that these barriers do not explain the sizeable Black-Hispanic COVID-19 vaccine disparity we find among low-income communities. First, our sample was recruited from three similar public housing developments in one south Los Angeles neighborhood, and there is little evidence of variation in vaccine accessibility within that community. Around May 2021, after vaccines became widely available to the public, community organizations, churches, and health care providers began partnering to bring mobile clinics and pop-up vaccination sites to the Watts neighborhood. Second, contrary to the literature, our results indicate that individual barriers, such as educational attainment, income, and health insurance coverage, do not significantly predict vaccination status. In fact, we find that Hispanic individuals, despite having lower levels of education, are actually more likely to be vaccinated than Black individuals. Moreover, access to health care (89%) and health insurance (86%) is also generally high in our sample, with relatively less variability across racial-ethnic minority groups, which might also explain why it did not predict vaccination status. Furthermore, recent evidence based on more representative samples from the 2022 US household pulse survey also suggests that insurance status was not predictive of COVID-19 vaccination status [ 10 ], perhaps due to its free availability and efforts to rapidly increase access both within and outside of traditional health care systems (e.g., via mass vaccination sites).

Rather, the results from these analyses demonstrate that attitudes about COVID-19 vaccines significantly predict vaccination status and play a large role in explaining the Black-Hispanic vaccine disparity. After accounting for individual attitudes about the COVID-19 vaccine, the Black-Hispanic (Mexican ancestry) disparity was reduced by nearly 40%, and the Black-Hispanic (non-Mexican ancestry) was reduced by 50%. These findings may be driven, in part, by more positive attitudes about the COVID-19 vaccines among Hispanic communities compared to Black communities. Indeed, in our sample, 48% of Hispanic individuals of Mexican ancestry and 56% of Hispanic individuals of non-Mexican ancestry trusted the government to develop a safe COVID-19 vaccine, compared to only 22% of Black individuals. This trend is consistent with other studies from California and the U.S. which show that Black individuals more frequently report negative vaccine attitudes and perceptions relative to Hispanic individuals [ 26 , 27 , 28 ].

While our analyses suggest that vaccine attitudes explain a notable portion of the Black-Hispanic vaccination disparity, our models were unable to explain the full difference. Even after accounting for age, sex, education, employment status, household composition, health status, vaccine attitudes, health insurance coverage, and health care access, we find that Hispanic individuals are still roughly 20% points more likely to be vaccinated than Black individuals. This indicates that there are other factors leading to vaccine disparities between Hispanic and Black individuals.

One potential explanation could be industry and occupational differences between Black and Hispanic workers in our sample, and varying exposure to COVID-19 mandates. Using data from the 2019 American Community Survey, a recent paper reported that Hispanic workers are employed in the U.S. health care workforce at slightly higher rates than Black workers (18.2% and 12.1%, respectively) [ 29 ]. In California, health care workers were required to be fully vaccinated starting August 2021. If Hispanic participants were employed more frequently in the health care or any other sector that mandated COVID-19 vaccination, they may have been more likely to receive the vaccine. However, our data shows that Black and Hispanic individuals in our sample had similar experiences with workplace vaccine mandates, although Black participants were less likely to have a working household member than Hispanic participants. Among respondents who were vaccinated, we find no significant difference between the number of non-Hispanic Black individuals (16%) and Hispanic individuals (11%) who reported workplace mandates as the primary reason for being vaccinated. This suggests that industry and occupational differences likely do not explain vaccine disparities within our sample.

Other studies have also considered the role that discrimination plays in creating and perpetuating medical mistrust, and the effect that this process has in explaining vaccine hesitancy and uptake [ 30 ], particularly among racial and ethnic minoritized communities [ 12 , 15 , 31 ]. Because our study did not collect this information from participants, we were unable to examine how these factors relate to disparities in vaccine attitudes or vaccine uptake between low-income Black and Hispanic individuals. Nonetheless, future studies may consider investigating whether and how experiences with discrimination and medical mistrust explain disparities in vaccination attitudes and behaviors between these two marginalized groups. It is also important for future research to consider how institutional efforts to improve trust and communication between communities and health care professionals could support vaccine equity [ 32 ].

A unique contribution of these analyses was the ability to look at vaccine disparities within the Hispanic community. Based on a previous study that documented differences in vaccine intention and concerns between Hispanic individuals depending on national origin [ 14 ], we expected to see differences in vaccination status between Hispanic individuals with Mexican ancestry and Hispanic individuals with non-Mexican ancestry. In our base model, we do find evidence to suggest significant differences, where Hispanic individuals with non-Mexican ancestry are 13% points more likely to be vaccinated than Hispanic individuals with Mexican ancestry. This contrasts with findings from Napoles et al. (2021) who found that individuals of Mexican origin more frequently reported positive vaccine intention compared to individuals from other Hispanic origins including those of Puerto Rican, Cuban/Dominican, and Central American descent [ 14 ]. Interestingly, after accounting for individual and household characteristics, any differences between non-Mexican and Mexican Hispanic individuals are attenuated and no longer significant.

These results may be driven by differences within the non-Mexican Hispanic sample—because over three quarters of Hispanic participants were of Mexican ancestry, we grouped Hispanics with Salvadoran, Guatemalan, Costa Rican, Honduran, Nicaraguan, Panamanian, Puerto Rican, Cuban, or other ancestry into a single comparison group. The small sample sizes of these other groups limit our ability to conduct a more detailed analyses. However, as we know from the literature, these are all heterogenous Hispanic communities and have different beliefs and experiences related to the pandemic and the COVID-19 vaccines. Future studies with access to a more diverse sample of Hispanic individuals should consider exploring more deeply the differences in vaccination rates based on national origin.

Our study has some limitations that should be considered when interpreting these results. First, our survey broadly asked participants whether they had been vaccinated for the coronavirus but did not specifically ask whether they had received a single dose, the full primary series, or any booster. Participants may have interpreted this question differently. Second, vaccination status was self-reported during a phone-based survey and may be subject to social desirability bias. Third, our sample of low-income public housing residents was recruited from one urban community in south Los Angeles. Given that states and counties took unique approaches to managing the virus and administering vaccines, these results may not be generalizable to low-income public housing residents in other regions, other states, or even other cities within California.

In conclusion, this study advances the current literature on racial and ethnic differences in COVID-19 vaccine attitudes and uptake. Previous studies have largely framed vaccine inequity around differences in vaccine uptake between White communities and Black and/or Hispanic communities, thus the proposed solution is often a blanket call for targeted public health messaging to increase vaccination rates among minority populations, generally. However, this study reveals that there are prominent racial and ethnic disparities in vaccine attitudes and vaccine uptake within minoritized groups. The results highlight the importance of acknowledging heterogeneity within marginalized communities, supporting the idea that there is no “one-size-fits-all” solution to achieving vaccine equity [ 33 ]—tailored approaches for Mexican American communities may not be effective in other Hispanic communities. Identifying and understanding these differences are critical to developing more nuanced public health messaging to improve vaccine equity, not just for COVID but also for vaccines more generally.

Data availability

The de-identified individual-level dataset used during this current study can be made available from the corresponding author upon reasonable request.

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Acknowledgements

The authors acknowledge the generous support of the Housing Authority of the City of Los Angeles (HACLA) for conducting this study. The authors thank the Community Coaches and residents at the study sites for their participation and support for this study.

This research was supported by grants from the National Cancer Institute (R01CA228058) and the Eunice Kennedy Shriver National Center for Child Health and Human Development (R01HD096293). All opinions are those of the authors and not of the funding agency.

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Ashlesha Datar, Victoria Shier, Ying Liu contributed to the study conception and design. Data analysis was performed by Ying Liu. All authors contributed to the data interpretation, the first draft of the manuscript and revisions to the manuscript. All authors read and approved the final manuscript.

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Wong, E., Liu, Y., Shier, V. et al. Heterogeneity in COVID-19 vaccine uptake within low-income minority communities: evidence from the watts neighborhood health study. BMC Public Health 24 , 503 (2024). https://doi.org/10.1186/s12889-024-17968-2

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Literature review on COVID-19 vaccine efficacy in the immunocompromised population, and possible implications to future vaccination in kidney transplant patients

Joo kyung park.

1 Department of Renal Medicine, Hull University Teaching Hospitals NHS Trust, Kingston upon Hull, United Kingdom

Sunil Bhandari

2 Hull York Medical School, Kingston upon Hull, United Kingdom

Since the emergence of the virulent coronavirus in 2019, efforts to tackle the coronavirus-disease-2019 (COVID-19) pandemic have been made globally. The development of the coronavirus disease (COVID) vaccine was a significant breakthrough in ways to tackle the virus. Various research studies have been conducted to identify how the virus works and ways to manage COVID, including the efficacy of the vaccines. However, there is limited data on how these measures work for the immunocompromised, despite the grave impact of these virulent strains in this population. Specifically, this review aims to focus on kidney transplant recipients (KTRs). Studies have suggested that there is significantly lower vaccine response in some immunocompromised groups despite additional booster doses, and hence warrants an augmented or alternative protection against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) for these patients. This suggests a need for alternative or more tailored approach in providing adequate protection against the COVID-19 in these cohorts. Some suggested ways include withholding immunosuppressants before and/or after vaccination, increasing the vaccine doses or reducing intervals and providing a mixture of monoclonal antibody (mAb) or antiviral therapy. However, the appropriate degree of alteration and augmentation, as well as its safety and effectiveness remains to be determined. Furthermore, continuous emergence of more virulent strains, such as the Omicron and its sub-lineages or the Deltacron, emphasises the need for ongoing research to assess the effectiveness of the current treatment against these new variants. Overall, active interest and appropriate updates to COVID-19 guidelines is necessary.

Introduction

In 2019, a highly transmissible and pathogenic version of coronavirus, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), caused a global pandemic of Coronarvirus-Disease-2019 (COVID-19) that caused about 540 million confirmed cases and 6.3 million deaths ( 1 ). From immunocompromised to the general population ( 2 ) and from clinical to socio-economic implications ( 3 , 4 ), COVID-19 had a significant effect on everyone. The emergence of such a severe and acute pandemic prompted a collaborative effort worldwide to tackle the virus, which included public health protection measures (isolation, social-distancing, hand-washing, mask wearing, intermittent lockdowns) and ultimately vaccinations. Several different COVID-19 vaccines have been developed from pharmaceutical companies at breakneck speed ( 4 , 5 ), with many studies supporting the effectiveness of these vaccines in reducing mortality, disease severity and infection risk ( 5 – 10 ). However, there have been fewer studies comparatively that have examined vaccine efficacy in immunocompromised patients ( 2 ), despite the possible graver risks and consequences they face during this pandemic ( 11 ). Recent research demonstrates that the immunocompromised (such as those on immunosuppressive therapy or with a transplanted organ) may not achieve the same level of protection as the immunocompetent ( 2 , 12 – 16 ). This review explores the current evidence for vaccine efficacy in the immunocompromised, specifically kidney transplant population, and its implications in respect to current COVID-19 preventative guidelines in the United Kingdom (UK).

Vaccine response

A systemic meta-analysis reviewed 82 studies looking into seroconversion from the COVID-19 vaccine to compare its efficacy in the immunocompromised and the immunocompetent population ( 2 ). The majority of the included studies used messenger ribonucleic acid (mRNA) vaccines, although there were viral vector and inactivated whole virus vaccines included. The meta-analysis showed that organ transplant recipients were 16 times less likely to seroconvert after the first dose of a COVID-19 vaccine. Although a second dose improved seroconversion, it was of lower magnitude for organ transplant recipients, where only a third of the patients achieved seroconversion ( 2 ). The study suggested possible benefit of further vaccine doses ( 11 ), but recent data has shown persistently impaired spike protein response in a significant cohort of KTRs despite booster doses ( 12 , 13 ). This poses the question of the benefit of additional doses in such cohorts, and may warrant the need of a guideline that appropriately advises additional protection methods against COVID-19 for this high risk group.

Focusing on kidney patients, the RECOVAC Immune-response Study, a multi-centre research in the Netherlands, demonstrated a significantly lower seroconversion rate in KTRs ( 14 ). The study analysed SARS-CoV-2 Spike S1-specific immunoglobulin G (IgG) antibody response, virus neutralising antibodies and SARS-CoV-2-specific T-cell response after two doses of mRNA COVID-19 vaccine in 800 participants of four different cohorts: 162 participants with chronic kidney disease (CKD) stage 4/5, 159 patients on dialysis, 288 KTRs and 191 controls. The data was collected over 4-month period in 2021 from February to May, at four different outpatient clinics of university medical centres in Netherlands. Data showed a seroconversion rate of 21.2% in KTRs, whereas 99% in controls, 96.3% in CKD stage 4/5, and 87.4% in dialysis cohorts. After the second dose, seroconversion rates improved to 56.9% in KTRs, although it was still much lower than 100% in the control group ( 14 ). Additionally, RECOVAC and several other studies further suggested older age, lower estimated glomerular filtration rate (eGFR), lower lymphocyte count, using mycophenolate mofetil/mycophenolic acid, not using steroids, and shorter time after transplantation to be associated with increased risk of being a non-responder ( 14 – 16 ). One study stated that lower lymphocyte count below 1.3 G/L associated with chronic immunosuppressive treatment was highly predictive of poor immune response in CKD patients ( 16 ). A single centre study with 707 KTR participants in the UK further suggested maintenance with mycophenolic acid to have the most negative impact on vaccine response ( 12 ). This again highlights the need for further research into these cohorts and possible additional measures to achieve a level of protection against COVID-19, including additional or alternative vaccination strategies ( 14 – 16 ).

The above mentioned studies and others point towards reduced vaccine response in allograft recipients after two ( 2 , 15 , 16 ) and even three ( 15 , 17 ) doses of SARS-CoV-2 vaccine compared to the general population. However, some smaller sample studies showed possible benefit of further boosters ( 17 – 19 ). Both studies by Kamar et al. ( 19 ) and Alejo et al. ( 18 ) showed slightly improved humeral response after a fourth mRNA vaccine in patients with weak or no response after three doses. However, their sample sizes were 37 and 18 patients, respectively. Benotmane et al. ( 17 ) recruited 67 KTRs with low immune response after three mRNA vaccine doses and showed an improved serum neutralisation against the Delta variant, with an increase in proportion of patients having neutralising antibodies from 16 to 66% after the fourth vaccine. However, one third of the study sample remained unable to elicit serum neutralising antibodies. Despite the small sample size, this indicated that additional doses of COVID-19 vaccines may be beneficial in transplant patients even in previously weak or non-responders. To further support this, Osmanodja et al. ( 20 ) performed a retrospective study on 1,478 patients to look into dose adjustment regimens of mycophenolic acid on serological response against a fourth COVID vaccine. They concluded that up to five vaccine doses induced serological response effectively in KTRs, and that it could be further enhanced by pausing mycophenolic acid at the time of vaccination (except in those on belatacept therapy). This raises the question of potential benefit in higher or additional doses, prophylactic monoclonal anti-SARS-CoV-2 antibodies or even immunosuppressive modulation ( 17 , 20 ).

Since the development of COVID vaccines, various SARS-CoV-2 variants have emerged, raising concerns of vaccine effectiveness against the newer dominant strains ( 21 – 23 ). Many of the studies were designed to assess effects of some combination of Moderna, AstraZeneca, or Pfizer vaccines, and they have shown levels of protection against the alpha, epsilon, beta, gamma etc., up to delta variants ( 17 , 18 , 21 ). More recent research aims to assess vaccine durability against the Omicron sub-lineages ( 22 – 24 ). Kirsebom et al. ( 22 ) conducted a test-negative case-control study that assessed vaccine efficacy against the Omicron in the UK, which included all vaccines used in England -Pfizer and/or Moderna. From January to March 2022, they accumulated 1,127,517 eligible symptomatic individuals’ test samples, of which 265,820 were BA.1 positive and 1,246,069 BA.2 positive, whilst 615,628 were negative controls. The vaccine effectiveness after the first dose was 14.8% against BA.1 and 27.8% against BA.2. This increased to 70.6% against BA.1 and 74.0% against BA.2 after booster doses, waning to 37.4 and 43.7%, respectively after 15 or more weeks post-booster dose. They concluded that there was no evidence of reduced vaccine effectiveness against symptomatic BA.2 disease compared to that of BA.1, and that there was no difference in rate of vaccine effectiveness decline as well. Although these results are consistent with neutralisation assays reported by the UK Health Security Agency ( 25 ), it differs from a Danish household transmission study that reported increased COVID infection susceptibility against BA.2 despite vaccination ( 26 ). Lyngse et al. ( 26 ) identified 17, 319 secondary infections in 22, 678 primary cases in a 1–7 day follow-up, concluding that the secondary attack rate was higher in Omicron BA.2 variant than that of BA.1, 39% and 29%, respectively. However, Kirsebom et al. ( 22 ) suggested that such discrepancy in the UK and Denmark studies may be due to differences in vaccination and previous infection history in these countries or due to methodology and study design, and that further research would be beneficial.

A single centre study from Ohio, United States (US), evaluated neutralising antibody titres against previous SARS-CoV-2 strains with D614G mutation, BA.3 and Deltacron ( 24 ). They sampled 10 vaccinated healthcare workers, 18 intensive care unit (ICU) patients 3 days post-admission regardless of vaccination status during Delta wave of the pandemic, and 31 hospitalised during the Omicron wave. The data was compared with prior reports on BA.1, BA.2 and Delta variants ( 24 ). In the healthcare worker cohort, neutralising antibody titres were 3.3 times as low against BA.3 and 44.7 times as low against the Deltacron variant. This proved to be 2.9 times as low in BA.3 and 13.3 times as low in Deltacron variants after a booster dose. In ICU patients, the titres against Deltacron were significantly lower –137.8 times as low as the titres against D614G variant. Interestingly, only 44.4% of the ICU cohort had titre levels above the limit of detection. The titre levels against D614G and BA.3 were similar. In the hospitalised during Omicron wave without ICU admission group, Deltacron and BA.3 neutralisation titres were similar, although much lower than data obtained during the Delta wave. Fully vaccinated healthcare workers with a booster dose had greater immune cover than the other cohorts during the Omicron wave, regardless of the vaccination status –titres 59.9 times higher than the patient cohorts. Evans et al. ( 24 ) concluded that the evolution of SARS-CoV-2 and possible emergence of more virulent variants are significant concerns that require attention.

The UK Medicines and Healthcare products Regulatory Agency approved the first bivalent COVID booster in late 2022 ( 27 ). This is a vaccine by Moderna that targets two COVID variants, hence containing 25 micrograms each of the vaccines targeting the original 2020 strain and the Omicron. It claims that exploratory analysis of the bivalent vaccine showed positive immune response against BA.4 and BA.5 Omicron sub-variants. This is supported from recent data which saw better neutralising activity in BA.5-containing bivalent booster against all Omicron variants including the newer BQ.1.1 and XBB strains compared to the monovalent booster cohorts ( 28 ). However, they noted generally reduced monovalent and bivalent vaccine neutralisation efficacy against the newer WA1/2020, XBB and BQ.1.1 strains ( 28 ). On the other hand, Wang et al. ( 29 ) reported significantly reduced neutralising capability of the mAb and vaccines against the newer BQ.1, BQ.1.1, XBB and XBB.1 subvariants, raising concerns on our current counter measures against COVID. Again, given the ongoing viral evolution, continuous research and attention to the immunocompromised population is crucial to optimally protect KTRs.

Despite additional booster doses, several studies suggest persistently weak or non-responders to the vaccine in the immunocompromised ( 13 , 17 , 18 ). Therefore, it may be beneficial for guidelines to routinely check vaccine response in KTRs after three to four vaccine doses to identify such cohorts, and to subsequently offer mAb or alternative methods of protection empirically to minimise severe disease. Although possibly expensive to realise, the potential cost savings of avoiding hospital admission and possible graft loss would be even greater, not to mention the impact on quality of life. A vaccination approach suggested by Caillard and Thaunat ( 13 ) proposes to incorporate routine spike antibody level check in order to provide sufficient protection against COVID. They recognised that specific follow-up with personalised intensified vaccination approach for KTRs is required, given numerous reports of only 4–48% of KTRs having detectable anti-spike IgG after the second vaccine. This approach considers measuring the anti-spike IgG levels after two doses of mRNA vaccine if no COVID history, and after the first vaccine with a previous positive COVID history. If spike antibody levels were low, it further suggests either considering additional booster doses, reducing mycophenolate mofetil dose and/or replacing it with belatacept, or providing primary prophylaxis with mAb based on the anti-spike IgG or spike-specific T-cell interferon-gamma responses. However, more data on the outcome of these recommendations are needed as, for instance, some studies showed a weak antibody response to three COVID vaccine doses in KTRs on belatacept ( 30 ).

There is still a lack of cumulative data to sufficiently advise a definite guideline. Although the presence of a cohort of weak or non-responders of vaccine have been identified, whether the failure to develop the anti-spike IgG implies continued SARS-CoV-2 susceptibility remains unclear ( 11 , 31 ). Furthermore, the appropriate approach for enhanced COVID prevention is undetermined. Some suggest enhanced vaccination strategies, such as mixed dosing of vaccines with different mechanism of actions, alternative vaccination schedules, or even different dosing regimens ( 13 , 31 , 32 ). Others consider alternative strategies like mixture of mAb or altering immunosuppressive therapy ( 12 , 33 ). Regardless, further studies are warranted to understand and establish the most appropriate approach to improve COVID-19 vaccine response and public health measures to protect the immunocompromised patients.

Currently in the UK, mAb are recommended as general COVID-19 treatment given that the patient meets certain criteria ( 34 ). There have been studies supporting positive therapeutic use of anti-spike mAb in KTRs ( 35 – 37 ) with mild COVID-19 infections as well. Ongoing research is looking into use of these neutralising mAb as preventative measures of COVID-19 in immunocompromised patients. A nationwide study in France compared COVID-related hospitalisation, 30-day ICU admission, and 30-day mortality rate in KTRs who received early mAb infusion and those who did not ( 37 ). Out of 235 KTRs, 80 patients received early mAb. The early mAb group had less COVID-related hospitalisation, ICU admission and 30-day mortality (35% vs. 49.7% in control), and no mechanical ventilation was required. This supported possible benefits of early administration of mAb in KTRs with mild COVID-19 via passive immunity.

Another interesting concept is using a mixture of mAb as a preventative and/or therapeutic management. For instance, REGN-COV2 is an antibody cocktail containing two mAb under ongoing double-blind study for its effect on reducing SARS-CoV-2 viral load, and its potential therapeutic and preventative use against COVID-19 ( 38 ). Their hypothesis is that COVID-19 mortality and complications are related to the viral load, and thus reducing the viral burden should result in clinical improvement. This was based on some recent data showing high viral titres in hospitalised patients ( 39 ), and increased mortality risk in higher viral loads ( 40 ). The in vivo studies in non-human primates showed significant reduction in viral load and enhanced viral clearance with REGN-COV2 in prophylactic and therapeutic contexts, respectively. In clinical context, their data showed enhanced viral clearance especially in patients with negative serum antibody, in other words whose endogenous immune response has not yet been initiated, or in those with high viral load at baseline. With patients who were already serum antibody positive, the exogenous mAb mixture did not improve immune response greatly, nor did it hinder the ongoing antiviral activity. This suggests prophylactic benefit in immunocompromised patients who did not have sufficient vaccine response to enhance protection against the virus.

Unfortunately, many clinical trials on mRNA COVID vaccines approved under Emergency Use Authorization in the US and Europe excluded patients on immunosuppressive therapy ( 33 ). However, there were reasonable suspicions of possible effects of immunosuppressants on vaccine efficacy. For instance, an American research group used a mouse model to demonstrate that immunosuppressive medications in autoimmune conditions may impair COVID-19 vaccine response ( 41 ). They treated mice with five different immunosuppressants: cyclophosphamide, leflunomide, methotrexate, methylprednisolone or mycophenolate mofetil, and compared the immune cell population pre- and post-immunisation with SARS-CoV-2 spike protein. All tested immunosuppressive therapies significantly reduced the serum antibody titres in the experimented mice.

Applying this to humans, a US case study of a 75 year-old male with myasthenia gravis under high-dose prednisone and mycophenolate reported no detection of SARS-CoV-2 neutralising antibodies after 4 weeks of the second mRNA vaccine ( 33 ). The patient received second series of Pfizer mRNA vaccination 42 days (first dose) and 63 days (second dose) following the last set of vaccines. But for the second series, he also had reduced dose of mycophenolate 3 weeks prior to the first vaccine and held both prednisone and mycophenolate the day before and three subsequent days after the second vaccine. No change in clinical status was noted throughout this observational study. Interestingly, neutralising antibodies were detected 2 weeks post-vaccination, suggesting improved immune response to COVID-19 vaccine after a pause in immunosuppressive therapy.

Specific to KTRs, the CPAT-ISR and BECAME trials are examples of prospective studies that aim to assess the effects of reduced immunosuppressive therapy in improving vaccine response in KTRs ( 42 , 43 ). The CPAT-ISR is a US trial to assess COVID-antibody response to additional mRNA booster doses in kidney and liver transplant patients, either with or without immunosuppressant reduction ( 42 ). It will collect data from 15 different transplant centres across the US to observe if temporary dose reduction in immunosuppressants 5 days before and 2 weeks after booster doses will improve antibody response. Similarly, BECAME is a single-centre, investigator-initiated randomised controlled trial in Israel that will compare the SARS-Cov-2 seropositivity rate after third booster in patients with without reduced anti-metabolite ( 43 ). Although a smaller sample size compared to the CPAT-ISR, it will also look into T-cell response and perform an additional prospective observational study to include KTRs who received three vaccine doses, but were not eligible for the randomised controlled trial. Such trials will hopefully help identify how beneficial immunosuppressant modulation would be in improving vaccine response, and to establish a standard regime of approach on duration and dosing of reduction.

Given the nature of the rapidly evolving virus, studies and guidelines are being updated with possible need of holistic review and clarification. The UK Kidney Association provided a statement in December 2022 which recommended up to 6 doses of the vaccine in KTRs and patients with kidney disease on significant immunosuppressive therapy, and for offering COVID antibody testing for high-risk patients ( 44 ). They also acknowledged the need of clarification of mAb in CKD4/5 patients, in line with some recent studies suggesting clinical inefficacy of some mAb (amubarvimab, romlusevimab, sotrovimab, casirivimab-imdevimab, and amubarvimab-romlusevimab) and suggesting additional paxlovid ( 45 ). However, current regulations and recommendations remain to limit safe use of paxlovid or remdesivir in renal impairment patients ( 44 ). Evulsheld (Tixagevimab and casirivimab), currently under PROVENT phase III trial which includes CKD and immunocompromised patients, was given emergency use authorisation for the FDA ( 46 ), which may be a potential alternative and/or additional option for protection as suggested by the National Kidney Foundation ( 47 ).

Continued global efforts to appropriately update our COVID management approach are essential to ensure protection of our immunocompromised patients. With less restrictive public regulations and newer studies suggesting a significant cohort of insufficient vaccine responders, guidelines should be revised/updated to reflect this. Routinely measuring vaccine response via spike antibodies and serum neutralisation, and thus offering mAb, alternate vaccine regimen or immunosuppression reduction as appropriate may be considered and studied. Efforts to promote vaccination and reduce vaccine hesitancy, and continued public precautions and care when visiting hospitals should be encouraged. Above all, further research is crucial to identify and establish appropriate measures, alongside active engagement from the government, healthcare and the public in order to continue to protect both the immunosuppressed and immunocompetent population.

Author contributions

Both authors listed have made a substantial, direct, and intellectual contribution to the work, and approved it for publication.

Funding Statement

This study was funded by the National Health Service and National Healthcare System in the United Kingdom.

Abbreviations

ANCA, antineutrophil cytoplasmic antibodies; CKD, chronic kidney disease; COVID, coronavirus disease; COVID-19, coronavirus disease 2019; CPAT-ISR, COVID protection after transplant-immunosuppression reduction study; eGFR, estimated glomerular filtration rate; IgG, immunoglobulin; ICU, intensive care unit; KTRs, kidney transplant recipients; NHS, national health service; mRNA, messenger ribonucleic acid; mAb, monoclonal antibodies; PITCH, protective immunity from T cells to COVID-19 in health workers study; RECOVAC, renal patients COVID-19 vaccination study; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; UK, United Kingdom; US, United States.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

COVID-19 vaccines: Get the facts

Looking to get the facts about COVID-19 vaccines? Here's what you need to know about the different vaccines and the benefits of getting vaccinated.

As the coronavirus disease 2019 (COVID-19) continues to cause illness, you might have questions about COVID-19 vaccines. Find out about the different types of COVID-19 vaccines, how they work, the possible side effects, and the benefits for you and your family.

COVID-19 vaccine benefits

What are the benefits of getting a covid-19 vaccine.

Staying up to date with a COVID-19 vaccine can:

  • Help prevent serious illness and death due to COVID-19 for both children and adults.
  • Help prevent you from needing to go to the hospital due to COVID-19 .
  • Boost your body's protection, also called immunity, against catching the virus that causes COVID-19 .
  • Be a safer way to protect yourself compared to getting sick with the virus that causes COVID-19 .

How much protection a COVID-19 vaccine gives depends on different factors. Factors that can affect how much you're protected with a vaccine can include your age, if you've had COVID-19 before or if you have medical conditions such as cancer.

How well a COVID-19 vaccine protects you also depends on how the virus that causes COVID-19 changes and what variants the vaccine protects against. Your level of protection also depends on timing, such as when you got the shot.

Talk to your healthcare team about how you can stay up to date with COVID-19 vaccines.

Should I get the COVID-19 vaccine even if I've already had COVID-19?

Yes. After you've had COVID-19 , getting vaccinated can boost your body's protection against catching the virus that causes COVID-19 another time.

Getting COVID-19 or getting a COVID-19 vaccination gives you protection, also called immunity, from being infected again with the virus that causes COVID-19 . But over time, that protection seems to fade. Getting COVID-19 again may cause serious illness or medical complications, especially for people with risk factors for severe COVID-19 .

Researchers continue to study what happens when someone has COVID-19 a second time. Reinfections are generally milder than the first infection. But severe illness can still happen. Some people may see their risk of having to go to the hospital and having medical problems such as diabetes go up with each COVID-19 infection.

Research has found that people who have had COVID-19 and then have had all of the suggested COVID-19 vaccinations are less likely to be treated in the hospital due to COVID-19 than people who are not vaccinated or who haven't had all the suggested shots. This protection wears off in the months after getting the vaccine.

Also, because the virus that causes COVID-19 can change, also called mutate, a vaccination with the latest strain, or variant, that is spreading or expected to spread can help keep you from getting sick again.

Safety and side effects of COVID-19 vaccines

What covid-19 vaccines have been authorized or approved.

The COVID-19 vaccines available in the United States are:

  • 2023-2024 Pfizer-BioNTech COVID-19 vaccine, available for people age 6 months and older.
  • 2023-2024 Moderna COVID-19 vaccine, available for people age 6 months and older.
  • 2023-2024 Novavax COVID-19 vaccine, available for people age 12 years and older.

In general, people age 5 and older with typical immune systems can get any vaccine that is approved or authorized for their age. They usually don't need to get the same vaccine each time.

Some people should get all their vaccine doses from the same vaccine maker, including:

  • Children ages 6 months to 4 years.
  • People age 5 years and older with weakened immune systems.
  • People age 12 and older who have had one shot of the Novavax vaccine should get the second Novavax shot in the two-dose series.

Talk to your healthcare professional if you have any questions about the vaccines for you or your child. Your healthcare team can help you if:

  • The vaccine you or your child got earlier isn't available.
  • You don't know which vaccine you or your child received.
  • You or your child started a vaccine series but couldn't finish it due to side effects.

At the start of the COVID-19 pandemic, COVID-19 vaccines were needed right away. But the U.S. Food and Drug Administration's (FDA's) vaccine approval process can take years.

To provide vaccines sooner, the FDA gave emergency use authorization to COVID-19 vaccines based on less data than is typically required. But the data still has to show that the vaccines are safe and effective.

In August 2022, the FDA authorized an update to the Moderna and the Pfizer-BioNTech COVID-19 vaccines. Both included the original and omicron variants of the virus that causes COVID-19 .

In June 2023, the FDA directed vaccine makers to update COVID-19 vaccines. The vaccines were changed to target a strain of the virus that causes COVID-19 called XBB.1.5.

In September and October 2023, the FDA authorized the use of the updated 2023-2024 COVID-19 vaccines made by Novavax, Moderna and Pfizer-BioNTech.

Vaccines with FDA emergency use authorization or approval include:

2023-2024 Pfizer-BioNTech COVID-19 vaccine. This vaccine was first tested against the original strain of the COVID-19 virus. That strain began spreading at the end of 2019. In December 2020, the Pfizer-BioNTech COVID-19 vaccine two-dose series was found to be both safe and 91% to 95% effective in preventing COVID-19 infection in people age 18 and older. This data helped predict how well the vaccines would work for younger people. The effectiveness varied by age.

The Pfizer-BioNTech vaccine is approved under the name Comirnaty for people age 12 and older. It is authorized for people age 6 months to 11 years. The number of shots in this vaccination series varies based on a person's age and COVID-19 vaccination history.

2023-2024 Moderna COVID-19 vaccine. This vaccine also was first tested against the original strain of the virus that causes COVID-19 . In December 2020, the Moderna COVID-19 vaccine was found to be both safe and about 93% effective in preventing infection among study volunteers, all age 18 or older.

Based on the comparison between people who got COVID-19 in the placebo group, the Moderna COVID-19 vaccine was 98% effective at preventing serious COVID-19 illness. Vaccine effect was predicted for younger people based on that clinical trial data as well.

The vaccine is approved under the name Spikevax for people age 12 and older. The vaccine is authorized for use in people age 6 months to 11 years. The number of shots needed varies based on a person's age and COVID-19 vaccination history.

  • 2023-2024 Novavax COVID-19 vaccine, adjuvanted. This vaccine is available under an emergency use authorization for people age 12 and older. It requires two shots, given 3 to 8 weeks apart. Research done before the spread of the delta and omicron variants has shown that the vaccine is 90% effective at preventing mild, moderate and severe disease with COVID-19 . For people age 65 and older, the vaccine is 79% effective.

How do the COVID-19 vaccines work?

Both the Pfizer-BioNTech and the Moderna COVID-19 vaccines use genetically engineered messenger RNA (mRNA). Coronaviruses have a spikelike structure on their surface called an S protein. COVID-19 mRNA vaccines give your cells instructions for how to make a harmless piece of an S protein.

After vaccination, your muscle cells begin making the S protein pieces and displaying them on cell surfaces. The immune system recognizes the protein and begins building an immune response and making antibodies. After delivering instructions, the mRNA is immediately broken down. It never enters the nucleus of your cells, where your DNA is kept.

The Novavax COVID-19 , adjuvanted vaccine is a protein subunit vaccine. These vaccines include only the parts (proteins) of a virus that best stimulate your immune system. The Novavax COVID-19 vaccine contains harmless S proteins. It also has an ingredient called an adjuvant that helps with your immune system response.

Once your immune system recognizes the S proteins, this vaccine creates antibodies and defensive white blood cells. If you later become infected with the COVID-19 virus, the antibodies will fight the virus.

Protein subunit COVID-19 vaccines don't use any live virus and can't cause you to become infected with the COVID-19 virus. The protein pieces also don't enter the nucleus of your cells, where your DNA is kept.

Can a COVID-19 vaccine give you COVID-19?

No. The COVID-19 vaccines currently being developed and used in the U.S. don't use the live virus that causes COVID-19 . Because of this, the COVID-19 vaccines can't cause you to become sick with COVID-19 or shed any vaccine parts.

It can take a few weeks for your body to build immunity after getting a COVID-19 vaccination. As a result, it's possible that you could become infected with the virus that causes COVID-19 just before or after being vaccinated.

What are the possible general side effects of a COVID-19 vaccine?

Many people have no side effects from the COVID-19 vaccine. For those who get them, most side effects go away in a few days. A COVID-19 vaccine can cause mild side effects after the first or second dose, including:

  • Pain, redness or swelling where the shot was given.
  • Muscle pain.
  • Joint pain.
  • Nausea and vomiting.
  • Feeling unwell.
  • Swollen lymph nodes.

Babies ages 6 months through 3 years old also might cry, feel sleepy or lose their appetite after vaccination. Children in this age group also may have the common side effects seen in adults. These include pain, redness or swelling where the shot was given, fever, or swollen lymph nodes.

A healthcare team watches you for 15 minutes after getting a COVID-19 vaccine to see if you have an allergic reaction.

If the redness or tenderness where the shot was given gets worse after 24 hours or you're worried about any side effects, contact your healthcare professional.

Are there any long-term side effects of the COVID-19 vaccines?

The vaccines that help protect against COVID-19 are safe and effective. The vaccines were tested in clinical trials. People continue to be watched for rare side effects, even after more than 650 million doses have been given in the United States.

Side effects that don't go away after a few days are thought of as long term. Vaccines rarely cause any long-term side effects.

If you're concerned about side effects, safety data on COVID-19 vaccines is reported to a national program called the Vaccine Adverse Event Reporting System in the U.S. This data is available to the public. The CDC also has created v-safe, a smartphone-based tool that allows users to report COVID-19 vaccine side effects.

If you have other questions or concerns about your symptoms, talk to your healthcare professional.

Can COVID-19 vaccines affect the heart?

In some people, COVID-19 vaccines can lead to heart complications called myocarditis and pericarditis. Myocarditis is the swelling, also called inflammation, of the heart muscle. Pericarditis is the swelling, also called inflammation, of the lining outside the heart.

The risk of myocarditis or pericarditis after a COVID-19 vaccine is rare. These conditions have been reported after a COVID-19 vaccination with any of the three available vaccines. Most cases have been reported in males ages 12 to 39.

If you or your child develops myocarditis or pericarditis after getting a COVID-19 vaccine, talk to a healthcare professional before getting another dose of the vaccine.

Of the cases reported, the problem happened more often after the second dose of the COVID-19 vaccine and typically within one week of COVID-19 vaccination. Most of the people who got care felt better after receiving medicine and resting.

Symptoms to watch for include:

  • Chest pain.
  • Shortness of breath.
  • Feelings of having a fast-beating, fluttering or pounding heart.

If you or your child has any of these symptoms within a week of getting a COVID-19 vaccine, seek medical care.

Things to know before a COVID-19 vaccine

Are covid-19 vaccines free.

In the U.S., COVID-19 vaccines may be offered at no cost through insurance coverage. For people whose vaccines aren't covered or for those who don't have health insurance, options are available. Anyone younger than 18 years old can get no-cost vaccines through the Vaccines for Children program. Adults can get no-cost COVID-19 vaccines through the temporary Bridges to Access program, which is scheduled to end in December 2024.

Can I get a COVID-19 vaccine if I have an existing health condition?

Yes, COVID-19 vaccines are safe for people who have existing health conditions, including conditions that have a higher risk of getting serious illness with COVID-19 .

Your healthcare team may suggest you get added doses of a COVID-19 vaccine if you have a moderately or severely weakened immune system. Talk to your healthcare team if you have any questions about when to get a COVID-19 vaccine.

Is it OK to take an over-the-counter pain medicine before or after getting a COVID-19 vaccine?

Don't take medicine before getting a COVID-19 vaccine to prevent possible discomfort. It's not clear how these medicines might impact the effectiveness of the vaccines. However, it's OK to take this kind of medicine after getting a COVID-19 vaccine, as long as you have no other medical reason that would prevent you from taking it.

Allergic reactions and COVID-19 vaccines

What are the signs of an allergic reaction to a covid-19 vaccine.

You might be having an immediate allergic reaction to a COVID-19 vaccine if you experience these symptoms within four hours of getting vaccinated:

  • Swelling of the lips, eyes or tongue.

If you have any signs of an allergic reaction, get help right away. Tell your healthcare professional about your reaction, even if it went away on its own or you didn't get emergency care. This reaction might mean you are allergic to the vaccine. You might not be able to get a second dose of the same vaccine. However, you might be able to get a different vaccine for your second dose.

Can I get a COVID-19 vaccine if I have a history of allergic reactions?

If you have a history of severe allergic reactions not related to vaccines or injectable medicines, you may still get a COVID-19 vaccine. You're typically monitored for 30 minutes after getting the vaccine.

If you've had an immediate allergic reaction to other vaccines or injectable medicines, ask your healthcare professional about getting a COVID-19 vaccine. If you've ever had an immediate or severe allergic reaction to any ingredient in a COVID-19 vaccine, the CDC recommends not getting that specific vaccine.

If you have an immediate or severe allergic reaction after getting the first dose of a COVID-19 vaccine, don't get the second dose. But you might be able to get a different vaccine for your second dose.

Pregnancy, breastfeeding and fertility with COVID-19 vaccines

Can pregnant or breastfeeding women get the covid-19 vaccine.

If you are pregnant or breastfeeding, the CDC recommends that you get a COVID-19 vaccine. Getting a COVID-19 vaccine can protect you from severe illness due to COVID-19 . Vaccination also can help pregnant women build antibodies that might protect their babies.

COVID-19 vaccines don't cause infection with the virus that causes COVID-19 , including in pregnant women or their babies. None of the COVID-19 vaccines contains the live virus that causes COVID-19 .

Children and COVID-19 vaccines

If children don't often experience severe illness with covid-19, why do they need a covid-19 vaccine.

While rare, some children can become seriously ill with COVID-19 after getting the virus that causes COVID-19 .

A COVID-19 vaccine might prevent your child from getting the virus that causes COVID-19 . It also may prevent your child from becoming seriously ill or having to stay in the hospital due to the COVID-19 virus.

After a COVID-19 vaccine

Can i stop taking safety precautions after getting a covid-19 vaccine.

You are considered up to date with your vaccines if you have gotten all recommended COVID-19 vaccine shots when you become eligible.

After getting vaccinated, you can more safely return to doing activities that you might not have been able to do because of high numbers of people with COVID-19 in your area. However, if you're in an area with a high number of people with COVID-19 in the hospital, the CDC recommends wearing a well-fitted mask indoors in public, whether or not you're vaccinated.

If you have a weakened immune system or have a higher risk of serious illness, wear a mask that provides you with the most protection possible when you're in an area with a high number of people with COVID-19 in the hospital. Check with your healthcare professional to see if you should wear a mask at other times.

The CDC recommends that you wear a mask on planes, buses, trains and other public transportation traveling to, within or out of the U.S., as well as in places such as airports and train stations.

If you've gotten all recommended vaccine doses and you've had close contact with someone who has the COVID-19 virus, get tested at least five days after the contact happens.

Can I still get COVID-19 after I'm vaccinated?

COVID-19 vaccination will protect most people from getting sick with COVID-19 . But some people who are up to date with their vaccines may still get COVID-19 . These are called vaccine breakthrough infections.

People with vaccine breakthrough infections can spread COVID-19 to others. However, people who are up to date with their vaccines but who have a breakthrough infection are less likely to have serious illness with COVID-19 than those who are not vaccinated. Even when people who are vaccinated develop symptoms, they tend to be less severe than those experienced by unvaccinated people.

Are the new COVID-19 vaccines safe?

Andrew Badley, M.D., COVID-19 Research Task Force Chair, Mayo Clinic: The safety of these vaccines has been studied extensively. They've been tested now in about 75,000 patients in total, and the incidence of adverse effects is very, very low.

These vaccines were fast-tracked, but the parts that were fast-tracked were the paperwork; so the administrative approvals, the time to get the funding — those were all fast-tracked. Because these vaccines have such great interest, the time it took to enroll patients was very, very fast. The follow up was as thorough as it is for any vaccine, and we now have months of data on patients who received the vaccine or placebo, and we've compared the incidence of side effects between patients who received the vaccine and placebo, and that incidence of side effects, other than injection site reaction, is no different.

The side effects to the vaccines are very mild. Some of them are quite common. Those include injection site reactions, fevers, chills, and aches and pains. In a very, very small subset of patients — those patients who've had prior allergic reactions — some patients can experience allergic reaction to the vaccine. Right now we believe that number is exceedingly low.

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  1. Comprehensive literature review on COVID-19 vaccines and role of SARS-CoV-2 variants in the pandemic

    One study by Dan et al. showed that in patients infected with COVID-19, immunological memory to SARS-CoV-2 remained intact for up to 6 months. 3 Unfortunately, there is no long-term data on the duration of protected immunity against SARS-CoV-2 in patients after convalescence.

  2. Comprehensive literature review on COVID-19 vaccines and role of SARS

    Since the outbreak of the COVID-19 pandemic, there has been a rapid expansion in vaccine research focusing on exploiting the novel discoveries on the pathophysiology, genomics, and molecular biology of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.

  3. Real-world effectiveness of COVID-19 vaccines: a literature review and

    1. Introduction Globally, as of October 15, 2021, there had been more than 239.4 million confirmed cases of coronavirus disease 2019 (COVID-19), including over 4.8 million deaths ( WHO, 2021b ). Since the outbreak of COVID-19, several vaccines have been tested and granted emergency use authorization.

  4. COVID-19 Vaccine Hesitancy—A Scoping Review of Literature in High

    1. Introduction Since its first reported case in December 2019, the coronavirus-2019 (COVID-19) pandemic has culminated in nearly 179 million infections and 3.88 million deaths globally as of 24 June 2021 [ 1 ].

  5. Real-world effectiveness of COVID-19 vaccines: a literature review and

    PMID: 34800687 PMCID: PMC8595975 DOI: 10.1016/j.ijid.2021.11.009 Abstract Objective: To estimate the coronavirus disease 2019 (COVID-19) vaccine effectiveness (VE) against concerned outcomes in real-world settings. Methods: Studies reporting COVID-19 VE from August 6, 2020 to October 6, 2021 were included.

  6. Covid-19 Vaccines

    Review Article Franklin H. Epstein Lecture Covid-19 Vaccines — Immunity, Variants, Boosters Dan H. Barouch, M.D., Ph.D. Article Figures/Media Metrics 85 References 206 Citing Articles The...

  7. A Comprehensive Review of the Global Efforts on COVID-19 Vaccine

    The prior year has seen an unprecedented number of vaccine candidates directed at the COVID-19 pandemic. This report examines these vaccines and the related research effort, both traditional and forward-looking, to illustrate the advantages and disadvantages of their technologies, to denote the use of adjuvants and delivery systems in their application, and to provide a perspective on their ...

  8. SARS-CoV-2 vaccines strategies: a comprehensive review of ...

    Ortiz-Prado, E. et al. Clinical, molecular and epidemiological characterization of the SARS-CoV2 virus and the coronavirus disease 2019 (COVID-19), a comprehensive literature review. Diagn. Microbiol.

  9. Cochrane review of COVID-19 vaccines shows they are effective

    A comprehensive review of all the evidence available from randomised controlled trials of COVID 19 vaccines up to November 2021 has concluded that most protect against infection and severe or critical illness caused by the virus. The review, a collaboration of independent, international experts, also found there was little or no difference ...

  10. Long-term effectiveness of COVID-19 vaccines against infections

    This review, published in March, 2022, found a rapid reduction in protection against infections, but not against severe disease. However, the review only examined the vaccine effectiveness of primary vaccine series and did not report synthesised data on COVID-19-related mortality nor the omicron (B.1.1.529) variant.

  11. A systematic literature review to clarify the concept of vaccine

    53 Altmetric Metrics Abstract Vaccine hesitancy (VH) is considered a top-10 global health threat. The concept of VH has been described and applied inconsistently. This systematic review aims to...

  12. Frontiers

    View article impact REVIEW article Front. Immunol., 27 April 2022 Sec. Vaccines and Molecular Therapeutics Volume 13 - 2022 | https://doi.org/10.3389/fimmu.2022.843928 Vaccines for COVID-19: A Systematic Review of Immunogenicity, Current Development, and Future Prospects Zhan Zhang 1† Qi Shen 1,2† Haocai Chang 1,2*

  13. The vaccine journey for COVID-19: a comprehensive systematic review of

    Animal or in-vitro experimental studies were excluded. Moreover editorials, commentaries, abstracts, reviews, book chapters, and articles not in English were not included. Evidence synthesis: Our search identified 1359 published papers, 478 preprint articles and 367 ongoing clinical trials.

  14. Social media and attitudes towards a COVID-19 vaccination: A systematic

    Overall, the quality of the cross-sectional studies was moderate - 2 studies received 10 stars, 5 studies received 9 stars, 9 studies were evaluated with 8, 12 studies with 7,16 studies with 6, 11 studies with 5, and 6 studies with 4 stars. The included studies were categorized into four categories.

  15. PDF Review of Available Literature Related to COVID-19 Vaccine Development

    Review of Available Literature Related to COVID-19 Vaccine Development in the US Clinical and Preclinical Trials Phase 1 trial, Moderna/NIH mRNA vaccine https://www.nejm.org/doi/full/10.1056/NEJMoa2022483?query=TOC Interim results, Moderna/NIH mRNA vaccine: https://www.nejm.org/doi/full/10.1056/NEJMc2032195

  16. Frontiers

    Methods: A scoping review of literature between 1 January 2020 and 1 August 2021 was performed. ... Confusion due to the constant circulation of false news influences and increases the public's fear of side effects related to COVID-19 vaccines, raising additional questions and concerns about the vaccines. In 2018, 80% of respondents of the ...

  17. Efficacy and safety of COVID-19 vaccines: a systematic review

    Most of the COVID-19 vaccines appear to be effective and safe. Double-dose vaccination is recommended. However, more research is needed to investigate the long-term efficacy and safety of the vaccines and the influence of dose, age, and production process on the protective efficacy.

  18. Global research on RNA vaccines for COVID-19 from 2019 to 2023: a

    Introduction. Since 2019, the global COVID-19 pandemic has affected the lives of billions of people worldwide ().To deal with this situation, countries worldwide began to develop vaccines, including traditional inactivated vaccines, recombinant protein, live-attenuated vaccines, RNA vaccines, etc. (2-15).On October 2nd, 2023, the Nobel Assembly at the Karolinska Institutet decided to award ...

  19. PDF Next Generation COVID-19 Vaccines

    Scalability: The feasibility to rapidly manufacture next-generation platforms on a large scale is currently unclear. Vaccine effectiveness: Data on vaccine efficacy and real-world effectiveness against emerging variants is sparse and mostly from high-income nations. SARS-CoV-2 genome: A key bottleneck is the rapidly evolving mutational change in the SARS-

  20. COVID-19 vaccine acceptance and its associated factors in the Western

    Additionally, we used different, yet analogous, questions—COVID-19 vaccine acceptance and uptake—to measure vaccine endorsement at the two different time points. This was necessitated by the widespread rollout of COVID-19 vaccines in between these surveys, which would have complicated any question of intent among survey respondents as a whole.

  21. Understanding the role of risk preferences and perceptions in ...

    COVID-19 vaccines play a critical role in protecting against infection and transmission of the virus. Therefore, understanding public perceptions of COVID-19 vaccines is essential for successful ...

  22. Full article: Perceived impact of discussions with a healthcare

    Introduction. Vaccination is a safe and cost-effective way to prevent harmful diseases. Citation 1 It has been estimated that in the first year of the COVID-19 vaccination roll-out, 55.9% of the global population received at least one dose of COVID-19 vaccine, and that COVID-19 vaccines prevented up to 14 million deaths worldwide. Citation 2 However, some people consider COVID-19 vaccines with ...

  23. A Narrative Review of COVID-19 Vaccines

    PMID: 35062723 PMCID: PMC8779282 DOI: 10.3390/vaccines10010062 Abstract The COVID-19 pandemic has shaken the world since early 2020 and its health, social, economic, and societal negative impacts at the global scale have been catastrophic.

  24. Vaccines

    This systematic review critically evaluated the impact of a pre-infection COVID-19 vaccination on the incidence and severity of post-COVID-19 syndrome and aimed to assess the potential protective effect across different vaccines and patient demographics. This study hypothesized that vaccination before infection substantially reduces the risk and severity of post-COVID-19 syndrome. In October ...

  25. Heterogeneity in COVID-19 vaccine uptake within low-income minority

    The literature on disparities in COVID-19 vaccine uptake focuses primarily on the differences between White versus non-White individuals or differences by socioeconomic status. Much less is known about disparities in vaccine uptake within low-income, minority communities and its correlates. This study investigates disparities in COVID-19 vaccination uptake within racial and ethnic minoritized ...

  26. Cost-based COVID-19 vaccination and willingness to pay: A post-pandemic

    An examination of existing literature on willingness to pay for the COVID-19 vaccine prior to the official roll-out of mass COVID-19 vaccination Citation 45-59 indicates a spectrum of willingness to pay, with figures ranging from 49% in Nigeria Citation 24 and 53% in Pakistan, Citation 55 to as high as 78% in Indonesia Citation 52 and 80% in ...

  27. Literature review on COVID-19 vaccine efficacy in the immunocompromised

    Abstract Since the emergence of the virulent coronavirus in 2019, efforts to tackle the coronavirus-disease-2019 (COVID-19) pandemic have been made globally. The development of the coronavirus disease (COVID) vaccine was a significant breakthrough in ways to tackle the virus.

  28. A Systematic Review of the COVID Vaccine's Impact on the ...

    Aims & Objectives The objective of this study was to conduct a systematic review of research pertaining to the COVID-19 vaccine and its association with neurological complications.

  29. Get the facts about COVID-19 vaccines

    Staying up to date with a COVID-19 vaccine can:. Help prevent serious illness and death due to COVID-19 for both children and adults.; Help prevent you from needing to go to the hospital due to COVID-19.; Boost your body's protection, also called immunity, against catching the virus that causes COVID-19.; Be a safer way to protect yourself compared to getting sick with the virus that causes ...