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Technology – Research Article

A systematic and thematic analysis of the top 100 cited articles on mRNA vaccine indexed in Scopus database

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Article: 2135927 | Received 28 Jul 2022, Accepted 10 Oct 2022, Published online: 03 Nov 2022

ABSTRACT

The success of mRNA vaccines against SARS-CoV-2 implies that this technology can be applied to target any pathogen. However, the scientific production and research trends using the bibliometric method are still unknown. The top 100 most cited articles on mRNA vaccine research were obtained from the Scopus database from 1995 to 2021. Bibliometrix, an R-Package, and VOSviewer 1.6.11 were used for data analysis. There is a rapid growth in scientific outputs with a gradual increase in 2021. The United States produced 45 (45%) of the articles, followed by Germany with 15 (15%) and Israel with 10 (10%). The New England Journal of Medicine published the most papers in this field 13 (13%), followed by Nature 6(6%). Barney S. Graham was the most productive author among the top 100 most cited mRNA vaccine articles. University of Pennsylvania Perelman School of Medicine, US, was the top ranking institution, having 37 (37%). The visualization map clearly and spontaneously displayed the current state and research hot spots of mRNA research from a specific perspective. The most frequent keywords were COVID-19, vaccine, mRNA vaccine, mRNA, SARS-CoV-2, and immunogenicity, among others. A systematic review of the articles provided evidence that out of 100 articles, approximately 25 (25%) were focused on vaccine production and evaluation, followed by 26 (26%) in mRNA vaccine safety and efficacy, 23 (23%) were into mRNA vaccination, 23 (23%) considered risk factors associated with mRNA vaccination, while 8 (8%) of the articles covered the issue of mRNA vaccine delivery. In addition, 42% of the articles focused on COVID-19, 17% on cancer, 8% on influenza virus, 4% on COVID-19 and kidney disease, 3% COVID-19 and myocarditis, and 3% on rabies virus, among others. The findings of this systematic and thematic analysis provided the knowledge basis for further research on mRNA vaccines globally.

Introduction

Vaccines induce immune responses by simulating the infection process inside the human body and enabling it to develop lasting immunity. When the body is re-exposed to the target antigens, it can produce antibodies that neutralize the antigens and therefore prevent infection.Citation1 Research conducted by Louis Pasteur in the 19th century resulted in the discovery of attenuated pathogens that were inoculated into a subject, to prevent them from infection when exposed to the same pathogen.Citation2

The mRNA vaccines represent a potentially disruptive technology for the vaccine industry.Citation3 Messenger RNA is produced by in vitro reactions with recombinant enzymes, ribo-nucleotide triphosphates, and a DNA template; thus, it is rapid and relatively simple to produce compared with the others were vaccine production platforms.Citation4 A co-formulation of the mRNA of the RNA is encapsulated in lipid nanoparticles that protect the RNA strands and help their absorption into the cells. Upon delivery, cells will take up the mRNA and translate it into protein in situ. The individual’s immune system will then mount a robust adaptive immune response against the target protein.Citation5

Most works with mRNA vaccine were done with cancer,Citation4 and infectious diseases caused by Zika virus, the dengue virus, the respiratory syncytial virus, HIV, influenza H7N9 and Flavivirus,Citation6 and interestingly noninfectious diseases such as diabetes.Citation3 The first mRNA vaccine against an infectious disease that was evaluated in humans targeted the rabies virus, and a clinical trial showed that it elicited functional antibodies.Citation7 The success of mRNA vaccines against SARS-CoV-2 implies that this technology can target any pathogen for which a protein can be identified as an antigen that elicits protective immunity.Citation8

Messenger RNA vaccines have several advantages over conventional vaccines since they do not integrate into the host genome.Citation4 A single mRNA vaccine can encode multiple antigens, strengthening the immune response against resilient pathogens Citation9 and enabling the targeting of multiple microbes or viral variants with a single formulation.Citation10 The simplicity of in vitro transcription of mRNA suggests the potential for fast, scalable, and low-cost manufacturing.Citation11

Many researchers in medical and other scientific fields have used the concept of bibliometrics. Thus, researchers have used both the Web of Sciences and Scopus databases, followed by a quantitative analysis based on mathematical statistics to quantitatively reflect the research hotspots and reveal the future trends of new theories.Citation1–12Citation25 So far, although there are many articles published on mRNA vaccines globally, no study on the top 100 most cited articles on mRNA vaccines has been conducted. Hence, this study aimed to provide a comprehensive analysis using a systematic and thematic analysis of the top 100 most cited articles published in mRNA vaccine research via analyzing the global publishing landscape, author, and country performance of publications related to mRNA vaccine research retrieved from the Scopus database. Based on developmental trend of mRNA vaccine trends, this paper proposed the aspects that need further study in the future, which may provide a reference for researchers in raising awareness of potential research gaps and research collaboration toward the development of mRNA vaccines to control infectious diseases.

Methods

Study design

A descriptive bibliometric study using a systematic and thematic analysis was performed to evaluate the top 100 most cited articles on global mRNA vaccines through a quantitative analysis.

Study participants

No human subjects were directly involved in this study. The metadata included in the study was searched and collected from the Scopus database (https://www.scopus.com/). Online databases provide an extensive, comprehensive, and multidisciplinary core journal citation index database. The comprehensive online bibliographic database reported in the study was accessed via the electronic library of Southeast University, Nanjing, China.

Publications’ timespan

The top 100 most cited articles in the mRNA vaccine were identified matching the search criteria and were published from 1995 to 2021.

Data sources and search strategy

The data used in this study were extracted from the Scopus database. The search was conducted on September 18, 2022, using the boolean operators such as “AND” or “NOT,” to ensures that we gather accurate information related to the top 100 most cited articles on mRNA vaccine indexed in the Scopus database:

The following search was conducted using the query search as (TITLE (mrna AND vaccine*) OR TITLE (mrna AND vaccination*) OR TITLE (mrna AND vaccine*)) AND (EXCLUDE (PUBYEAR, 2022) OR EXCLUDE (PUBYEAR, 1994)) AND (LIMIT-TO (DOCTYPE, “ar”)) AND (LIMIT-TO (LANGUAGE, “English”))

In total, 733 mRNA publications retrieved were within the Timespan: 1995 to December 31, 2021, and then the top 100 cited articles in mRNA were selected based on the citation times. The raw data was exported into BiB text, comma-separated value (csv) excel, or RIS file format for further in-depth statistical analysis. Finally, the top 100 cited articles on mRNA vaccine were comprehensively analyzed based on the bibliographical information (). The retrieved mRNA data included citation information, bibliographical information, annual trend per year, author’s country or region, source publication, the collaboration between author and countries, institution, and keywords (author keyword, keyword Plus, and Abstract) were analyzed using bibliometric tools. The journal Impact factor (JIF) was determined by the Journal Citation Report 2021. The current study does not require ethical approval and, like other bibliometric analyses, used secondary data without any human participants.

Figure 1. Prisma flow diagram of the publication on top 100 cited articles on mRNA vaccine.

Figure 1. Prisma flow diagram of the publication on top 100 cited articles on mRNA vaccine.

Bibliometric analysis

Data were analyzed using the open-source R. Studio software (www.rstudio.com), version 4.0.5, and bibliometrix, an R-Package,Citation26 VOSviewer 1.6.11 software was used to create authorship co-occurrence network by units of authors and countries.Citation27 The thickness shown in the VOSviewer mapping, specifically the connecting lines between nodes represents the degree of connection between authors or countries. The thicker the line, the stronger the connection.Citation28,Citation29 In addition, current approaches and directions for future research and main contributions to mRNA vaccine are summarized.

Results

Basic characteristics of the data

The annual number of the top 100 most cited articles in mRNA vaccine was published between 1995 and 2021 (). The scientific publications of the top 100 most cited mRNA vaccines have increased gradually after the year 2020 (). Overall, the retrieved articles received a total of 309.7 average citations per documents, with an annual growth rate of 16.9%. The articles were published in 48 journal sources, contributed by 3107 authors, 37.3% coauthors per documents, and 40% international co-authorship. The other characteristics of current mRNA vaccine research outputs are summarized in .

Table 1. The top 100 cited articles on the mRNA vaccine.

Figure 2. Annual number of articles and Mean of Total Citations per Year (Mean TCPY) of top 100 cited articles on mRNA indexed in Scopus database from 1995 to 2021.

Figure 2. Annual number of articles and Mean of Total Citations per Year (Mean TCPY) of top 100 cited articles on mRNA indexed in Scopus database from 1995 to 2021.

Figure 3. Basic characteristics of the top 100 most cited articles on mRNA vaccine.

Figure 3. Basic characteristics of the top 100 most cited articles on mRNA vaccine.

The top 100 most cited articles

The top 100 cited articles on mRNA were published from 1995 to 2021, with citation range (83 to 5757) times.Citation7–30Citation54–56Citation62–65Citation67–69Citation72–104Citation106–108Citation116–118Citation128 The article titled “Safety and efficacy of the BNT162b2 mRNA COVID-19 vaccine” by Polack F.P., et al. 2020 published in the New England Journal of Medicine was the top cited article cited 5757 times.Citation30 However, the article “Efficacy and safety of the mRNA-1273 SARS-CoV-2 vaccine” by Baden L.R., et al. 2021 published in the same journal was ranked second, receiving 3768 citations Citation31 as presented in ().

Authorship impact on mRNA vaccine research

Out of the 3107 authors who contributed to the top 100 most cited articles, only authors with ≥5 h_index () and authors with over 6000 citation times of articles are presented in . The analysis of authors shows Barney S Graham from Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, USA, was the most productive author in this field with eight publications, followed by Hamilton Bennett from Moderna, Inc., Cambridge, United States, Cambridge, USA, with 7 articles, and Brett Leav from Brigham and Women’s Hospital, Boston, and Moderna, Cambridge, USA, with 7 articles (). Barney S. Graham was the most influential authors among the top 100 most cited mRNA vaccine research based on the number of classical citations with 7967 citations ().

Table 2. The top most productive authors with ≥5 articles.

Table 3. The top most influence authors with over 6000 citation times.

Authorship pattern analysis

Analysis of the authorship pattern on the top 100 most cited articles on mRNA vaccine based on the frequency of publication by authors was described using Lotka’s law (). From the figures, the proportion of all authors based on the number of documents written, 85.84% publish only one article, 10.43% publish two articles, 2.51% publish three articles, and so on a ccording to Lotka’s law.

Figure 4. Frequency analysis of number of publications written by authors (a), and proportions of Authors in mRNA vaccine using Lotka’s law.

Figure 4. Frequency analysis of number of publications written by authors (a), and proportions of Authors in mRNA vaccine using Lotka’s law.

Analysis of the top productive Journals

According to quantitative analysis, a total of 48 journal sources were reported publishing the top 100 cited articles in mRNA vaccine. The New England Journal of Medicine published 13 articles and cited 15,072 times. The core journals with high recognition in this field can be determined by the researcher to publish their work or search for the articles relevant to mRNA vaccine ().

Table 4. Source local impact with three or more than in mRNA vaccine.

Corresponding author’s country

Of 18 countries that contributed, only the authors with 2 or more articles were reported (). The United States is the top leading country in the top 100 most cited mRNA vaccine research with 45 articles, followed by Germany with 15 articles, and Israel with 10 articles. In addition, the USA, Germany, and Israel were also the most influential in mRNA research based on the number of classical citations reported globally.

Table 5. Corresponding Author’s Country and its Citations.

Top productive institutions in mRNA vaccine

Studies on mRNA vaccines were contributed by 463 different authorship institutions listed in . The leading productive institutions are the University of Pennsylvania Perelman School of Medicine, with 37 articles, and followed by Washington University School of Medicine with, 15 articles, and Vanderbilt University Medical Center with 15 articles, among others ().

Table 6. The top productive institutions in mRNA vaccine research with six or more articles.

Research frontiers based on the keyword

The keywords used by the authors indicate the content of the articles. Visual representation of word frequency was carried out using R-studio, and Word clouds were used to analyze the underlying patterns in the text. From the mapping, we identified that the top Keywords Plus in mRNA vaccine were “Female” (133), “male” (102), “adult” (99), “article” (92), “human” (89), “vaccination” (85), “middle-aged” (80), “RNA” (79), “aged” (78), “messenger RNA” (78) as presented in . Additionally, the top-frequency Author’s Keywords were “COVID-19” (14), “Vaccine” (9), “mRNA vaccine” (7), “SARS-CoV-2” (7), “Immunogenicity” (5), “vaccination” (5), “lipid nanoparticle” (4), and “dendritic cell,” among others, as presented in .

Figure 5. Visualization text analysis results with Word Clouds summarizing the top 100 most commonly mRNA Keywords plus provided by Journal (a), and Author’s Keywords (b).

Figure 5. Visualization text analysis results with Word Clouds summarizing the top 100 most commonly mRNA Keywords plus provided by Journal (a), and Author’s Keywords (b).

Furthermore, to identify the relationships between topics, the verification was done through Multiple correspondence analysis (MCA) that used dimensionality reduction techniques to draw a conceptual structure map of the 75 Keywords in the mRNA field. This is shown as 5 clusters with the five different colors to show the association between the published topics having similar common concepts ().

Figure 6. Conceptual Structure Map-Multiple Correspondence Analysis (MCA) method of 75 Keywords Plus reported in top 100 most cited articles on mRNA vaccine.

Figure 6. Conceptual Structure Map-Multiple Correspondence Analysis (MCA) method of 75 Keywords Plus reported in top 100 most cited articles on mRNA vaccine.

Conceptual structure analysis

A variety of themes form the foundation of the mRNA vaccine research field. A comprehensive analysis of the themes of the mRNA was carried out using a thematic map. This strategy combines performance analysis and scientific mapping tools to detect and visualize conceptual subdomains. We used the Author’s Keywords (), keywords plus (), and Title () to generate the thematic map and set three parameters to maintain the richness of information on m RNA vaccine without impairing map readability. The algorithm built the map from the 250 most frequent Author keywords, Keywords Plus, and Title considering only keywords with a minimum frequency of three occurrences per 1,000 documents, with a limit of three keywords for each cluster. The algorithm formed nine clusters in Authors Keywords, three clusters in Keywords Plus, and seven clusters in tiles dispersed in the thematic map.

Figure 7. Thematic Analysis map develop by using Conceptual structure for Author’s Keywords (a), Keyword Plus (b), and Keywords extracted from title (c), clusters produced by Louvain clustering algorithm.

Figure 7. Thematic Analysis map develop by using Conceptual structure for Author’s Keywords (a), Keyword Plus (b), and Keywords extracted from title (c), clusters produced by Louvain clustering algorithm.

The figure shows the development of the topic into four quadrants comprising the following: first quadrant (top right): motor-themes, both important and well developed; the second quadrant (top left): Niche themes or highly development and isolated themes, which have developed well but the topic reported on the current mRNA vaccines; the third quadrant (bottom left): emerging topic or disappearing themes for mRNA vaccine research; and the fourth quadrant (bottom right): basic themes or basic and transversal Themes, which is important to the field mRNA vaccine research but not well-developed ().

Co-authorship relations among authors

We used the features of the VOSviewer software to create co-occurrence networks, which reported co-authorship by units of authors and countries () of 3107 authors who contributed to the top 100 cited articles, and a minimum of 2 documents from each author were chosen, resulting in 98 meeting the threshold. Only 52 authors were distributed across five clusters highlighted in different colors, with links between authors (L = 193) and total link strength (TLS = 299). Additionally, in , 18 countries were reported and 2 minimum number of documents were chosen, resulting in 19 countries distributed across six clusters, with links between authors (L = 49) and total link strength (TLS = 110).

Figure 8. Co-authorship by unit of authors (a), and countries (b) based on Links (L) Total Links Strength (TLS).

Figure 8. Co-authorship by unit of authors (a), and countries (b) based on Links (L) Total Links Strength (TLS).

A systematic review of the top 100 most cited articles identified on mRNA vaccine

The objectives and the main findings of the top 100 cited articles on mRNA vaccine are summarized in . Among the top 100 most cited articles, 25% were related to vaccine production and evaluation,Citation35–37Citation40–42,Citation43–48Citation51–54Citation56–58Citation61–66Citation77–91Citation94–103Citation108–116Citation118,Citation119-121Citation123 followed by 23% to safety and efficacy of the vaccine,Citation7–30Citation34–41Citation44,Citation45-49Citation50-65Citation67-69Citation74-83Citation85-87Citation89-92Citation93-113Citation115-120Citation124 20% to vaccination,Citation36–46Citation52,Citation53-57Citation59-76Citation78-80Citation81-86Citation88-90Citation96-97Citation100-104Citation111-125Citation128 16% to risk factors associated with vaccination,Citation47,Citation60,Citation62,Citation72,Citation73,Citation75,Citation79,Citation82,Citation95,Citation98,Citation99,Citation101,Citation102,Citation106,Citation109,Citation110,Citation112,Citation114 and 11% of the published articles were focused on the issue of vaccine delivery.Citation55,Citation63,Citation64,Citation68,Citation71,Citation105,Citation107,Citation117

Table 7. Systematic analysis of the top 100 cited articles on mRNA.

The top 100 cited articles indicated that the monoclonal antibodies elicited by the mRNA-1273 vaccines potently neutralize SARS-CoV-2.Citation77,Citation91 Nucleoside-modified mRNA-LNPs elicit rapid and durable protective immunity against the Zika virus.Citation103 The human respiratory syncytial virus is a possible vector for protective antigens in another respiratory tract and might have utility in transient gene therapy of the respiratory tract.Citation35 LNP-formulated, modified mRNA vaccines can induce protective immunogenicity with acceptable tolerability profiles against the influenza virus.Citation118 Self-amplifying RNA is a promising platform for vaccines against viral diseases.Citation74 The treatment effect of autoimmune encephalomyelitis is associated with a reduction of effector T cells and the development of regulatory T cell (Treg cell) populations.Citation43 RNA tumor antigen vaccine strategy has potential applications for human cancer treatment and prevention.Citation47 The feasibility of a non-replicating mRNA rabies vaccine in small and large animals highlights the promise of mRNA vaccines for the prevention of infectious diseases.Citation98 In addition, mRNA/LNP is a versatile platform that enables the development of vaccination strategies that could prevent cytomegalovirus infection and consequent disease in different target populations.Citation102

The safety and efficacy of the mRNA vaccine showed that a two-dose regimen of BNT162b2 conferred 95% protection against COVID-19 in persons 16 years of age or older.Citation54,Citation66 While the mRNA-1273 vaccine showed 94.1% efficacy at preventing COVID-19 illness, including severe disease.Citation58 Women who are vaccinated with COVID-19 vaccine at later times during early pregnancy have less time during which they are at risk for pregnancy loss.Citation121 The antibody-mediated response to the BNT162b2 mRNA covid-19 vaccine in patients with CLL is markedly impaired and affected by disease activity and treatment.Citation31 A prophylactic mRNA-based candidate vaccine can induce functional antibodies against a viral antigen when administered with a needle-free device. The vaccine was generally safe with a reasonable tolerability profile.Citation7 The first mRNA vaccines against H10N8 and H7N9 influenza viruses were well tolerated and elicited robust humoral immune responses.Citation50 The self adjuvant RNActive® vaccine CV9103 was well tolerated and immunogenic.Citation96 The self incidence of myocarditis, although low, increased after the receipt of the BNT162b2 vaccine, particularly after the second dose among young male recipients.Citation86 Vaccination of guinea pigs induced EBOV-specific IgG and neutralizing antibody responses and 100% survival after EBOV infection.Citation129

The authorized mRNA COVID-19 vaccines effectively prevented SARS-CoV-2 infection, regardless of symptom status, among working-age adults in real-world conditions.Citation49,Citation94,Citation119 The establishment of autologous glioblastoma stem cells (GSCs) cultures under reasonable manufacturing procedures (GMP) is feasible, and the vaccination against GSCs is safe, well-tolerated, and may prolong recurrence-free survival.Citation67 A third dose of the BNT162b2 mRNA vaccine effectively protects individuals against severe COVID-19-related outcomes, compared with receiving only two doses at least 5 months ago.Citation85 Therapeutic vaccination with autologous TriMix-DC is feasible, safe, and immunogenic and can be combined with sequential IFN-a-2b.Citation90,Citation124 The COVID-19 vaccine was immunogenic in pregnant women, and the vaccine elicited antibodies that were transported to infant cord blood and breast milk.Citation44 The feasibility of vaccination with DCs loaded with mRNA encoding a defined antigen identified of immunogenic T-cell epitopes. This type of vaccination provides an opportunity for direct and fast discovery of novel T-cell epitopes from any tumor-specific or tumor-associated antigen.Citation110

The risk factors associated with mRNA vaccination were significantly lower and associated with previous infection, gender, age, ethnicity, job role, and Index of Multiple Deprivation score. BNT162b2 vaccine can prevent symptomatic and asymptomatic infection in working-age adults.Citation123 The potential for rare vaccine-related adverse events must be considered in the context of the well-established risk of morbidity, including cardiac injury, following COVID-19 infection.Citation60,Citation75,Citation87 Cladribine treatment does not impair the humoral response to COVID-19 vaccination.Citation93,Citation97 mRNA BNTb262 vaccine was immunogenic in the majority of patients with AIIRD, with an acceptable safety profile. Treatment with glucocorticoids, rituximab, MMF, and abatacept was associated with a significantly reduced BNT162b2-induced immunogenicity.Citation113 Most kidney transplant recipients remain at high risk for COVID-19 despite vaccination.Citation68,Citation72,Citation79,Citation115 The incidence of serious outcomes, including acute myocardial infection, Bell palsy, cerebral venous sinus thrombosis, Guillain-Barre syndrome, myocarditis/pericarditis, pulmonary embolism, stroke, and thrombosis with thrombocytopenia syndrome was not significantly higher at 1–21 days post-vaccination compared with 22–42 days post-vaccination.Citation88 Different strategies may need to be explored in patients with IMID taking methotrexate to increase the chances of immunization efficacy against SARS-CoV-2 as has been demonstrated for augmenting immunogenicity to other viral vaccines.Citation107

Among the potential non-viral vectors, lipid nanoparticles are particularly promising for vaccine delivery in cancer.Citation34 Direct injection of protamine-protected mRNA is feasible and safe.Citation41 Treatment with naked mRNA results in protein expression is feasible and safe. Furthermore, an increase in antitumor humoral immune response was seen in some patients.Citation83 Administration of globin UTR-stabilized mRNA is a versatile vaccination strategy that can be manipulated to fit the requirement of antiviral, antibacterial, or antitumor immunity.Citation46 The observed tumor immunity correlates with splenic antigen-specific CD81 T cells and is achieved only when mRNA is delivered in nanoparticles but not in naked format.Citation114

Discussion

The current study provided an overview of the top 100 cited articles on mRNA vaccine globally from documents indexed in the Scopus database for the first time. Scopus is one of the most appropriate online databases widely used for bibliometric analysis. The study revealed a clear interest in mRNA research productivity in the year 2021. This may be owed to the outbreak of COVID-19 pandemic. The study used R software to provide the researcher with mRNA vaccine author’s productivity by using Lotka’s Law as one of the classical laws of bibliometrics to examine the distribution of frequency of the researcher’s publications as well as reports in other scientific fields.Citation130 Thus, findings would be of interest to the scientific community to demonstrate the general applicability of this relation to authors in mRNA vaccine top cited articles and their author’s productivity in the subject.Citation70,Citation131

The study highlights that the top-rank paper was Safety and efficacy of the BNT162b2 mRNA COVID-19 vaccine, published in 2020 in the New England Journal of Medicine. The article indicated that a two-dose regimen of BNT162b2 conferred 95% protection against COVID-19 in persons 16 years of age or older. Due to the COVID-19 pandemic, this article became the most influential with 5757 citations.Citation54 Graham BS and Bennett H were considered as the most influential authors reported in the top 100 most cited mRNA vaccine. According to Lotka’s law, only 0.3% percent of the authors in a given field produced more than 5 articles.

The New England Journal of Medicine published the most mRNA vaccine papers. This journal is the most pioneer journal in medical research, which publishes high-quality research. mRNA vaccine research was conducted by the developed countries because they own the most potential funding agencies that fund scientific research. As previously reported, funding is one of the potential mechanisms to encourage and increase productivity.Citation18 Keyword analysis indicated that the top-cited articles on mRNA vaccine covered various key aspects, including COVID-19, vaccine, mRNA vaccine, mRNA, SARS-CoV-2, and immunogenicity, among others. Evidence from the network analysis reveals a significant level of collaboration among authors in the field, as shown in the clusters. The collaboration is vital as it enables the sharing of knowledge and findings of scientific research, such as genome sequences and the possible development of the mRNA vaccine.

The mRNA vaccine articles were classified into vaccine production and evaluation, safety and efficacy of the vaccine, vaccination, risk factors associated with vaccination and vaccine delivery system. Meanwhile, the most cited articles were focused on COVID-19, followed by cancer, influenza virus, COVID-19 and kidney diseases, COVID-19 and myocarditis, and rabies virus, among others.

This study has limitations that related to its theme’s diversity. The methodology always emphasizes the most statistically most relevant themes, but we do not represent all the themes of the research field, in addition the study only provides statistics based on the number of articles and highest citation, whereas the contribution of other excellence researchers in the field was not shown in the current analysis. We use only one database (Scopus); thus, there is the possibility of missing out on key top-cited articles that may be available in other databases such as Web of Sciences, PubMed, and Google Scholar. Therefore, the results of the current assessment might not be comprehensive. Furthermore, we only consider full research articles as inclusion criteria for the purpose of the analysis. Thus, with the inclusion of all documents in the research field, the results could be a little different. Future studies could discuss and improve the methodological strategy adopted and provide a comprehensive analysis to show the contribution of at least 100 most impact authors in the field. In addition, the presence of false-positive and false-negative results must be regarded as in any bibliometric study. Other limitations, were that we only included studies published in the English language and underestimated studies published in other languages, which may also have higher citation scores than the ones we extracted.

Above all these limitations, the results consolidate the recent knowledge on mRNA vaccines and will prove helpful for researchers to understand the top 100 most cited articles based on their themes and systematic analysis.

Conclusions

The study provides quantitative and qualitative analyses of the top 100 most cited articles on mRNA vaccine. The annual number of articles has steadily increased between 2020 and 2021. The comprehensive analysis also provides insights into scientific research productivity by authors, countries, and institutions, which will assist in generating evidence-based descriptions, comparisons, and mapping visualizations of research output in mRNA vaccines. In addition, the study provides a road map of the characteristics of the top 100 most cited articles and extensively describes their patterns of performance and the impact of mRNA vaccine research, core journals, and corresponding author’s countries, and other information that can be a useful and helpful tool for future studies.

Application and future research directions

The current analysis provides readers with applied evidence and gap maps on top 100 most cited articles on mRNA vaccine, providing a visual representation of the conceptual structure analysis of research based on the mapping analysis. Moreover, the study also provides a scientific relationship between researchers and countries toward research collaboration to enhance research on mRNA vaccines. Through a comprehensive analysis of co-authorships, our study provides an insight into partners in research endeavors and describes the scientific network. Furthermore, the qualitative analysis of the keywords helps to identify the current focus and future research direction within mRNA vaccine research. Through the thematic analysis, the current investigation was able to use conceptual structure analysis to describe patterns across qualitative data on the reported topic on specific themes (motor-themes, Niche themes, emerging topics or disappearing themes, and basic themes or basic and Transversal Themes) based on the Relevance Degree (Centrality) and Degree (Density) in the vertical and horizontal axis.

Data access

All data presented in this article can be retrieved from Scopus using keywords listed in the methodology.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The study was funded by the Chinese Academy of Sciences Presidents International Fellowship Initiative (Grant No.2021VBA0008)

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