Current and Future Perspectives on the COVID-19 Vaccine: A Scientometric Review

This study attempted to draw the present and future perspective of the COVID-19 vaccine by identifying the most important scientists and their scientific contexts, trends of research topics, and relationships between different entities. Methods: To achieve this purpose, bibliometric and scientometric techniques were used to analyze 6288 scientific documents contributing to COVID-19 vaccines from the beginning of 2019 to 13 December 2021, indexed in the Web of Science. Results: The United States (US) had the greatest impact by publishing 2104 documents and receiving 32,958 citations. The US and the UK countries had the highest level of scientific collaborations with 192 collaborative studies. The University of Oxford and the Harvard Medical School were the most active institutions, and the University of Oxford and Emory University were the most influential institutions. Pollard AJ and Lambe T had the most publications and the highest citations and h-index. T Lambe, SC Gilbert, M Voysey, and AJ Pollard from the University of Oxford had the highest number of co-authorships. More than 19% of the research was conducted in the field of immunology. The Vaccines journal had the most publications, with 425 articles. The US Department of Health & Human Services granted the most research. In 2019, studies were focused on the topics of COVID-19 virus identification and ways to deal with it; in 2020, studies focused on the topics of COVID-19 and vaccines, whereas in 2021, they focused on the topics of COVID-19 vaccines and their effects, vaccines hesitancy, the role of healthcare workers in COVID-19, as well as discussions about these vaccines in the social media. Conclusions: Recognition of the most important actors (countries, institutes, researchers, and channels for the release of COVID-19 vaccine studies), research trends, and fields of study on the COVID-19 vaccine can be useful for researchers, countries, and policy makers in the field of science and health to make decisions and better understand these vaccines.


Introduction
The new coronavirus, or COVID-19, is a deadly virus common between humans and animals [1], which was identified by the World Health Organization on 11 March 2020, as a pandemic [2]. The pandemic showed that it is not only a medical problem. Since the pandemic affects society as a whole, new research frameworks are needed, including to analyze studies focused on the COVID-19 vaccines, not the COVID-19 or coronavirus. On the other hand, the reference of the present study to the current and future research fields of studies on the COVID-19 vaccines is another distinguishing point of this research from other studies.

Materials and Methods
According to the objectives of the present research, the method of bibliometric and scientometric analysis was used to analyze scientific publications on the COVID-19 vaccines. The population of this research consists of all documents on the COVID-19 vaccines from 2019 to 13 December 2021 indexed in the Web of Science database. The methodology of this research was divided into two parts, which are described in detail below.

Data Retrieval
The search strategy was such that in the first step, the Clarivate Analytics Web of Science (WoS) Core Collection was selected [20,21]. Next, the three citation indexes of this database, i.e., SCI-EXPANDED, SSCI, and A&HCI indexes, became the basis of the research. Different names of COVID-19, along with the two words vaccine and vaccination, were searched to collect the documents through the Advanced Search of the WoS, as well as the scientific and common names of different types of vaccines (See Appendix A) in the field of TOPIC (TS phrase in Web of Science) without any restrictions on the TYPE and LANGUAGE of the documents. The search strategy of this study led to the retrieval of 6288 records (See Figure 1), all records were extracted in plain text format in batches of 500 in 13 TXT files and saved on a personal computer; then, all the files were merged into one file for ease in analyzing.

Data Analysis
All extracted files were analyzed using HistCite (v. 12  In other words, the website of COVID-19 vaccines www.track.org was used (19 January 2022) to gather information about the type of vaccine, primary developers, and status of approving countries. Additionally, information on the doses purchased from each vaccine was collected from the app.powerbi.com website. The website www.RAPS.org (accessed on 19 January 2022) was also used to identify vaccine-producing countries.

Data Analysis
All extracted files were analyzed using HistCite (v. 12.03.17, Philadelphia, PA, USA), Publish or Perish (v. 8, London, UK), VOSviewer (v. 1.6.17, Leiden, The Netherlands), CiteSpace (v. 5.8.R3, Philadelphia, PA, USA), and Bibliometrix R Package software (v. 3.1.4, Naples, Italy). The analysis process was such that the capabilities of HistCite software were used to analyze information about authors, institutions, countries, and journals [20]. In addition, Bibliometrix R Package was used to draw the maps of geographical distribution, three-field plot, and the process of publishing journals. While VOSviewer was used to determine the status of scientific collaborations between researchers, organizations, and institutions conducting research on the COVID-19 vaccines. Finally, CiteSpace was used to review the research process on the COVID-19 vaccines, as well as the timeline map of countries and institutions in this field.    Table 1 show the co-authorship network and details of the most active authors in COVID-19 vaccine studies. More than 32,800 authors co-authored publications on vaccines. Table 1 lists the authors who have published at least 18 documents in this field. In Figure 3, the nodes represent the authors and links indicate the number of coauthorships formed between the authors. Furthermore, the researchers who collaborated on at least three studies are shown in Figure 3. This network consists of 1491 nodes and 5834 links. T Lambe, SC Gilbert, M Voysey, and AJ Pollard from the University of Oxford had the highest number of co-authorship. According to Table 1, Pollard AJ and Lambe T published most of the publications in this field and are located in the first and second places. However, Pollard AJ and Lambe T, with 3583 and 3579 citations, which are in the first and second places in terms of scientific publications in this field, were able to obtain the highest citation rate and H-index score among their peers. The important point in Table 1 of the year of publication of the authors' documents is that Wiwanitkit V, with the publication of 23 documents in 2021, is the only active author who has been able to publish this number of documents in this period.   Table 1 show the co-authorship network and details of the most active authors in COVID-19 vaccine studies. More than 32,800 authors co-authored publications on vaccines. Table 1 lists the authors who have published at least 18 documents in this field. In Figure 3, the nodes represent the authors and links indicate the number of co-authorships formed between the authors. Furthermore, the researchers who collaborated on at least three studies are shown in Figure 3. This network consists of 1491 nodes and 5834 links. T Lambe, SC Gilbert, M Voysey, and AJ Pollard from the University of Oxford had the highest number of co-authorship. According to Table 1, Pollard AJ and Lambe T published most of the publications in this field and are located in the first and second places. However, Pollard AJ and Lambe T, with 3583 and 3579 citations, which are in the first and second places in terms of scientific publications in this field, were able to obtain the highest citation rate and H-index score among their peers. The important point in Table 1 of the year of publication of the authors' documents is that Wiwanitkit V, with the publication of 23 documents in 2021, is the only active author who has been able to publish this number of documents in this period.   Index  NP  TC  PY_Start  1  Pollard AJ  13  36  17  36  3583  2020  2  Lambe T  13  29  18  29  3579  2020  3  Gilbert SC  11  24  16  24  3238  2020  4  Baden LR  4  23  6  23  1823  2020  5  Wiwanitkit V  1  4  1  23  21  2021  6  Voysey M  10  22  13  22  3210  2020  7  Temsah MH  3  4  4  20  19  2021  8  Terpos E  6  10  11  20  118  2021  9  Halwani R  3  3  4  19  14  2021  10 Klimek L  4  8  8  19  81  2021  11  Dimopoulos MA  6  10  10  18  115  2021  12  Hotez PJ  8  18  12  18  400  2020  13  Talbot HK  10  18  13 18 599 2020 Figure 4 illustrates a three-field plot in the research on the COVID-19 vaccines, focusing on the relationships between authors, countries, and keywords. In Figure 4, rectangles represent each entity (authors on the left, countries in the middle, and keywords on the right). The height of the rectangles refers to the number of studies conducted by countries, authors, and research fields, and the greater the number of studies by each of these entities, the size and height of the rectangles will be more. Lines of communication also reflect the links made between authors and countries, as the more research that was conducted by authors and countries on the subject, the thickness of the links will be greater.

Rank
Authors H-Index G-Index HC-Index NP TC PY_Start   1  Pollard AJ  13  36  17  36  3583  2020  2  Lambe T  13  29  18  29  3579  2020  3  Gilbert SC  11  24  16  24  3238  2020  4  Baden LR  4  23  6  23 1823 2020  Figure 4 illustrates a three-field plot in the research on the COVID-19 vaccines, focusing on the relationships between authors, countries, and keywords. In Figure 4, rectangles represent each entity (authors on the left, countries in the middle, and keywords on the right). The height of the rectangles refers to the number of studies conducted by countries, authors, and research fields, and the greater the number of studies by each of these entities, the size and height of the rectangles will be more. Lines of communication also reflect the links made between authors and countries, as the more research that was conducted by authors and countries on the subject, the thickness of the links will be greater.  The analysis showed that the US, Italy, China, and the United Kingdom (UK) conducted the most research on COVID-19 vaccines, and the height of the countries' rectangles indicates that. Furthermore, most of the US studies have focused on COVID-19, COVID-19 Vaccination, COVID-19 Vaccines, Vaccine hesitancy, and COVID-19 Vaccines BNT162B2; these studies have been led by many researchers. Additionally, most Italia research has focused on topics, such as COVID-19, COVID-19 Vaccination, COVID-19 Vaccines, Vaccine hesitancy, COVID-19 Vaccines BNT162B2, and COVID-19 Pandemic; these studies have been conducted mostly by researchers such as AJ Pollard, T Lambe, L Kilmek, PK Aley, and M Voysey. However, Chinese and UK researchers, similarly to American researchers, focused on COVID-19, COVID-19 Vaccination, COVID-19 Vaccines, Vaccine hesitancy, and COVID-19 Vaccines BNT162B2. Figure 5 and Table 2 show the most active organizations in publishing studies on the COVID-19 vaccines. In total, more than 8000 institutions and universities around the world collaborated independently or in groups. Figure 5 indicates the institutions that cooperated at least in three documents together. This network consists of 1396 nodes and 13,428 links. The results presented in Table 2 and Figure 5 show that many of these studies are the result of collaboration between researchers from European, Asian, and American universities. As shown in Figure 5, the University of Oxford in the UK and the Harvard Medical School in the US, as the most active organizations, played a greater role than other institutions in publishing these studies, and this is visible in Figure 5 and Table 2. The analysis showed that the US, Italy, China, and the United Kingdom (UK) conducted the most research on COVID-19 vaccines, and the height of the countries' rectangles indicates that. Furthermore, most of the US studies have focused on COVID-19, COVID-19 Vaccination, COVID-19 Vaccines, Vaccine hesitancy, and COVID-19 Vaccines BNT162B2; these studies have been led by many researchers. Additionally, most Italia research has focused on topics, such as COVID-19, COVID-19 Vaccination, COVID-19 Vaccines, Vaccine hesitancy, COVID-19 Vaccines BNT162B2, and COVID-19 Pandemic; these studies have been conducted mostly by researchers such as AJ Pollard, T Lambe, L Kilmek, PK Aley, and M Voysey. However, Chinese and UK researchers, similarly to American researchers, focused on COVID-19, COVID-19 Vaccination, COVID-19 Vaccines, Vaccine hesitancy, and COVID-19 Vaccines BNT162B2. Figure 5 and Table 2 show the most active organizations in publishing studies on the COVID-19 vaccines. In total, more than 8000 institutions and universities around the world collaborated independently or in groups. Figure 5 indicates the institutions that cooperated at least in three documents together. This network consists of 1396 nodes and 13,428 links. The results presented in Table 2 and Figure 5 show that many of these studies are the result of collaboration between researchers from European, Asian, and American universities. As shown in Figure 5, the University of Oxford in the UK and the Harvard Medical School in the US, as the most active organizations, played a greater role than other institutions in publishing these studies, and this is visible in Figure 5 and Table 2.
Additionally, based on the results of Table 2, it can be argued that the US and the UK universities played a prominent role in publishing studies on the COVID-19 vaccines. Overall, from the 12 universities listed in Table 2, the US with 6, the UK with 4, and Canada and Israel with one university, were the most participating institutions in this field. However, Table 2 shows that the documents published by the University of Oxford and Emory University have had the greatest citation impact on the scientific community. It should be noted that the 151 studies published by researchers at the University of Oxford received 5546 citations, and the 76 studies published by researchers at the London School of Hygiene & Tropical Medicine obtained 4008 citations.  Additionally, based on the results of Table 2, it can be argued that the US and the UK universities played a prominent role in publishing studies on the COVID-19 vaccines. Overall, from the 12 universities listed in Table 2, the US with 6, the UK with 4, and Canada and Israel with one university, were the most participating institutions in this field. However, Table 2 shows that the documents published by the University of Oxford and Emory University have had the greatest citation impact on the scientific community. It should be noted that the 151 studies published by researchers at the University of Oxford received 5546 citations, and the 76 studies published by researchers at the London School of Hygiene & Tropical Medicine obtained 4008 citations.
To analyze the bibliographic information from documents on the COVID-19 vaccines, a three-field plot of institutions, keywords, and journals was designed, which allows us to identify institutions that have studied topics on the COVID-19 vaccines and provides the possibility to identify the field of journals that published such studies. As shown in Figure 6, institutions are on the left, keywords in the middle, and journals on the right. Figure 6 indicates the higher outputs of institutions, such as Oxford University,  To analyze the bibliographic information from documents on the COVID-19 vaccines, a three-field plot of institutions, keywords, and journals was designed, which allows us to identify institutions that have studied topics on the COVID-19 vaccines and provides the possibility to identify the field of journals that published such studies. As shown in Figure 6, institutions are on the left, keywords in the middle, and journals on the right. Figure 6 indicates the higher outputs of institutions, such as Oxford University, Harvard Medical Sciences, Tel Aviv University, National and Kapodistrian University of Athens, Johns Hopkins University, Stanford University, and Washington University, which are examined related fields to COVID-19, COVID-19 vaccination, COVID-19 vaccines, public health, COVID-19 vaccine acceptance, and COVID-19 vaccines bnt162b2. Generally, most of the research on vaccines at these institutions has been published in journals of Vaccines, Vaccine, Human Vaccines & Immunotherapeutics.

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Harvard Medical Sciences, Tel Aviv University, National and Kapodistrian University of Athens, Johns Hopkins University, Stanford University, and Washington University, which are examined related fields to COVID-19, COVID-19 vaccination, COVID-19 vaccines, public health, COVID-19 vaccine acceptance, and COVID-19 vaccines bnt162b2. Generally, most of the research on vaccines at these institutions has been published in journals of Vaccines, Vaccine, Human Vaccines & Immunotherapeutics.   Figure 7 indicate how the topic of study on the COVID-19 vaccines has been developed on five continents. Perhaps less of a topic addressed by all researchers worldwide, COVID-19 and the development of the vaccine have led to a global collaboration to eradicate it, and researchers in all countries are trying to achieve this by studying and investigating in this field. In Asia, China and India conducted the most research in this field. The US and Canada from the Americas and the UK and Italy from Europe published the highest number of articles on this topic. Australia from Oceania and South Africa from Africa also had the most studies on COVID-19 vaccines.   Figure 7 indicate how the topic of study on the COVID-19 vaccines has been developed on five continents. Perhaps less of a topic addressed by all researchers worldwide, COVID-19 and the development of the vaccine have led to a global collaboration to eradicate it, and researchers in all countries are trying to achieve this by studying and investigating in this field. In Asia, China and India conducted the most research in this field. The US and Canada from the Americas and the UK and Italy from Europe published the highest number of articles on this topic. Australia from Oceania and South Africa from Africa also had the most studies on COVID-19 vaccines.
In total, 122 countries contributed to the publication of studies on the COVID-19 vaccine, and the findings of the most active countries are presented in Table 3. Only four countries in the US, the UK, Italy, and China, with a publication of 61% of the total research conducted, were the most important and main countries producing publications on the COVID-19 vaccines, which played a prominent role in this field. The United States also had the greatest impact on the scientific community in this field by publishing 2104 studies and receiving 32,958 citations. Generally, the efforts of major pharmaceutical companies in the US, the UK, and China to study and investigate the production of the COVID-19 vaccine have been effective in increasing their publications in this field. In total, 122 countries contributed to the publication of studies on the COVID-19 vaccine, and the findings of the most active countries are presented in Table 3. Only four countries in the US, the UK, Italy, and China, with a publication of 61% of the total research conducted, were the most important and main countries producing publications on the COVID-19 vaccines, which played a prominent role in this field. The United States also had the greatest impact on the scientific community in this field by publishing 2104 studies and receiving 32,958 citations. Generally, the efforts of major pharmaceutical companies in the US, the UK, and China to study and investigate the production of the COVID-19 vaccine have been effective in increasing their publications in this field.

Rank
Countries NP  TC  1  US  2104  32,958  2  UK  776  15,269  3  Italy  521  3078  4  China  435  5671  5  Germany  391  9389  6  India  280  1836  7  Canada  263  2869  8  Australia  259  2003  9  France  247  1871  10  Israel  217  3000  11  Spain  205  1589  12 Switzerland 172 1702 Figure 8 shows the geographical distribution of countries participating in the research on the COVID-19 vaccine around the world. As can be seen in Figure 8 3  Italy  521  3078  4  China  435  5671  5  Germany  391  9389  6  India  280  1836  7  Canada  263  2869  8  Australia  259  2003  9  France  247  1871  10  Israel  217  3000  11  Spain  205  1589  12 Switzerland 172 1702 Figure 8 shows the geographical distribution of countries participating in the research on the COVID-19 vaccine around the world. As can be seen in Figure 8, the orange links indicate the wide range of collaborations that have taken place over the last three years since the beginning of the COVID-19 epidemic; authors from 153 countries have conducted studies related to the COVID-19 vaccine. Generally, most countries collaborated in publishing these studies so that the US-UK (192), the US-China (116), the US-Canada (95), and the US-Germany (86) have recorded the highest amount of scientific collaborations.
The results of Table 4 show that the Vaccines journal with 425 articles and the Vaccine journal with 185 articles had the highest number of publications in the field of COVID-19 vaccines. Studies published in the New England Journal of Medicine and the Lancet had the greatest citation impact on the scientific community, receiving 12,861 citations and 6776 citations, respectively, which could obtain significant citations in this field. The results of Table 4 also indicate that all 14 journals publishing research on the COVID-19 vaccines have an impact factor and are among the qualified journals in their field. According to the results of Table 4, the highest impact factor belongs to the New England Journal of Medicine with IF 91,245, and the lowest impact factor belongs to the International Journal of Environmental Research and Public Health with IF 3.39. Among them, 10 journals were Q1, 2 journals Q2 and Q3. Furthermore, Table 4 reveals that Nature Publishing Group and MDPI played the most role in this field with two journals. The results of Table 4 show that the Vaccines journal with 425 articles and the Vaccine journal with 185 articles had the highest number of publications in the field of COVID-19 vaccines. Studies published in the New England Journal of Medicine and the Lancet had the greatest citation impact on the scientific community, receiving 12,861 citations and 6776 citations, respectively, which could obtain significant citations in this field. The results of Table 4 also indicate that all 14 journals publishing research on the COVID-19 vaccines have an impact factor and are among the qualified journals in their field. According to the results of Table 4, the highest impact factor belongs to the New England Journal of Medicine with IF 91,245, and the lowest impact factor belongs to the International Journal of Environmental Research and Public Health with IF 3.39. Among them, 10 journals were Q1, 2 journals Q2 and Q3. Furthermore, Table 4 reveals that Nature Publishing Group and MDPI played the most role in this field with two journals.   Continuing to review the results of the publication of studies by journals, Figure 9 depicts the time trend of publication at the beginning of the COVID-19 epidemic in 2019 until now and informs us how to publish studies on the COVID-19 vaccines in journals. Figure 9 shows that since 2020, the trend for publishing studies in the Vaccines journal has been on an upward trend, which shows the special attention of this journal to the publication of studies on COVID vaccines. Overall, the journal has increased its number of studies from 13 in 2020 to 411 in 2021. It is followed by Vaccine and Human Vaccines & Immunotherapeutics, which were other research channels for researchers to publish studies on the COVID-19 vaccines in these years. These journals published 30 and 29 studies in 2020 and 155 and 145 studies in 2021, respectively. Continuing to review the results of the publication of studies by journals, Figure 9 depicts the time trend of publication at the beginning of the COVID-19 epidemic in 2019 until now and informs us how to publish studies on the COVID-19 vaccines in journals. Figure 9 shows that since 2020, the trend for publishing studies in the Vaccines journal has been on an upward trend, which shows the special attention of this journal to the publication of studies on COVID vaccines. Overall, the journal has increased its number of studies from 13 in 2020 to 411 in 2021. It is followed by Vaccine and Human Vaccines & Immunotherapeutics, which were other research channels for researchers to publish studies on the COVID-19 vaccines in these years. These journals published 30 and 29 studies in 2020 and 155 and 145 studies in 2021, respectively. According to the results presented in Table 5, the US Department of Health and Human Services with 437 studies and the National Institutes of Health NIH US with 408 studies had the highest support for the publication of scientific research on the COVID-19 vaccines. Note that the National Institutes of Health (NIH) is an affiliate of the US Department of Health and Human Services that plays a very important role in improving the national health of this country. Therefore, the presence of the National Institute of Allergy Infectious Diseases (NIAID) among the institutions supporting research on the COVID-19 vaccines is self-confirming. However, the European Commission and UK Research Innovation UKRI are in the next level with 169 and 143 studies, respectively. Given the extensive activities of these institutions and organizations, their outstanding efforts and support for research related to this field should not be overlooked because this support had a great impact on the production and manufacture of the COVID-19 vaccines. According to the results presented in Table 5, the US Department of Health and Human Services with 437 studies and the National Institutes of Health NIH US with 408 studies had the highest support for the publication of scientific research on the COVID-19 vaccines. Note that the National Institutes of Health (NIH) is an affiliate of the US Department of Health and Human Services that plays a very important role in improving the national health of this country. Therefore, the presence of the National Institute of Allergy Infectious Diseases (NIAID) among the institutions supporting research on the COVID-19 vaccines is self-confirming. However, the European Commission and UK Research Innovation UKRI are in the next level with 169 and 143 studies, respectively. Given the extensive activities of these institutions and organizations, their outstanding efforts and support for research related to this field should not be overlooked because this support had a great impact on the production and manufacture of the COVID-19 vaccines. The findings of Table 6 on the subject area of published studies on the COVID-19 vaccines reveal that more than 19% of this research are in the Immunology area, which could probably indicate that researchers in this field, in addition to treating and producing vaccines for this epidemic, also examined the types of immune responses to these vaccines. Furthermore, General & Internal Medicine with 1054 and Research Experimental Medicine with 834 studies were other active areas in this field. In total, researchers in these three areas played an influential role in the research outputs on the COVID-19 vaccines by publishing more than 49 percent of the studies. Additionally, the situation of other active and productive areas in this field is presented in Table 6. In other words, studies on the COVID-19 vaccines have not been ineffective in broadening the horizons of specialists, researchers, and physicians to control the disease.  Figure 10 illustrates the research focus of researchers in the field of COVID-19 vaccines based on the cloud label. Cloud tags show the extent to which researchers pay attention to topics; the higher the frequency of keywords used in research by researchers, the larger the tags, and the lower the frequency, the smaller the tags [22]. Figure 10 illustrates topics, such as COVID-19, COVID-19 vaccination, COVID-19 vaccines, vaccine hesitancy, COVID-19 pandemic, public health, COVID-19 vaccines bnt162b2, COVID-19 vaccine safety, healthcare workers, and vaccine acceptance. Figure 11 shows the trend of research on the COVID-19 vaccines based on the time zone view. In the linkage of Figure 11, the trend between nodes is moving from left to right, and in a way that indicates what topics the researchers have focused on and what topics they have tended to recently [23]. In addition, the time zone map represents the amount of attention of researchers to the topics in different time periods [23]. In 2019, topics, such as Spike protein, COVID-19, receptor binding domain, immunogenicity, safety of COVID-19 vaccines, infection, antibody, and neutralizing antibody are more visible in the researches of researchers in this period. The trend of research in 2020 confirms that in this period, researchers have reduced their research on the identification of this virus and focused their research on topics, such as spike, influenza COVID-19 vaccination, health, protection, COVID-19 vaccination, acute respiratory syndrome, respiratory syndrome COVID-19, immunization, influenza, immunity COVID-19 vaccines safety, disease, and behavior. However, the research trends of researchers in 2021 indicate that topics, such as COVID-19 infection, vaccine hesitancy COVID-19 vaccines, attitude, adult, and mortality have been more prominent than other topics in the studies of this period.  Figure 11 shows the trend of research on the COVID-19 vaccines based on the time zone view. In the linkage of Figure 11, the trend between nodes is moving from left to right, and in a way that indicates what topics the researchers have focused on and what topics they have tended to recently [23]. In addition, the time zone map represents the amount of attention of researchers to the topics in different time periods [23]. In 2019, topics, such as Spike protein, COVID-19, receptor binding domain, immunogenicity, safety of COVID-19 vaccines, infection, antibody, and neutralizing antibody are more visible in the researches of researchers in this period. The trend of research in 2020 confirms that in this period, researchers have reduced their research on the identification of this virus and focused their research on topics, such as spike, influenza COVID-19 vaccination, health, protection, COVID-19 vaccination, acute respiratory syndrome, respiratory syndrome COVID-19, immunization, influenza, immunity COVID-19 vaccines safety, disease, and behavior. However, the research trends of researchers in 2021 indicate that topics, such as COVID-19 infection, vaccine hesitancy COVID-19 vaccines, attitude, adult, and mortality have been more prominent than other topics in the studies of this period.    Figure 11 shows the trend of research on the COVID-19 vaccines based on the time zone view. In the linkage of Figure 11, the trend between nodes is moving from left to right, and in a way that indicates what topics the researchers have focused on and what topics they have tended to recently [23]. In addition, the time zone map represents the amount of attention of researchers to the topics in different time periods [23]. In 2019, topics, such as Spike protein, COVID-19, receptor binding domain, immunogenicity, safety of COVID-19 vaccines, infection, antibody, and neutralizing antibody are more visible in the researches of researchers in this period. The trend of research in 2020 confirms that in this period, researchers have reduced their research on the identification of this virus and focused their research on topics, such as spike, influenza COVID-19 vaccination, health, protection, COVID-19 vaccination, acute respiratory syndrome, respiratory syndrome COVID-19, immunization, influenza, immunity COVID-19 vaccines safety, disease, and behavior. However, the research trends of researchers in 2021 indicate that topics, such as COVID-19 infection, vaccine hesitancy COVID-19 vaccines, attitude, adult, and mortality have been more prominent than other topics in the studies of this period.   Figure 12, it can be argued that the US, as one of the leading countries in the COVID-19 vaccine, started its activity in the field of vaccine production in 2019, and its activities have continued with more intensity in recent years, which is seen from the red and yellow colors around the ring of the US. Additionally, the fact that this country is in the #1 cluster can confirm that the US has not only paid attention to the issue of vaccine production but has also pursued the issue of sociodemographic factor. period of the study of countries and institutions in the field of the COVID-19 vaccine on the horizontal axis and the research fields of their studies on the vertical axis are shown. Based on Figure 12, it can be argued that the US, as one of the leading countries in the COVID-19 vaccine, started its activity in the field of vaccine production in 2019, and its activities have continued with more intensity in recent years, which is seen from the red and yellow colors around the ring of the US. Additionally, the fact that this country is in the #1 cluster can confirm that the US has not only paid attention to the issue of vaccine production but has also pursued the issue of sociodemographic factor.   Based on Figure 12, it can be argued that the US, as one of the leading countries in the COVID-19 vaccine, started its activity in the field of vaccine production in 2019, and its activities have continued with more intensity in recent years, which is seen from the red and yellow colors around the ring of the US. Additionally, the fact that this country is in the #1 cluster can confirm that the US has not only paid attention to the issue of vaccine production but has also pursued the issue of sociodemographic factor.   England (the UK) and Germany, on the other hand, are other productive countries in this field, which is in the #1 cluster called the sociodemographic factor. China is also the source of the corona outbreak in cluster #2, and Italy and Russia in clusters #4 and #0 called the effective COVID-19 genomics and COVID-19 vaccines, are paying close attention to aspects of new strains and variants COVID-19 and COVID-19 vaccines. Figure 13 also consists of twelve clusters. In Figure 13, the University of Oxford, Harvard Medical School, London School of Hygiene & Tropical Medicine, Tel Aviv University, and Washington University formed the core of research institutes related to the COVID-19 vaccines in the clusters of public health, COVID-19 vaccines, COVID-19 vaccines hesitancy, and COVID-19 vaccination, which in itself can indicate that these institutions have conducted extensive work in these areas. However, in the link map, the Chinese Academy of Sciences, and the University of Texas Medical Branch had the highest citation flourishing scores, and in a way, the research conducted by researchers from these institutes have been able to attract the most attention of the scientific community. Table 7 shows that vaccines of AZD1222 (Oxford-AstraZeneca), BNT162b2 (Pfizer-BioNTech), Ad26.COV2.S (Johnson and Johnson), and mRNA-1273 (Moderna) have been injected by more countries. In total, these vaccines were licensed for use in 134, 132, 101, and 85 countries, respectively (See Appendix B). Additionally, the three BNT162b2, mRNA-1273, and AZD1222 vaccines with 940, 545, and 403 certificates, respectively, had the highest number of publications in the WoS database. It should be noted that according to the results of Table 7, China with 5, Russia and Iran each with 4, US with 3, and India with 2 vaccines, were the leading countries in vaccine production. Moreover, most of the values prepared are related to the two vaccines of BNT162b2 with 4,921,729,970 doses and mRNA-1273 with 3,078,314,353 doses.

Discussion
Due to the widespread prevalence of COVID-19 worldwide and its new mutations, many studies have been conducted by researchers on therapeutic and pharmacological methods to treat COVID-19 and to develop a vaccine to control the disease. According to the latest statistics approved by the World Health Organization, the number of patients with "COVID-19" disease in the world has reached 270,791,973 people, and the deaths of 5,318,216 people have been confirmed due to this disease. On 15 December 2021, more than 8,200,642,671 people worldwide had been vaccinated against the virus [9]. Therefore, the results indicate that by the end of 13 December 2021, 6288 studies related to the COVID-19 vaccines have been published in the Web of Science citation index.
The findings related to the trend of publications related to the COVID-19 vaccines indicate a significant increase compared to 2019 and 2020, meaning that more than 90 percent of these publications have been produced in 2021. Therefore, a reason for the significant increase in releasing research related to COVID-19 vaccines in 2021 may be the decline in global resilience faced with this epidemic and a more deadly strain of the virus, which prompted researchers to conduct further studies on the field of making and producing vaccines and finally controlling and eradicating this disease. Overall, the findings of researchers and institutions with the highest number of research publications showed that Pollard AJ and Lambe T of the University of Oxford had the highest number of publications on studies related to the COVID-19 vaccines. The findings from the most active research institutes also indicated that the University of Oxford in the UK and the Harvard Medical School in the US, as the most active institutions, played a more prominent role than other institutes in studies on the COVID-19 vaccines. The above results agree with the findings of Ay et al. [18].
The findings from leading countries in studies on the COVID-19 vaccines showed that researchers from the US published the most publications in this field; the results of Surulinathi et al. [24] and Ay et al. [18] confirm the findings of this study. The UK, Italy, and China also played a key role in the dissemination of the scientific documents. In other words, researchers from these four countries together played an important role in this field by publishing more than 61 percent of the research. The results of scientific collaboration between countries also showed that the highest level of scientific collaboration has been formed between researchers from the US-UK and the US-China. Note that countries that had the most scientific collaborations were countries that could publish most publications in this field.
The results of the journals that published research on the COVID-19 vaccines showed that the researchers published their scientific publications in 1321 journals. Among them, the Vaccines and Vaccine journals published the largest number of studies on the COVID-19 vaccines during the desired period. These journals are published by MDPI and Elsevier publications, respectively, and in terms of ranking of the Web of Science journals, they are ranked Q2 and Q3, respectively, and are in a good position in terms of impact factor. However, a review of support organizations for COVID-19 vaccine studies showed that the U.S. Department of Health & Human Services, with 437 studies, and the National Institutes of Health (NIH) from the US, with 408 studies, provided the most support from published studies on the COVID-19 vaccines. Additionally, the results related to the thematic fields of published studies showed that researchers in the field of Immunology with 1244 studies (19.8%), the field of General & Internal Medicine with 1054 studies (16.8%), and the field of Research Experimental Medicine with 834 studies (13.3%) percentage) had the most scientific publications in this field, which in the study Ay et al. [18], these three subject areas were also the leading thematic fields in studies on COVID-19 vaccines.
The state of research on the COVID-19 vaccines based on the time zone map showed that the initial studies in 2019 were more focused on identifying the COVID-19 virus and ways to combat it (COVID-19 vaccines efficacy, immunogenicity). However, the scientific research of researchers in 2020 has led to topics, such as COVID-19 and vaccines (COVID-19 vaccination, COVID-19 vaccines safety, and influenza COVID-19 vaccination), which indicates their serious attention to the development of vaccines to control and treat the disease. Finally, the research trend of studies in 2021 on topics, such as COVID-19 vaccines and their types and effects, vaccines hesitancy, the role of healthcare workers in COVID-19, as well as discussions on these vaccines on social media has been more than other studies.
Findings on the interconnected map of countries and research institutes showed that the US has paid serious attention to scientific activities about the production of COVID-19 vaccine, vaccination, and sociodemographic factor. The universities of Oxford, Harvard Medical School, Tel Aviv, Washington, and the London School of Hygiene & Tropical Medicine have also been major research institutes in the field of COVID-19 vaccines.

Conclusions
Generally, this study examined the trend of publications on the COVID-19 vaccines from the perspective of scientometric and depicted the topics and fields of study of countries, institutions, and researchers and the collaboration between them in this field. The findings of this study can be valuable through the identification and analysis of the most important actors (country, institution, researcher, and channel of release of COVID-19 vaccines), the research process and fields of study in the COVID-19 vaccine for researchers, countries, and policymakers in the fields of medical sciences and health to make better decisions and understand and ultimately progress in this field. There may also be more research in the future on other types of vaccines and comparing their effectiveness on mutated strains of the virus, vaccine acceptance, long-term side effects of these vaccines, COVID-19 vaccination from various perspectives, and other related topics due to the more prominent keywords, such as "COVID-19 vaccine" and "COVID-19 vaccination", which can also increase the upward trend of publication compared to recent years. Finally, there is a need to increase opportunities for financial support, more scientific collaborations, understanding and analyzing research of leading countries, and emulating them from different angles to make appropriate decisions.
Author Contributions: A.N., B.G., S.G., S.J., R.F., A.S. and A.A.S.: conceived and designed the study, collected the data, analysis and graphs, contributed to data analysis, interpretation and manuscript preparation, literature review, writing manuscript, and proofreading. All authors have read and agreed to the published version of the manuscript.
Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.