**4. Discussion**

By using LDA as the natural language processing approach, this study was able to capture the foci of COVID-19 related publications in different settings. This paper informed the rapid growth of research publications, and the global variation in research productivity and research interests. Moreover, findings of this study indicated that global scholars are paying attention to clinical management, viral pathogenesis, and public health responses, while other issues, such as psycho-social problems or impacts of COVID-19 on different vulnerable populations, are not-well investigated.

In this study, we found a greater number of publications regarding COVID-19 and SARS-CoV-2 in comparison with previous bibliometric studies [21–23]. For example, Lou et al. used the Medline database and only found 183 publications through February 29, 2020 [22]. This disparity could be justified that our search was far more comprehensive than these studies by using three major databases including the Medline, Scopus, and WOS. In addition, we included other document types such as letters, commentaries, or notes rather than concentrating only on original articles. As original papers require a long period for peer-review [30], scientists tended to publish their ideas in those document types first for receiving rapid feedbacks from others [31]. Therefore, we believed that our approach was appropriate given that these documents might partly reflect the research focus in each country.

The thematic maps of authors' keywords and terms reveal that major research themes included virological and molecular analysis of the virus; clinical, laboratory and radiology examinations; and global and public health responses. Our findings are in line with a previous bibliometric study, which showed that virology, clinical characteristics, and epidemiology of COVID-19 were found to be the major research foci with the highest volume of papers [22]. Indeed, it has been a short period of time since the onset of the pandemic, and these research areas are essential components for preventing and controlling the pandemic. Understanding the biology of SARS-CoV-2 is critical for the development of effective and safe screening tests, drugs, and vaccines, while investigations into clinical and paraclinical characteristics of COVID-19 could inform a fundamental method for appropriate patient management. Research on public health responses could illustrate the effectiveness of different policies and strategies to mitigate the consequences of the COVID-19 pandemic [32–34]. Notably, we believed that much research is ongoing as well as numerous papers are under reviewed, which will remarkably contribute to the global knowledge about COVID-19 in the short coming.

Results of topic modeling offer more penetrating insights into the emerging research themes. Of all identified topics, clinical aspects, particularly guidelines for emergency care and surgical management during the COVID-19 pandemic, were most frequent. Along with the rapid increase in the number of confirmed cases, the heavy demand for health facilities and health workers, along with the lack of effective treatment regimens, place a heavy burden and prevent the healthcare systems from operating efficiently. Without guidelines for prompt responses in emergency care, the burden caused by COVID-19 would go beyond the capacity of most health systems, especially for ICU care [35]. In addition, a number of SARS-CoV-2 infections emerged from operations were reported in China, suggesting the risk of virus exposure despite strict hygienic requirements and aseptic techniques during the surgical process [36]. Research for clinical guidelines, therefore, plays a critical role in mitigating the impact of COVID-19 on the healthcare system.

The origin and pathophysiology of the virus have attracted a great deal of attention since the beginning of the outbreak [37–39]. The interest in this topic has continued to rise as the virus has gone beyond China, where the first infection was reported, and positive cases have been found in most countries and territories [40]. On the other hand, the information that SARS-CoV-2 is a laboratory derived virus, albeit that this has been confirmed to be a false claim, gave rise to considerable controversy and also facilitated research on the nature of the virus [41]. Another topic that should be mentioned is national public health responses and actions against COVID-19, especially at the beginning of the pandemic when there was a wide difference in policies introduced by different governments. In particular, some countries advocated achieving herd immunity, whereas low- and middle-income countries (LMICs) implemented strict actions, including quarantine, isolation, social distancing, and community containment as soon as the outbreak occurred [42–45]. Although such measures have demonstrated their effectiveness, for optimal public health as well as economic outcomes, further investigations into their implementation within specific contextual factors should be prioritized [46]. Moreover, continued medical training for healthcare workers [47] and preventive measures for the workforce [48], along with frequent transparent communication and educational interventions for the public, is essential to strengthen the preventive capacity of each individual and thus, contribute to the global fight against COVID-19. Meanwhile, since COVID-19 has been reported to have no noticeable effect on pregnancy, research on COVID-19 among pregnant women received relatively slight interest [49].

Regarding the research foci in different country groups, it appeared that the share of publications regarding psychological health and related interventions was negatively associated with income level. This finding might imply that this topic might not be the priority of the countries, or in other words, developed nations show even less interest than the ones having lower-income [50]. However, COVID-19 caused a significant psychiatric impact [51], and this impact was maintained when the total number of COVID-19 cases continued to rise [52]. Developed nations are not immune from mental health issues and mental health services have often been disrupted during the COVID-19 pandemic [53]. Another reason which might play a role in this phenomenon is that most of the studies about this topic were cross-sectional surveys in the community, which were more affordable for low-income countries

to perform compared to other topics. Therefore, the share of publications in this topic in low-income countries might be higher than that in high-income countries.

In terms of treatment interventions, although all countries are making efforts to develop effective treatment regimens, high-income countries, with their vast financial resources, greater expertise, and infrastructure, demonstrated their bold attempt in this research area [54,55]. Meanwhile, compared to low-income nations, we observed a lower share of SARS-CoV-2 test-related publications among low-middle income countries, which might imply that these countries prioritized to other research fields such as treatment interventions given their resource-constraint [56]. In addition, while rapid transmission of COVID-19 has been triggering a strong need for the development of an effective vaccine, our results show minimal research on this topic. However, we do believe that the amount of research on vaccine development is possibly abundant according to the number of studies about COVID-19 vaccination registered in clinicaltrials.gov and the WHO Trial Registry Network. Because it requires remarkable amount of time to obtain results, the small amount of publications compared with other topics is understandable.

Findings also suggested that research on comorbidities associated with COVID-19 is relatively underdeveloped in countries with sporadic cases, in contrast with the extensive understanding and research on the effects of comorbidities on COVID-19 in those countries with a high number of infections [57,58]. On the other hand, the increase of transmission level was negatively correlated with the interest in treatment interventions. Although some high-income countries such as the United States, Canada, or the United Kingdom were classified as "community transmission" and greatly contributed to the progress of finding treatment interventions, most of the nations in this category were low-middle income countries (e.g., South American and African countries) and the governments tends to focus on preventive methods to prevent the pandemic from getting worse [2].

This study has several implications. To begin with, since there has been anecdotal evidence that promising drugs for COVID-19 such as Lopinavir/ritonavir (LPV/RTV), Chloroquine (CQ), and hydroxychloroquine (H0) have shown no significant benefits to health outcomes of patients, developing effective and safe medications specific for the treatment of COVID-19 is of utmost importance [59–61]. Furthermore, the findings show a lack of behavioral psychosocial research on how people react with COVID-19 emergency [32]. Future research should consider the risk factors of psychosocial distress at interpersonal or cultural aspect, impact of mass media and social media on behaviors of population to COVID-19, as well as behavior-change interventions to each research subject. Additionally, we found a lack of research on the social stigma caused by COVID-19. Due to the rapid contagion of the virus, fear and anxiety about being infected can give rise to stigma and discrimination toward people, places, or things. For instance, people associated with the disease, such as being in a neighborhood of high risk or being a civilian of a nation with a high rate of COVID-19 infection, are often stigmatized [62,63]. Stigma can also arise when people are released from quarantine, even though they have been confirmed to be negative and are no longer risk. Although there have been several published guidelines for reducing social stigma related to COVID-19, further investigations into the detrimental effects of social stigma and development of interventions for this problem should be considered [62,63]. Finally, due to the rapid spread of this disease, the vulnerable population, such as the elderly living in nursing homes, workers in industrial zones, refugees, migrants, or persons with disabilities are at higher risk of getting an infection, will need extra precautions [64]. However, these high-risk clusters have not received enough concern from the researchers, even on commentary or local government. More research and preventive actions should be done so as to not leave these people behind [64].

To our knowledge, this is the first analysis using text mining and text modeling to investigate the research foci of the worldwide COVID-19 publications. However, some limitations should be noted. The restriction of the search strategy to the English language might not reflect globalized practices and the research priority of a country. Analyses of keywords, titles, and abstracts may not fully reflect the content of articles. However, with the combination of three large datasets and various techniques of text mining, this study is useful for an overview of the research direction. Moreover, our correlation

analysis was based on population data, which might not reflect the causes of the research tendency in each country. Since the publications on COVID-19 will rapidly grow in the coming time, further studies should be performed with more advanced techniques to elucidate our findings.
