1. Introduction
Since COVID-19 is still spreading worldwide, it has become a public health priority [1, 2]. As of November 18, 2021, more than 255767656 cases and more than 5139781 deaths, and only 231171572 recovered cases of COVID-19 had been reported globally. The United States, India, and Brazil had the highest number of cases globally, with 48287925, 34478517, and 21977661 total cases, respectively. These countries had the worst hits in all aspects of the economy, medical, etc., from COVID-19 [3, 4, 5, 6, 7, 8, 9]. One of the differences among countries in terms of death and recovery rates of COVID-19 may be related to social factors that affect the adherence to health principles, such as physical distancing, wearing a mask, and washing hands frequently, which cause long-term disruptions in travel, work, as well as social and cultural activities. However, economic, legal, technological, geographical, and cultural barriers can limit the government’s ability to effectively respond to crucial public health needs [1, 10, 11]. Putnam conceptualizes social capital as the behavior of networks and social relationships characterized by trust and reciprocal action [11, 12, 13]. Social capital considerations appear as a powerful reference for understanding how to improve the implementation of health interventions to effectively expand the health services for the entire community [10, 14, 15]. The definition of social capital in the context of epidemics is the social resources that have risen from networks of persistent social relationships under conditions of physical isolation, such as the COVID-19 epidemic [16, 17, 18]. Social capital has three dimensions: networks which are the individual’s social relationships and interactions, which are considered essential components of social capital; the cooperation norm, which is the social capital criteria; and trust, which is an essential element for strengthening cooperation due to the predictability of behavior of others and includes personal and generalized trust [19, 20]. In public health, many researchers have studied social capital as a variable to improve health outcomes and a framework to evaluate public health interventions [21, 22, 23]. Aspects of social capital are evident in the community’s efforts in the early phases of the epidemic and can complete the government’s efforts.
Various studies have shown that social capital affects the characteristics of infectious diseases, such as death rate, recovery rate, new cases, and the number of diagnostic tests, just like the relative income inequality which forms a social pattern in the distribution of infectious diseases in societies [1, 24, 25]. Elgar et al. suggested that societies that are economically more unequal and lack sufficient capacity in some dimensions of social capital experienced more deaths from COVID-19. These findings indicate much newer cases and fewer recovery cases due to COVID-19. In addition, social trust and group affiliations were associated with higher mortality due to COVID-19, probably due to behavioral contagion and inconsistency with the physical distance policy [1, 21]. Social capital is a crucial determinant of health. For example, the states with lower levels of group social capital have more deaths from COVID-19 than states with higher levels of social capital. New studies have shown COVID-19 patterns with more transmission of infection and worse health consequences due to working conditions and overcrowded housing [26, 27]. Some research in the United States has shown mild correlations between state-level income inequality and COVID-19 cases, deaths, and other communicable diseases, such as sexually-transmitted diseases and tuberculosis [28, 29]. Social capital has received more attention in recent decades, particularly in collaboration and innovation research. Research has also recently begun to view social capital as a potential protector against the problems caused by COVID-19. By investigating income inequality, social bounds, and links that facilitate collective action, we can understand why some countries have experienced fewer COVID-19 deaths and more recovery than others. However, the benefits of social capital for surviving an epidemic have not yet been explored [1, 10]. Therefore, the present study was conducted to investigate the correlation between social capital and epidemiological indices of coronavirus disease, including the cumulative incidence rate of cases, the cumulative incidence rate of death, performed COVID-19 tests per million, the recovery rate, and the case fatality rate.
2. Methods 
The present study investigated the relationship between COVID-19 indices, such as the cumulative incidence rate of cases, the cumulative incidence rate of death, the number of diagnostic tests per million, and the recovery rate with social capital. We collected the data on COVID-19 indices available on the Worldometer website (https://www.worldometers.info/) for the period from the first COVID-19 report to November 30, 2020. Also, the details about COVID-19 indices and the data collected on COVID-19 indices have been previously published [30].
Data availability was as follows, social capital data for 165 countries, the cumulative incidence rate of cases for 165 countries, the cumulative incidence rate of death for 157 countries, the number of diagnostic tests per million for 153 countries, the recovery rate for 159 countries, and the case fatality rate for 157 countries. Social capital data were available on the www.solability.com website in 2019 [31]. Social capital was defined as follows: Social capital is naturally occurring social relationships among persons which promote or assist the acquisition of skills and traits valued in the marketplace. Social capital is also an asset that may be as significant as financial capital in accounting for the maintenance of inequality in our society [32]. 
Statistical analysis
Scatter plot of social capital was drawn in terms of COVID-19 indices of the cumulative incidence rate of cases, the cumulative incidence rate of death, the number of diagnostic tests performed per million, the recovery rate, and the case fatality rate for all studied countries. The Spearman correlation coefficient was used to determine the correlation between social capital and COVID-19 indices.
3. Results
The study showed that among the studied countries, the highest cumulative incidence rate of COVID-19 cases was in Montenegro (60310.56 per million) and Luxembourg (54807.89 per million), while the lowest cumulative incidence rate of cases was in Tanzania (8.42 per million) and in Samoa (10.05 per million). The highest cumulative incidence rates of death due to COVID-19 were in Belgium (1425.15 per million) and Spain (1118.96 per million), while the lowest cumulative incidence rates of death were in Burundi (0.08 per million) and Tanzania (0.35 per million). The highest COVID-19 diagnostic tests performed per million were in Luxembourg (2180641.18 per million) and the United Arab Emirates (1682880.81 per million). In contrast, the lowest diagnostic tests per million were reported from Yemen (560.05 per million) and Niger (1885.52 per million). The highest recovery rates of COVID-19 were in Timor-Leste (100%) and Singapore (99.86%), and the lowest rates were in Belgium (6.48%) and France (7.28%). The highest case fatality rates of COVID-19 were in Yemen (28.34%) and Mexico (9.54%) and the lowest rates were in Singapore (0.05%) and Burundi (0.15%). Also, the highest social capital was in Finland (58.78%), and the lowest was in the Bahamas (23.91%).
Table 1 presents the correlation coefficient between COVID-19 indices and social capital.


The present study shows that social capital has a significant direct correlation with the cumulative incidence rate of cases, the cumulative incidence rate of death, and the number of performed COVID-19 diagnostic tests per million (P<0.001), meaning that increasing social capital, the cumulative incidence rate of cases, the cumulative incidence rate of death and the number of performed COVID-19 diagnostic tests per million also increased. Social capital was inversely correlated with recovery and mortality rates, case fatality (P=0.007), and recovery rates (P=0.008). In countries with populations of ≥10 million, a significant direct relationship was observed between social capital and the cumulative incidence rate of the cases, the cumulative incidence rate of death, and the number of performed COVID-19 diagnostic tests per million (P<0.001). Social capital was inversely correlated with the recovery rate (P=0.03) but not the case fatality rate (P=0.11). 
Figure 1 shows the scatter plot of the social capital index by cumulative incidence rate of cases, the cumulative incidence rate of death, the number of performed diagnostic tests per million, recovery rate, and case fatality rate in all countries and countries with populations of ≥10 million.

In all countries, the highest R2 was observed in case fatality rate (CFR) and the number of performed COVID-19 diagnostic tests per million (R2=0.221). In countries with a population of ≥10 million, the highest R2 was observed in the number of performed COVID-19 diagnostic tests per million (R2=0.247) and the cumulative incidence rate of cases (R2=0.191). 
Figure 2 illustrates the box plot of the social capital index and COVID-19 indices.

The horizontal line within the box represents the median. The box and error bars indicate the interquartile range and range, respectively.
4. Discussion
Consistent with Elgar et al. study, our study showed an inverse correlation between social capital and case fatality rate because, with the expansion of the social network, which is a subset of social capital, a person trusts others more and, as a result, has a greater desire to communicate with them. Also, at older ages, the desire of people to participate more in social activities and adherence to physical distancing, which is one of the preventive factors of COVID-19, decreases among them. These factors will lead to an increase in the number of patients and death. Therefore, the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) state that people 65 years and older are more likely to get COVID-19 due to chronic diseases. Therefore, they recommended that these people be vaccinated first. They concluded that adults 65 and older who received both doses of either Pfizer-BioNTech or Moderna COVID-19 vaccines showed a 94% reduced risk of COVID-19-related hospitalization. An evaluation was conducted at 24 hospitals in 14 states under real-world conditions, January-March 2021 [1, 33, 34, 35]. Another study suggests that countries with higher social capital had lower mortality and recovery rates for COVID-19, which is consistent with the present study. This result may be because countries with high social capital performed more COVID-19 diagnostic tests, which led to greater identification of patients with COVID-19 and reduced mortality [14]. Cary Wu et al. reported that countries with higher social capital were better able to respond to the pandemics. Thus, countries with higher social capital had higher cumulative incidence rates of cases and cumulative incidence rates of death. Also, high social capital in these countries has led to an increase in the number of diagnostic tests performed for COVID-19 and positive tests; therefore, increasing social capital can affect all these factors, which is similar to the findings of the present study. WHO argues that polymerase chain reaction (PCR) testing is more accurate than rapid antigen testing, but in the case of the COVID-19 pandemic, these tests will also be valuable and useful. Therefore, it can be said that countries with higher social capital use PCR tests more, and countries with less social capital use rapid antigen tests. This will lead to accurate and rapid diagnoses of COVID-19 disease in countries with high social capital [36, 37, 38]. A study on the impact of social capital on individual responses to COVID-19 presented that social networks in countries with large populations and higher social capital harmed adherence to physical distancing, which led to an increased number of diagnostic tests and positive tests; as a result, these factors would also have an undesirable effect on the cumulative incidence rates of cases and deaths [18, 39, 40, 41]. One of the possible reasons for the relationship between social support and the cumulative incidence rate of fatalities can be that with the increase in social support, the number of people for corona diagnostic tests has increased. As a result, the number of positive cases has increased, further increasing the number of deaths. This result needs to be further investigated using analytical studies. Studies similar to ours showed that social capital had many advantages during a crisis and pandemic scenario. Societies with high social capital responded to pandemics more efficiently than societies with low social capital. The mortality rate was lower in societies with high social capital; therefore, increasing social capital indicators is emphasized. Social capital is associated with more diagnostic tests performed in these communities but is inversely related to the recovery rate [42, 43, 44]. Other studies consistent with the present study exhibited that social capital and community health indices were negatively correlated with COVID-19 growth rate at both state and country levels, and increasing social capital was related to the slower spread of COVID-19 infection and more adherence to physical distancing protocols resulting to decreased case fatality rate [45, 46]. 
5. Conclusion
Considering that social capital has a statistically significant relationship with the indices of case fatality rate, recovery rate, cumulative incidence rate of cases and death, it is possible to increase social capital with appropriate interventions by relevant individuals and organizations to improve the pandemic management in different countries.
Strength and limitation
The strength of the present study is that the relationship between social capital and COVID-19 indices was examined in 165 countries for the first time. But the limitation of this study is the use of ecological data and the possibility of ecological fallacy. Another study limitation was the lack of information on social capital in some countries.

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Research Ethics Committee of Shiraz University of Medical Sciences (Code: IR.SUMS.REC.1399.174).

Funding
This study was approved and financially supported by Shiraz University of Medical Sciences (Grant No.: 99-01-106-19536). The study sponsors had no role in the study design, in the collection, analysis, and interpretation of data, in the report’s writing, and in the decision to submit the paper for publication.

Authors' contributions
Designing the study: Alireza Mirahmadizadeh and Mousa Ghelichi-Ghojogh; Data collection: Kimia Jokari; Writing the manuscript: Alireza Jafari and Fatemeh Rezaei ; Revising the manuscript: Zahra Maleki and Roya Sahebi; Helping with statistical analysis and preparing the illustrations: Jafar Hassanzadeh and Fatemeh Rezaei; Editing the manuscript: Ali Akbari and Mehrzad Lotfi; Study conception and design, Approval of the final manuscript: All authors.

Conflict of interest
The authors declared no conflict of interest.

Acknowledgments
The authors thank the vice chancellor for research and technology of Shiraz University of Medical Sciences for their financial support.


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