Which are factors determining a low COVID-19 mortality in society? High health expenditure and lower exposure of population to air pollution as critical factors for an effective strategy to cope with future pandemics similar to COVID-19

One of the problems hardly claried in the scientic eld of Coronavirus Disease 2019 (COVID-19) is inter-related factors associated with a lower mortality of COVID-19 to design effective strategies to cope with unforeseen pandemic crises. The main goal of this study is to explain these factors determining a lower fatality rate of the Coronavirus disease 2019 (COVID-19) in society with a global analysis based on more than 160 countries worldwide. This study reveals a novel nding: countries with a low average COVID-19 mortality have high investments in health sectors as % of GDP (>7.5%), high health expenditures per capita (>$2,300) associated with a lower exposure of population to days exceeding safe levels of particulate matter (PM 2.5 ), reinforcing these factors with a policy response of lockdown. In addition, these countries have lower fatality rates of COVID-19, regardless a higher percentage of population aged more than 65 years in these countries. Overall, then, this study must conclude that an effective strategy to reduce the negative impact of future epidemics similar to COVID-19 has to be based on a reinforcement of healthcare sector to have an ecient organization prearranged to cope with pandemics of new viral agents and to be able to minimize fatality rates in a context of sustainable environment having low air pollution.

argue that health policy and involvement of nurse leaders have a main role to mitigate COVID-19 pandemic. Kapitsinis (2020) investigates the diffusion of the novel coronavirus in nine European countries and pinpoints that health investments play a vital role to alleviate mortality rate of COVID-19. Ahmed et al. (2020) focus on different demographic, socioeconomic, and lifestyle health factors in countries to explain the variety of COVID-19 effects in society. This study by Ahmed et al. (2020) suggests that health expenditure per capita has a positive relation with case recovery; in particular, countries having high healthcare investments associated with high average age and proportion of urban population have high number of case fatality; as a consequence, investment in health sector is one of the factors that plays a vital role to control the spread of COVID-19 pandemic. Barrera-Algarín et al. (2020) state that in Europe lower investment in health per capita is associated with high numbers of COVID-19 deaths per million inhabitants; in general, a high negative impact of COVID-19 in terms of mortality is due to low expenditure in public health associated with high socioeconomic inequality. In this research eld, Kavitha and Madhavaprasad (2020) underline the main role of preventive health care measures and social distancing applied on a vast portion of population to constraint the spread of COVID-19. Iyanda et al. (2020) argue that developing public health and epidemiological surveillance programs for the outbreak can both reduce COVID-19 and prevent unnecessary deaths. Gaffney et al. (2020, p. 396) maintain that: "the United States' underfunded public health infrastructure, fragmented medical care system, and inadequate social protections impose particular impediments to mitigating and managing the outbreak. . .. While the United States has a relatively generous supply of Intensive Care Unit beds and most other health care infrastructure, such medical resources are often unevenly distributed or deployed, leaving some areas illprepared for a severe respiratory epidemic". Moreover, González-Bustamante (2021) shows in South America that pressure on the health system affects interventions of government and strong economic lobbies of countries can delay appropriate policies of containment. Jin and Qian (2020) measure: "the Chinese publichealth expenditure at national and provincial levels …, and then compare it with the expenditures of other countries. The results show that: (1) the level of public-health expenditure in China is relatively low and far lower than that in developed countries; (2) Chinese governments have not paid enough attention to the prevention and control of major public-health emergencies, which may be an important reason for the outbreak of COVID-19; (3) Chinese public-health expenditure shows a uctuating growth trend, but the growth rate is so slow that it is lower than that of GDP and scal expenditure; (4) although the Chinese government inclines the public-health expenditure to the poor provinces in central and western regions, the imbalance and inequity of public-health resource allocation are still expanding among provinces; (5) there is a lot of waste of resources in the publichealth system, which seriously reduces the e ciency of public-health expenditure in China. Therefore, the Chinese government should improve the quantity and quality of public-health expenditure in the above aspects". Siddiqui et al. (2020) analyze India in the presence of COVID-19 pandemic and show that: "low public health expenditure combined with a lack of infrastructure and low scal response implies several challenges to scale up the COVID-19 response and management. Therefore, an emergency preparedness and response plan is essential to integrate into the health system of India".
Overall, the, the vast literature shows different results but what is hardly known is to explain manifold factors determining a lower mortality in society to design an effective strategy to constrain future epidemics similar to COVID-19. This investigation is part of a large research project on factors determining the transmission dynamics of the COVID-19 pandemic and socioeconomic impact of public policies to cope with COVID-19 pandemic crisis. Results of the study here can clarify factors to reduce mortality rates of infectious diseases to design effective strategies to constrain future epidemics similar to COVID-19.

Materials And Methods
This study has the primary objective to explain factors determining a lower fatality rate of the COVID-19 in countries. The study is based on a sample of 161 countries worldwide that is categorized in two sub-samples according to the level of Gross Domestic Product per capita (wealth of individuals) to have a comparable institutional and socioeconomic framework of investigation between countries.

Research setting and measures
Sample, N=161 countries worldwide.
The measures under study are: Number of COVID-19 infected individuals is measured with con rmed cases (%) of COVID-19 divided by population of countries under study on 14 December 2020. Source of data: Johns Hopkins Center for System Science and Engineering (2020).
Number of COVID-19 deaths is measured with fatality rate (%) of COVID-19 given by deaths divided by total infected individuals in countries on 14 December 2020. Source of data: Johns Hopkins Center for System Science and Engineering (2020).
Wealth of population is measured with Gross Domestic Product (GDP) per capita, Purchasing Power Parity, PPP (current international $) in 2019 (last year available in dataset). GDP per capita is gross domestic product divided by midyear population. GDP is the sum of gross value added by all resident producers in the economy plus any product taxes and minus any subsidies not included in the value of products. It is calculated without making deductions for depreciation of fabricated assets or for depletion and degradation of natural resources. Data are in current U.S. dollars. Source of data: World Bank (2020).
The structure of health sector is measured: a) current health expenditure (% of GDP) in 2017: Level of current health expenditure expressed as a percentage of GDP. Estimates of current health expenditures include healthcare goods and services consumed during each year. This indicator does not include capital health expenditures such as buildings, machinery, IT and stocks of vaccines for emergency or outbreaks. Source of data: World Bank (2020a); b) Domestic general government health expenditure per capita, PPP (current international $) in 2017 (last year available): Public expenditure on health from domestic sources per capita expressed in international dollars at purchasing power parity (PPP time series based on ICP2011 PPP). Source: World Bank (2020b).
Elderly is measured with population aged 65 and above as a percentage of the total population: Population is based on the de facto de nition of population, which counts all residents regardless of legal status or citizenship in 2019 (last year available). Source: World Bank (2020c). Population aged 65 and above is an important factor because many studies argue negative effects of COVID-19 on older population (Cohen-Mans eld, 2020).
Air pollution is measured by PM 2.5 air pollution, population exposed to levels exceeding WHO guideline value (% of total) in 2017 (last year available): Percent of population exposed to ambient concentrations of PM 2.5 that exceed the WHO guideline value is de ned as the portion of a country's population living in places where mean annual concentrations of PM 2.5 are greater than 10 micrograms per cubic meter, the guideline value recommended by the World Health Organization as the lower end of the range of concentrations over which adverse health effects due to PM 2.5 exposure have been observed. Source: World Bank (2020d). Studies reveal that areas with frequently high levels of air pollution -exceeding safe levels of ozone or particulate matter -had higher numbers of COVID-19 related infected individuals and deaths (Coccia, , 2020a(Coccia, , 2020b(Coccia, , 2020c(Coccia, , 2020dCoccia, 2021;Martelletti and Martelletti, 2020). Moreover, high concentrations of nitrogen dioxide and particulate air pollutant induce serious damages to the immune system of people, weakening it to cope with infectious diseases of viral agents (Glencross et al., 2020) Containment measure of COVID-19 lockdown is measured with total days of lockdown across countries over 2020-2021 period (until January 2021). Tobías (2020, p. 2) states that: "Lockdown, including restricted social contact and keeping open only those businesses essential to the country's supply chains, has had a bene cial effect". Flaxman et al. (2020) show that lockdowns seem to have effectively reduced transmission of the COVID-19. Atalan (2020) argues that countries can start the policy response of lockdown when there is an acceleration of daily con rmed cases beyond a critical threshold and can end it when there is a strong reduction of Intensive Care Unit (ICU) admissions (cf., Chaudhry et al., 2020). Source: COVID-19 pandemic lockdowns (2020).

Data analysis procedure
The sample of N=161 countries is divided in two sub-samples (group 1 and 2) as follows: Countries with a Gross Domestic Product per capita higher than arithmetic mean of the sample (group 1) Countries with a Gross Domestic Product per capita lower and/or equal than arithmetic mean of the sample (group 2) Firstly, data are analyzed with descriptive statistics by arithmetic mean (M) and standard deviation (SD), using a comparative approach between two groups of countries just mentioned. In addition, to check the normality of distribution and apply correctly parametric analysis the skewness and kurtosis coe cients are computed and in the presence of not normal distributions, variables are transformed in logarithmic scale.
Secondly, to assess whether the difference of arithmetic mean of variables between group 1 and 2 is signi cant, the Independent Samples t-Test is performed. In particular, the Independent Samples t-Test compares the means of two independent groups in order to determine whether there is statistical evidence that the associated population means are signi cantly different. The Independent Samples t Test requires the assumption of homogeneity of variance --i.e., both groups have the same variance and as a consequence Levene's Test is performed. The hypotheses for Levene's test are: H 0 : σ 1 2 -σ 2 2 = 0 (the population variances of group 1 and 2 are equal) H 1 : σ 1 2 -σ 2 2 ≠ 0 ("he population variances of group 1 and 2 are not equal) This implies that if we reject the null hypothesis of Levene's Test, it suggests that the variances of the two groups are not equal; i.e., that the homogeneity of variances assumption is violated. If Levene's test indicates that the variances are equal across the two groups (i.e., p-value large), Equal variances assumed. If Levene's test indicates that the variances are not equal across the two groups (i.e., p-value small), the assumption is: Equal variances not assumed. After that, null hypothesis (H 0 ) and alternative hypothesis (H 1 ) of the Independent Samples t-Test are: H 0 : µ 1 = µ 2 , the two population means are equal in countries with a higher and lower GDP per capita H 1 : µ 1 ≠ µ 2 , the two population means are not equal in countries having a higher and lower GDP per capita Statistical analyses are performed with the Statistics Software SPSSâ version 26.

Results
The arithmetic mean ( Table 1 shows that fatality rate is lower (1.68%) in richer countries that have an average GDP per capita of more than $46,000 per capita, a higher health expenditure (% of GDP) of roughly 7.6%, higher government health expenditure per capita of about $2,300, a lower exposure of population to levels exceeding PM 2.5 air pollution according to WHO guidelines and longer period of lockdown, regardless a higher percentage of population aged more than 65 years and higher incidence of con rmed cases on population in these countries (cf., Figure 1 and Table 2). In order to assess the signi cance of the difference of arithmetic mean between groups of countries under study (table 2), the Independent Samples t Test is performed. The p-value of Levene's test is signi cant, and we have to reject the null of Levene's test and conclude that the variance in the groups under study is signi cantly different (i.e., Equal variances not assumed), except COVID-19 pandemic lockdown that has p-value<.06 and Equal variances assumed. There was a signi cant difference in mean general government health expenditure per capita between countries with GDP Lower than $22,794 and GDP Higher than $22,794 (t 59.48 = -11.41, p < .001).
There was a signi cant difference in mean population aged 65 and above as a percentage of total population between countries with GDP Lower than $22,794 and GDP Higher than $22,794 (t 81.80 = -9.98, p < .001).
There was a signi cant difference in mean PM 2.5 air pollution, population exposed to levels exceeding WHO guideline value (% of total) between countries with GDP Lower than $22,794 and GDP Higher than $22,794 (t 52.34 = 3.19, p < .01).
Hence, ndings suggest that fatality rate in richer countries (1.7%) is lower than medium-low income per capita countries (2.3%). Factors determining the mitigation of the fatality of COVID-19 in society can be due to a higher health expenditure (% of GDP) of roughly 7.6%, higher government health expenditure per capita of about $2,300, a lower exposure of population to levels exceeding PM 2.5 air pollution according to WHO guidelines and longer lockdown, though these countries have a higher percentage of population aged more than 65 years and higher incidence of con rmed cases on population.
These analyses provide important, very important results to constrain the effects of COVID-19 pandemic and future epidemics similar to COVID-19; in particular, an effective strategy has to be based on health policy with higher healthcare expenditure as percentage of GDP, environmental policies based on reduction of exposure of population to air pollution and nally a timely policy response based on lockdown of a long duration, in a context of general development of nations ).

Discussion, Policy Implications And Concluding Observations
One of the problems in the presence of COVID-19 pandemic crisis is to mitigate the mortality in society.
Previous studies suggest that measures of containment can constraint the human-to-human transmission dynamics of infectious diseases and negative effects in society (Atalan, 2020;Prem et al., 2020;Tobías, 2020). However, what this study adds to current studies on the COVID-19 global pandemic crisis is that a comprehensive strategy to reduce fatality rates of COVID-19 in society is associated with critical factors as schematically summarized in the gure 2.
The main aspects to mitigate fatality rates are focused on appropriate previous health and environmental policies and current policy responses to cope with COVID-19 pandemic crisis. In particular,

Health Policy
This study reveals that countries with a lower fatality rates have a high health expenditure (% of GDP) of roughly 7.6% and government health expenditure per capita of about $2,300, whereas countries with a higher fatality rates have a health expenditure (% of GDP) of roughly 6% and government health expenditure per capita of about $243 that indicate a weak healthcare sector to cope with pandemics and also other diseases. This main result is con rmed by other scholars, such as Kapitsinis (2020) that argues how health investments over time are a critical health policy to mitigate mortality rate of COVID-19.

Environmental policy
This study shows that environment plays a vital role for impact of COVID-19 in society; in particular, a low rate of fatality is associated with a low impact of air pollution on population: considering PM 2.5 air pollution, population exposed to levels exceeding WHO guideline value (% of total) is 72% in countries with a lower fatality rate, whereas in countries with a higher incidence of mortality of COVID-19 is almost 98%! Coccia ( , 2020aCoccia ( , 2020bCoccia ( , 2020c nds out that number of infected people was higher in Italian cities with >100 days per year exceeding limits set for PM 10 or ozone, cities located in hinterland zones (i.e. away from the coast), cities having a low average wind speed and cities with a lower temperature. In fact, diffusion of the COVID-19 is higher in cities with low wind speed that prevents the dispersion of air pollutants and bio aerosols that can include bacteria and viruses, such as SARS-CoV-2 . Guo et al. (2019) argue that in recent years, haze pollution is a serious environmental problem affecting cities, proposing policies for urban planning that improve respiratory health of population. In fact, improvements in air quality have been accompanied by demonstrable bene ts to human health. In this perspective, countries should introduce organizational, product and process innovations directed to a sustainable economic development and sustainable technologies for the improvement of environment, atmosphere, air quality and especially public health to cope with epidemics similar to COVID-19. In this context, countries should also support the expansion of hospital capacity and testing capabilities to reduce diagnostic delays, the application of arti cial intelligence and new ICT technologies for improving diagnostics, the development of effective vaccines, antivirals and other innovative drugs that can counteract future global public health threat in the presence of new epidemics similar to COVID-19, etc. (Coccia, 2005(Coccia, , 2017(Coccia, , 2017a(Coccia, , 2017b(Coccia, , 2019a(Coccia, , 2019bCoccia, 2020e;Coccia and Watts, 2020).

Policy responses based on containment measure of lockdown
This study also shows that mortality of COVID-19 is lower in the presence of longer lockdowns. The model by Balmford et al. (2020) reveals that countries with an immediate application of lockdown reduced deaths compared to countries that delayed the application of this strong containment measure. Gatto et al. (2020) maintain that restriction to mobility and human interactions can reduce transmission dynamics of the COVID-19 by about 45%. Janssen and van der Voort (2020) show the utility of "smart lockdown" as policy responses based on suggested and not mandated mitigation measures focused on responsibility of individuals in the presence of speci c local conditions. In this context, new studies show that speci c places have a high risk to be COVID-19 outbreaks (e.g., restaurants, gyms, stadium, discotheques, etc.), generating a lot of infections (Chang et al., 2020); as a consequence, selected measures of containment, such as restricting maximum occupancy of these speci c places, are more effective interventions than policies based on uniformly reducing mobility of people (Chang et al., 2020;cf., Renardy et al., 2020).

Policy and theoretical implications
Overall, then, one of the most important ndings here is that an appropriate health policy that supports healthcare sector, a sustainable environmental policy that reduces the exposure of population to air pollution and a timely policy response of lockdown can induce a reduction of COVID-19 fatality rates, regardless a higher incidence of con rmed cases and a higher percentage of elderly on total population in countries. In general, the COVID-19 pandemic crisis needs high investments in health sector, sustainable policies and policy responses based on agility and adaptive governance. Evans and Bahrami (2020) pinpoint that super-exibility can be an appropriate approach to cope with environmental threats of current COVID-19 in which decision making should be oriented to versatility, agility, and resilience. In short, to reiterate, this study suggests that in order to constrain the impact in society of new pandemic waves of COVID-19 and future epidemics similar to the COVID-19, regions and nations have to apply critical policies directed to increase investments in healthcare sectors and reduce the sources of air pollution to improve air quality Coccia, 2020f, 2020g).

Limitations and concluding observations
This statistical analysis here suggests mainly association between the variables under study because of manifold confounding factors that in uence variables (Sabat et al., 2020, p. 917). The positive side of this study is a large dataset for a global analysis of countries that have been categorized in two sub-samples to have homogenous groups to perform a comparative analysis. However, future studies have to reinforce the generalization of these main ndings with additional statistical analyses over time and space. To conclude, an effective strategy to reduce the negative impact of future epidemics similar to COVID-19 has to be based on preventive high investments in healthcare sector to have a prearranged e cient organization, in a sustainable environment, to cope with pandemics of new viral agents to be able to minimize fatality rates of new waves of COVID-19 pandemic and similar viral agents in future.

Declarations
Declaration of competing interest. The author declares that he has no known competing nancial interests or personal relationships that could have appeared to in uence the work reported in this paper. No funding was received for this study.