DOI: 10.7910/dvn/gsenek
title: Mathematical models of Covid-19 mortality based on geographic latitude, climate, and population factors point to a possible protective effect of UV light against the SARS-CoV-2

description: ABSTRACT
Background : The Covid-19 pandemic has caused very high death tolls across the world in the last two years. Geographic latitude, climate factors, and other human related conditions such as epidemiologic and demographic history are taught to have played a role in the prevalence of Covid-19.
Objective : This observational study aimed to investigate possible relations between geographic latitude-associated climate factors and Covid-19 death numbers in 29 countries. The study also aimed to investigate the relationship between geographic latitude and the history of epidemiologic (cancer, Alzheimer's disease) and demographic factors (birth rate, mortality rate, fertility rate, people aged 65 and over), as well as alcohol intake habits. And finally, the study also aimed to evaluate the relationships between epidemiologic and demographic factors, as well as alcohol intake habits with Covid-19 deaths.
Methods : We sought the Covid-19 death toll in 29 countries in Europe, Africa, and the Middle East (located in both hemispheres and between the meridian lines "-15°" and "+50°"). We obtained the death numbers for Covid-19 and other geographic (latitude, longitude) and climate factors (average annual temperature, sunshine hours, and UV index) and epidemiologic and demographic parameters as well as data on alcohol intake per capita from official web pages. Based on records of epidemiologic and demographic history, and alcohol intake data, we have calculated a General Immune Capacity (GIC) score for each country. Geographic latitude and climate factors were plotted against each of Covid-19 death numbers, epidemiologic and demographic parameters, and alcohol intake per capita. Data was analysed by simple linear regression or polynomial regression. All statistical data was collected using Microsoft Excell software (2016).
Results : Our observational study found higher death numbers in the higher geographic latitudes of both hemispheres, while lower scores of deaths were registered in countries located around the equator line and low latitudes. When the Covid-19 death numbers were plotted against the geographic latitude of each country, an inverted bell-shaped curve was obtained (coefficient of determination R2=0.553). In contrast, bell-shaped curves were obtained when latitude was plotted against annual average temperature (coefficient of determination R2= 0.91), average annual sunshine hours (coefficient of determination R2= 0.79) and average annual UV index (coefficient of determination R2= 0.89). In addition, plotting the latitude of each country against the General Immune Capacity score of each country gave an inverted bell-shaped curve (coefficient of determination R2=0.755). Linear regression analysis of the General Immune Capacity score of each country and its Covid-19 deaths showed a very significant negative correlation (coefficient of determination R² = 0,71, p=6.79x10-9). Linear regression analysis of the Covid-19 death number plotted against the average annual temperature temperature and the average annual sunshine hours or the average annual UV index gave very significant negative correlations with the following coefficients of determination: (R2 = 0.69, p = 1.94x10-8), (R2 = 0.536, p = 6.31x10-6) and (R2 = 0.599, p = 8.30x10-7), respectively. Linear regression analysis of the General Immune Capacity score of each country plotted against its average annual temperature temperature and the average annual sunshine hours or the average annual UV index gave very significant negative correlations, with the following coefficients of determination: (R2 = 0.86, p = 3.63x10-13), (R2 = 0.69, p = 2.18x10-8) and (R2 = 0.77, p= 2.47x10-10), respectively. 
Conclusion : The results of the present study prove that at certain geographic latitudes and their three associated climate parameters are negatively correlated to Covid-19 mortality. On the other hand, our data showed that the General Immune Capacity score, which includes many human related parameters, is inversely correlated to Covid-19 mortality. Likewise, geographic location and health and demographic history were key elements in the prevalence of the Covid-19 pandemic in a given country. On the other hand, the study points to the possible protective role of UV light against Covid-19. The therapeutic potential of UV light against the Covid-19 associated with SARS-Cov-2 is discussed.