COVID-19 transmission risk factors
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We analyze risk factors correlated with the initial transmission growth rate of the COVID-19 pandemic. The number of cases follows an early exponential expansion; we chose as a starting point in each country the first day with 30 cases and used 12 days. We looked for linear correlations of the exponents with other variables, using 126 countries. We find a positive correlation with high C.L. with the following variables, with respective p-value: low Temperature (4·10^-7), high ratio of old vs. working-age people (3·10^-6), life expectancy (8·10^-6), number of international tourists (1·10^-5), earlier epidemic starting date (2·10^-5), high level of contact in greeting habits (6 · 10^-5), lung cancer (6 · 10^-5), obesity in males (1 · 10^-4), urbanization (2·10^-4), cancer prevalence (3 · 10^-4), alcohol consumption (0.0019), daily smoking prevalence (0.0036), UV index (0.004, smaller sample, 73 countries), low Vitamin D levels (p-value 0.002-0.006, smaller sample, ∼ 50 countries). There is highly significant correlation also with blood type: positive correlation with RH- (2·10^-5) and A+ (2·10^-3), negative correlation with B+ (2·10^-4). We also find positive correlation with moderate C.L. (p-value of 0.02∼0.03) with: CO_2 emissions, type-1 diabetes, low vaccination coverage for Tuberculosis (BCG). Several such variables are correlated with each other and so they likely have common interpretations. We also analyzed the possible existence of a bias: countries with low GDP-per capita, typically located in warm regions, might have less intense testing and we discuss correlation with the above variables.
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