Unpredictable, Counter-Intuitive Geoclimatic and Demographic Correlations of COVID-19 Spread Rates

SIMPLE SUMMARY: Rates of viral spread during first and second waves of the COVID-19 pandemic for USA states, and for consecutive nonoverlapping periods of 20 days for the USA and 51 countries across the globe associate with mean temperature, elevation, population density and age. Some associations switch directions when comparing different periods. Even population density, which presumably should always increase viral spread, at some periods seems to decrease spread rates. We also observed systematic inversions between spread rates estimated at 80–100 day intervals. These patterns remain unexplained and suggest difficulties in managing and predicting the pandemic, in particular, negative correlations between population density and spread rates, which were observed in independent samples and at different periods. Putatively, confinements could produce these patterns, by selecting viral strains with longer contagiousness and/or latent periods. ABSTRACT: We present spread parameters for first and second waves of the COVID-19 pandemic for USA states, and for consecutive nonoverlapping periods of 20 days for the USA and 51 countries across the globe. We studied spread rates in the USA states and 51 countries, and analyzed associations between spread rates at different periods, and with temperature, elevation, population density and age. USA first/second wave spread rates increase/decrease with population density, and are uncorrelated with temperature and median population age. Spread rates are systematically inversely proportional to those estimated 80–100 days later. Ascending/descending phases of the same wave only partially explain this. Directions of correlations with factors such as temperature and median age flip. Changes in environmental trends of the COVID-19 pandemic remain unpredictable; predictions based on classical epidemiological knowledge are highly uncertain. Negative associations between population density and spread rates, observed in independent samples and at different periods, are most surprising. We suggest that systematic negative associations between spread rates 80–100 days apart could result from confinements selecting for greater contagiousness, a potential double-edged sword effect of confinements.