Background: This work aimed to identify the mathematical model and ecological determinants of COVID-19 infection and mortality across different countries during the first six months of the pandemic. Methodology: In this study, authors used the online available data sources of randomly selected 18 countries to figure out potential determinants of COVID-19 transmissibility and mortality. The studied variables were environmental factors (daily average temperature, daily humidity), socioeconomic attributes (population age structure, count and density, human development index, per capita income (PCI), gross domestic product, internet coverage) mobility trends and chronic diseases. Researchers used the linear and exponential time series analysis, and further utilized multivariate techniques to explain the variance in the monthly increase in cases and deaths. Results: In the first two months, the R2 of linear models for the cases and deaths were higher than that of the corresponding R2 of the exponential model. Later one, R2 of the exponential model was occasionally relatively higher than that of the linear model. The exponential growth rate of new cases was significantly associated with mobility trends (β = 0.00398, P = 0.002), temperature (β = 0.000679, P = 0.011), humidity (β = 0.000249, P < 0.001), and the proportion of population aged ≥65 years (β = -0.000959, P = 0.012). Similarly, the exponential growth rate of deaths was significantly associated with mobility trends (β = 0.0027, P = 0.049), temperature (β = 0.0014, P < 0.001), humidity (β = -0.0026, P < 0.001), and PCI of countries. During this period, COVID-19 transmissibility was evident to be controlled as soon as social mobility is decreased by about 40% of the baseline over 3 months controlling for the other predictors. Conclusion: Controlling of COVID-19 pandemic is based mainly on controlling social mobility. Role of environmental determinants like temperature and humidity was well noticed on disease fatality and transmissibility. Socio-demographic determinants of COVID-19 spread and fatality included modifiable risk factors like PCI and non-modifiable risk factors like ageing.
