Social distancing, temperature, BCG and the evolution of COVID-19: a panel-model analysis

Background: This work presents results concerning the impact of some variables mentioned in the literature on the daily variation rate of cases (per million inhabitants) of COVID-19, based on a large sample of countries and an empirical model with appropriate control factors. We also propose indicators for measuring social distancing and BCG (Bacilo Calmette-Guerin) vaccine immunization. Methods: A statistical panel-model was applied to daily data for 165 countries from January 22 to July 31, 2020. Besides, two indicators are constructed for each country in the sample. The first of them measures social distancing, based on percentage of people circulating on transport stations, as a proportion of the circulation in a period before pandemic. The second indicator proposed estimates the current percentage of people immunized by BCG vaccine, based on the historical coverage and demographic factors. Results: We estimate that a strict social distancing may be associated with a reduction of around 6 percentage points in the daily variation rate of cases per million of COVID-19. Besides, the effects of temperature and BCG immunization proved to be statistically significant at the usual levels, indicating that lower temperatures and a low (or a lack of) BCG immunization may be related to increases in the daily variation rate of cases (per million inhabitants) of COVID-19. Conclusions: The analysis made clear the role of social distancing to control the pandemic. In addition, the method used did not allow to exclude the hypothesis that the evolution of COVID- 19 may be positively associated with lower temperatures and a low (or a lack of) BCG immunization.