A theory gaining currency in Russia is that people who were vaccinated for Tuberculosis, with a BCG shot, are maybe less susceptible to Covid-19. Russia is among the countries where the bulk of the population has received BCG & it's had only 8 reported coronavirus deaths, so far https://twitter.com/max_katz/status/1244211006206644224

The countries with the yellow-ish color have universal BCG vaccination programs. Notably, Ireland & Portugal, which do widely vaccinate, have considerably lower death rates than their neighbors the UK & Spain who do not. Italy & the US have the most Covid-19 cases.