Conclusions
Our study, by integrating a wide set of controls, attenuates if not
eliminates altogether the effects of possible confounding factors
affecting previous studies on BCG and Covid-19. The nonlinear,
probabilistic methods used in the analyses confer additional statistical
robustness to the results. This way, we are able to confirm a robust and
large effect of BCG vaccination on Covid-19 diffusion and mortality, and
to uncover other noteworthy and potentially relevant statistical
relationships. In this wider context, the association between BCG
vaccination and Covid-19 diffusion and mortality is fully addressed by a
comprehensive epidemiological perspective, that can support novel
hypothesis as well as clinical or experimental studies in the field.