Association of BCG vaccination policy and tuberculosis burden with incidence and mortality of COVID-19

Background Evidence suggests non-specific benefits of the tuberculosis vaccine bacillus Calmette-Guérin (BCG) against non-related infections. Recent studies propose such protection may extend to the novel COVID-19 as well. This is a contested hypothesis. Methods Our ecological study confronts this hypothesis. We examine the effects of BCG vaccination on countries’ COVID-19 (a) cases and deaths (per million) and (b) exponential growth factors over specific periods of the pandemic. Since the BCG vaccine was derived from Mycobacterium bovis, a bacterium causing tuberculosis in cattle, having suffered from tuberculosis also may exert a non-specific protection against the COVID-19 as well. Along with BCG vaccination, we test the effect of the prevalence of tuberculosis. We employ multiple regression and principal component analysis (PCA) to control for potentially confounding variables ( n = 16). Results BCG vaccination policy and incidence of tuberculosis is associated with a reduction in both COVID-19 cases and deaths, and the effects of these two variables are additive (≈ 5% to 15% of total unique variance explained). The study of exponential growth factors in the initial stages of the pandemic further shows that BCG vaccination exerts a significant effect (up to 35% of unique variance explained). Conclusions Overall, these findings corroborate the hypothesis that BCG vaccination and exposure to tuberculosis may induce a non-specific protection against the novel SARS-CoV-2 infection, even after accounting for a large number of confounding influences. However, given the potential public-health benefits, our results indicate that the hypothesis deserves further attention and should not be hastily dismissed.