Correlation between immunity from BCG and the morbidity and mortality of COVID-19.

Background: To investigate the association between parameters indicating immunity from BCG at country level (presence of BCG vaccination policy, BCG coverage, age-specific incidence of tuberculosis (TB)) and the morbidity and mortality of COVID-19.

Methods: Country-specific data for COVID-19 cases and deaths, demographic details, BCG coverage and policy, age-specific TB incidence and income level were obtained. The crude COVID-19 cases and deaths per 100,000 population were calculated and assessed against the parameters indicating immunity from BCG using linear regression analysis.

Results: Univariate analysis identified higher income level of a country to be significantly associated with COVID-19 cases ( < 0.0001) and deaths ( < 0.0001) but not with its case fatality rate. The association between COVID-19 and TB was strongest for TB incidence in patients > 65-years (Cases (r = - 0.785, = 0.0001)) and deaths (r = - 0.647, = 0.0001).Multivariate analysis identified the higher income level of a country and not having a universal BCG vaccination policy to affect the COVID-19 cases. The deaths were inversely affected by the presence of BCG vaccination policy and coverage; and positively by the TB incidence in patients > 65-years.

Conclusion: Significant inverse correlations observed between cases and deaths of COVID-19 and BCG related parameters highlights immunity from BCG as a likely explanation for the variation in COVID-19 across countries.