Association of BCG vaccination policy with prevalence and mortality of COVID-19

Giovanni Sala; Tsuyoshi Miyakawa

Associations of BCG policy with COVID-19 after controlling two major confounding factors In this study, we have shown that the countries that currently adopt universal BCG vaccination programs (Group A) have, compared to the other countries, a lower number of cases and deaths per one million people. The countries that no longer recommend BCG vaccination for everyone (Group B) and those that have never had universal BCG vaccination programs (Group C) reports more cases and deaths. We have also evaluated the impact of two potentially confounding factors, the country's life expectancy and the average temperature in February and March 2020. Crucially, the effects of BCG groups on the two dependent variables remain significant, even when the country's life expectancy and temperature are controlled for. The amount of variance explained by BCG vaccination is about 12.50% and 20% for cases and deaths per one million population, respectively. The percentage of explained variance is greatly increased when only countries with a life expectancy above 78 years are considered (about 20% and 38% for cases and deaths, respectively). Also, only Group C appears to play a role in the deaths/cases ratio and explains little more than 3% of the observed variance. This latter result may suggest that, unlike cases and deaths per one million population, the death rate is weakly affected by the type of BCG vaccination policy adopted by the country. We thus hypothesize that the protective effect of the vaccine, if any, may consist of a significant reduction of the spread of the virus rather than a reduced mortality rate. It is also possible that the vaccine prevents progression of the disease after infection, since only the persons with severe symptoms tend to be able to receive PCR tests in many of the countries at present. This hypothesis requires additional empirical corroboration. Finally, in line with the results of the linear regression analysis, the Chi-squared analyses highlight that BCG vaccination policy appears to affect how quickly this virus spreads. Taken together, these results suggest that the overall impact of BCG vaccination on the COVID-19related cases and deaths is, at the very least, non-negligible and worth of further empirical investigation.