Abstract
Tuberculosis vaccines (Bacillus Calmette-Guérin, BCG) were introduced 100 years ago and are still recommended by the World Health Organization to prevent the disease. Studies have shown that BCG vaccination can stimulate non-specific immune responses and reduce the incidence of certain diseases. At the beginning of the coronavirus disease 2019 (COVID-19) pandemic, it was hypothesised that the incidence of COVID-19 was lower in countries with BCG prevention. In an attempt to verify this thesis, we conducted a multicenter, randomised, double-blind, placebo-controlled study on a group of 695 health care workers aged 25 years and over in Poland. All participants in the study had a tuberculin test, after which those who were negative were randomised (1:1) and received either the BCG- or placebo vaccine. From then on, these people were subjected to three months of observation for the occurrence of COVID-19 symptoms. The statistical analysis did not reveal any significant correlation between the frequency of incidents suspected of COVID-19 and BCG-10 vaccination, the result of the tuberculin test and the number of scars. The only statistically significant feature was the type of medical profession-nurses became infected more often than doctors or other medical workers (p = 0.02). The results differ from similar trials in other countries. Perhaps this is due to the lack of an unvaccinated control group. The impact of BCG vaccination on the course of COVID-19 requires further research.