The influence of vaccination against tuberculosis with the Bacillus-Calmette-Guérin(BCG) vaccine on COVID-19 incidence and mortality – review of the literature

THE AIM OF THE STUDY. Is to present the state of knowledge from April and May 2020 about the influence of Bacillus-Calmette-Guérin vaccination against tuberculosis on incidence and mortality due to COVID-19. MATERIAL AND METHODS. A review of the latest literature till 9 May 2020 has been made. PubMed and ResearchGate databases and WHO reports were used. RESULTS. Immunomodulatory properties of the tuberculosis vaccine which protects against severe cases of tuberculosis and partly against other infections are indicated, including viral and respiratory infections. The BCG vaccine induces heterologous immunity and trained innate immunity. It was noted that in countries which maintain obligatory BCG vaccination COVID-19 incidence and mortality are lower than in countries that have stopped or never introduced BCG as mandatory vaccination. Most analysis confirmed this relationship, but they indicated the possible impact of other factors, such as genetics in the population, the type of strain from BCG vaccine, the level of health care and the wealth of a nation, the structure of migration, co-morbidities and a policy of introducing social distance. CONCLUSIONS. At the moment, we do not have enough evidence to support or deny the hypothesis of COVID-19 reduction in incidence and mortality in countries maintaining obligatory BCG vaccination. Other factors that might affect the results should be considered in further analysis. The results of clinical trials will provide more reliable proofs than analysis of epidemiological data. WHO does not recommend BCG vaccination to prevent COVID-19 and recommends it to newborns from areas with a higher incidence of tuberculosis.