Nonspecific effects of the Bacillus Calmette-Guerin (BCG) vaccine on mortality and infections

The bacillus Calmette-Guerin (BCG) vaccine used in tuberculosis prevention may lower mortality in babies and children, and prevent infectious diseases other than tuberculosis. Recent studies have suggested that it may also protect against COVID-19 and prevent mortality from this disease. These recent investigations were limited because they only looked at correlations between having a BCG vaccination program and COVID-19 mortality rates. Studies need to be conducted in populations where there are vaccination, disease and mortality registries, so that we know exactly who was vaccinated, who had the disease and who died. In the Province of Quebec, a BCG vaccination campaign took place between 1949 and the mid-1970s. The vaccine was offered for free to newborns and schoolchildren, and vaccination information is compiled in a registry. The goal of our study is to determine if BCG vaccination in early life is associated with decreased mortality and with risk of infections over the life course. We will study selected bacterial and viral infections, and also infections with SARS-CoV-2, the virus causing COVID-19. The study population consists of 400,000 persons. This is almost all individuals born in Quebec between 1970 and 1974. They are now aged 47 to 51 years old. Data was already obtained from provincial administrative databases until 2014, including BCG vaccination status, sociodemographic factors, and death if applicable. We will obtain data on mortality and on use of health services for infections from provincial databases until 2021. We will compare the rates of mortality and of infections (with bacterial and viral infections and with COVID-19 separately) among persons who received the BCG vaccine and those who did not. There are few places in the world where this type of study can be done. Our unique setting will allow us to answer several important questions on BCG vaccination, helping us understand its effects beyond tuberculosis prevention.