Scientists have found that countries with mandatory Bacillus Calmette-Guérin (BCG) vaccination until at least the year 2000 tended to exhibit slower infection and death rates during the first 30 days of the outbreak of COVID-19 in their country. By applying a statistical model based on their findings, the researchers further estimated that only 468 people would likely have died from COVID-19 in the U.S. as of March 29, 2020 - which is 19% of the actual figure of 2,467 deaths by that date - if the U.S. had instituted mandatory BCG vaccination several decades ago. They established this correlation via statistical analyses that controlled for several potential biases, including differences in the availability of tests, how cases were reported, and the timing of outbreak onset across countries. Their findings suggest that national policies for universal BCG vaccination can be effective in the fight against COVID-19 - an association that merits clinical investigation, the authors say. Available evidence demonstrates that BCG vaccination, typically given at birth or during childhood to prevent tuberculosis, can also help strengthen immunity against various other infectious diseases - perhaps including COVID-19. However, investigating a potential relationship between universal BCG vaccination and spread of the SARS-CoV-2 virus requires accounting for the effects of several biases and variables across countries, which previous studies have not done, the authors say. For example, some past efforts focused on the total number of infections and deaths, which have varied considerably among countries based on when the disease took hold.
Martha Berg and colleagues instead focused on changes in the growth rates of COVID-19 cases and deaths, while controlling for variables including diagnostic test availability, median age, per capita GDP, population size and density, net migration rate, and various cultural differences such as individualism. They analyzed the day-by-day rate of increase of confirmed cases in 135 countries and deaths in 134 countries in the first 30-day period of each country's outbreak. Mandatory BCG vaccination correlated with a flattening of the curve in the spread of COVID-19, the analysis showed. However, the authors caution that their results do not portray BCG as a "magic bullet." They found substantial variation in COVID-19 growth rates even among BCG-mandated countries, suggesting that additional societal variables likely have an effect on mandatory BCG vaccination's effect on the spread of COVID-19. The authors note that this variation must be addressed in future work.