Using BCG vaccination to protect against COVID-19: when reality fails to meet expectation

While anticipating the development of a COVID-19-specific vaccine, several randomized controlled trials (RCTs) explored the potential of BCG vaccination to protect against COVID-19, based on trials demonstrating beneficial effects of BCG vaccination on unrelated infections and all-cause mortality in neonates in high-mortality geographical settings. Results are now available from 12 RCTs, which suggest that BCG vaccination is not an effective intervention against COVID-19. That the BCG–COVID-19 trials failed to meet expectation emphasizes the importance of rigorous clinical trials to validate hypotheses, even in urgent situations such as a pandemic.