The use of easily accessible live vaccines like Bacillus Calmette–Guérin (BCG), which has shown protective efficacy for other infections, was studied to supplement routine COVID-19 vaccinations, especially in low- and middle-income countries without adequate coverage and access to COVID-19 vaccines

We hypothesised that vaccination with BCG will reduce the incidence and severity of COVID-19 infections in high-risk groups.

This multi-centre quadruple-blind randomised controlled trial showed a significant reduction in the incidence of microbiologically proven (CB-NAAT-positive) severe COVID-19 infections. In addition, it also showed a reduction in the incidence of acute respiratory illness (probable symptomatic COVID-19 infection based on seroconversion rates). However, there was no significant difference in the overall incidence of microbiologically proven (CB-NAAT positive) COVID-19 infection. However, there was a higher COVID-19 seroconversion in the placebo arm compared with the BCG arm at the end of 9 months of follow-up

This study shows that BCG protects high-risk adults between 18 and 60 years of age from symptomatic acute respiratory illness (probable symptomatic COVID-19 infection) and severe disease, like most available COVID-19 vaccines in low- and middle-income countries. However, it does not necessarily reduce the overall incidence of COVID-19 infection.