Using BCG vaccine to enhance non-specific protection of health care workers during the COVID-19 pandemic: a randomized controlled trial

Background. The BCG (Bacillus Calmette-Guérin) vaccine can induce nonspecific protection against unrelated infections. We aimed to test the effect of BCG on absenteeism and health of Danish health care workers (HCWs) during the coronavirus disease 2019 (COVID-19) pandemic. Methods. A single-blinded randomized controlled trial included 1221 HCWs from 9 Danish hospitals. Participants were randomized 1:1 to standard dose BCG or placebo. Primary outcome was days of unplanned absenteeism. Main secondary outcomes were incidence of COVID-19, all-cause hospitalization, and infectious disease episodes. Results. There was no significant effect of BCG on unplanned absenteeism. Mean number of days absent per 1000 workdays was 20 in the BCG group and 17 in the placebo group (risk ratio, 1.23; 95% credibility interval, 0.98–1.53). BCG had no effect on incidence of COVID-19 or all-cause hospitalization overall. In secondary analyses BCG revaccination was associated with higher COVID-19 incidence (hazard ratio [HR], 2.47; 95% confidence interval [CI], 1.07–5.71), but also reduced risk of hospitalization (HR, 0.28; 95% CI, .09–.86). The incidence of infectious disease episodes was similar between randomization groups (HR, 1.09; 95% CI, .96–1.24). Conclusions. In this relatively healthy cohort of HCWs, there was no overall effect of BCG on any of the study outcomes.