Background
Older age is associated with increased severity and death from respiratory infections, including coronavirus disease 2019 (Covid-19). The tuberculosis vaccine Bacille Calmette-Guérin (BCG) may provide heterologous protection against non-tuberculous infections, and has been proposed as a potential preventive strategy against Covid-19.
Methods
In this multicenter, placebo-controlled trial, we randomly assigned elderly individuals (60 years or older, n=2014) to intracutaneous vaccination with BCG (n=1008) or placebo (n=1006). The primary endpoint was the cumulative incidence of respiratory tract infections that required medical intervention, during 12 months of follow-up. Secondary endpoints included the incidence of Covid-19, and the effect of BCG vaccination on the cellular and humoral immune responses.
Results
The cumulative incidence of respiratory tract infection requiring medical intervention was 0.029 in the BCG-vaccinated group and 0.024 in the control group (subdistribution hazard ratio [SHR], 1.26; 98.2% confidence interval [CI], 0.65 to 2.44). 51 and 48 individuals tested positive for SARS-CoV-2 by PCR in the BCG and placebo group, respectively (SHR, 1.053; 95% CI, 0.71 to 1.56). No difference was observed in the frequency of adverse events. BCG vaccination was associated with enhanced cytokines responses after influenza, and partially also after SARS-CoV-2 stimulation. In patients diagnosed with Covid-19, antibody responses after infection were significantly stronger if the volunteers had previously received BCG.
Conclusions
BCG-vaccination had no effect on the incidence of respiratory tract infections, including SARS-CoV-2 infection, in elderly volunteers. However, BCG vaccination improved cytokine responses stimulated by influenza and SARS-CoV-2, and induced stronger antibody titers after Covid-19 infection.
Summary
Bacille Calmette-Guérin (BCG) induces long-term boosting of innate immunity, termed trained immunity, and decreases susceptibility to respiratory tract infections. BCG vaccination trials for reducing SARS-CoV-2 infection are underway, but concerns have been raised regarding the potential harm of strong innate immune responses. To investigate the safety of BCG vaccination, we retrospectively assessed coronavirus disease 2019 (COVID-19) and related symptoms in three cohorts of healthy volunteers who either received BCG in the last 5 years or did not. BCG vaccination is not associated with increased incidence of symptoms during the COVID-19 outbreak in the Netherlands. Our data suggest that BCG vaccination might be associated with a decrease in the incidence of sickness during the COVID-19 pandemic (adjusted odds ratio [AOR] 0.58, p < 0.05), and lower incidence of extreme fatigue. In conclusion, recent BCG vaccination is safe, and large randomized trials are needed to reveal if BCG reduces the incidence and/or severity of SARS-CoV-2 infection.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.