Abstract
Protective variables for Coronavirus Disease 2019 (COVID-19) are unknown. “Trained immunity” of the populace as a result of Bacille Calmette–Guérin (BCG) vaccination policy implementation and coverage had been suggested to be one of the factors responsible for the differential impact of COVID-19 on different countries. Several trials are underway to evaluate the potential protective role of BCG vaccination in COVID-19. However, the lack of clarity on the use of appropriate controls concerning the measures of “trained immunity” or the heterologous cell-mediated immunity conferred by BCG vaccination has been a cause of concern leading to more confusion as exemplified by a recently concluded trial in Israel that failed to find any protective correlation with regard to BCG vaccination. Whereas, when we analyze the COVID-19 epidemiological data of European countries without any regard for BCG vaccination policy but with similar age distribution, comparable confounding variables, and the stage of the pandemic, the prevalence of tuberculin immunoreactivity—a measure of cell-mediated immunity persistence as a result of Mycobacterium spp. (including BCG vaccine) exposure of the populations—is found consistently negatively correlated with COVID-19 infections and mortality. We seek to draw attention toward the inclusion of controls for underlying “trained immunity” and heterologous cell-mediated immunity prevalence that may be preexisting or resulting from the intervention (e.g., BCG vaccine) in such trials to arrive at more dependable conclusions concerning potential benefit from them.
Highlights
PLOS PATHOGENSOPINION “Trained immunity” from Mycobacterium spp. exposure or Bacille Calmette–Guerin (BCG) vaccination and COVID-19 outcomes
Early-stage comparisons of the impact could be marred with changing local public policies and adherence to them
The strength of the assertion lies in the large affected study population, i.e., 1,413,367 COVID-19 patients [23]; representing 20 different % LTBI prevalence groups/populations from countries ranging from never ever to current mandatory Bacille Calmette–Guerin (BCG) vaccination policy; comparable health infrastructure, screening and reporting guidelines along with similar age and sex distribution, and other confounding variables
Summary
OPINION “Trained immunity” from Mycobacterium spp. exposure or BCG vaccination and COVID-19 outcomes. OPEN ACCESS Citation: Singh S, Maurya RP, Singh RK (2020) “Trained immunity” from Mycobacterium spp. exposure or BCG vaccination and COVID-19 outcomes.
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