Could BCG Vaccination Induce Protective Trained Immunity for SARS-CoV-2?

Camila Covián,Susan M Bueno,Angello Retamal-Díaz,Alexis M Kalergis

doi:10.3389/fimmu.2020.00970

Abstract

Trained immunity is a type of non-specific memory-like immune response induced by some pathogens and vaccines, such as BCG, which can confer antigen-independent protection against a wide variety of pathogens. The BCG vaccine has been extensively used to protect against tuberculosis for almost a 100 years. Interestingly, this vaccine reduces children's mortality caused by infections unrelated to Mycobacterium tuberculosis infection, a phenomenon thought to be due to the induction of trained immunity. The SARS-CoV-2 pandemic has infected, as of April 22, 2020, 2,623,231 people globally, causing a major public health problem worldwide. Currently, no vaccine or treatment is available to control this pandemic. We analyzed the number of positive cases and deaths in different countries and correlated them with the inclusion of BCG vaccination at birth in their national vaccination programs. Interestingly, those countries where BCG vaccination is given at birth have shown a lower contagion rate and fewer COVID-19-related deaths, suggesting that this vaccine may induce trained immunity that could confer some protection for SARS-CoV-2.

Highlights

Vaccines are considered one of the most important public health achievements of science and medicine, saving the lives of millions of people as well as being one of the most impactful measures against preventing disease [1, 2].Vaccines stimulate the activation of the adaptive immune response and the development of immunological memory, consisting of antigen-specific T and B cells that protect against infections by pathogens [3, 4]
Since Bacillus Calmette-Guérin (BCG) is a specific vaccine against M. tuberculosis infection [42], and it has been shown to induce the development of trained immunity [23], these data suggest a crucial role for this vaccine in the development of unspecific memory against respiratory viruses, like SARS-CoV-2
Along these lines, based on its safety as a vaccine in large populations, BCG could be considered for its broad availability and low cost as a good strategy for the development of trained immunity and, in consequence, protection against novel pathogens in the case of a pandemic

Summary

INTRODUCTION

Vaccines are considered one of the most important public health achievements of science and medicine, saving the lives of millions of people as well as being one of the most impactful measures against preventing disease [1, 2]. These data are in accordance with very recent results showing an inverse correlation between BCG vaccination and COVID-19 incidence and mortality [41] These data suggest that BCG vaccination prevents SARS-CoV-2 infection and reduces the probability of developing a severe case of the disease, improving survival rates [41]. Since BCG is a specific vaccine against M. tuberculosis infection [42], and it has been shown to induce the development of trained immunity [23], these data suggest a crucial role for this vaccine in the development of unspecific memory against respiratory viruses, like SARS-CoV-2. BCG vaccination policy correlates with a better tendency toward lower death mortalities and diminished contagion rates Based on these observations, we hypothesize that BCG vaccination at birth could induce a trained immunity state which could activate a more efficient immune response in SARS-CoV-2 infection

CONCLUDING REMARKS

Findings

DATA AVAILABILITY STATEMENT