Bacille Calmette-Guerin (BCG) vaccine and potential cross-protection against SARS-CoV-2 infection - Assumptions, knowns, unknowns and need for developing an accurate scientific evidence base

After a century of controversies on its usefulness in protection against TB, underlying mechanisms of action, and benefits in various groups and geographical areas, the BCG vaccine is yet again a focus of global attention- this time due to the global COVID-19 pandemic caused by the novel severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Recent studies have shown that human CD4+ and CD8+ T-cells primed with a BCG-derived peptide developed high reactivity to its corresponding SARS-CoV-2-derived peptide. Furthermore, BCG vaccine has been shown to substantially increase interferon-gamma (IFN-g) production and its effects on CD4+ T-cells and these non-specific immune responses through adjuvant effect could be harnessed as cross protection against severe forms of COVID-19.The completion of ongoing BGG trials is important as they may shed light on the mechanisms underlying BCG-mediated immunity and could lead to improved efficacy, increased tolerance of treatment, and identification of other ways of combining BCG with other immunotherapies. (C) 2021 The Authors. Published by Elsevier Ltd on behalf of International Society for Infectious Diseases.

Automated summary

The BCG vaccine has been a subject of controversy for years, but recent studies suggest it may provide cross protection against severe forms of COVID-19. Ongoing trials could shed light on the mechanisms underlying BCG-mediated immunity, potentially leading to improved efficacy and increased tolerance of treatment.