100-Year-Old Vaccine for a Novel Virus: Killing Two Birds with One Stone!

Introduction

The coronavirus pandemic has spread like wildfire across the globe. Some countries are more affected than others while children seem to have a milder form of the disease as compared to adults.[1] We are still grappling to understand the reason behind these disparities. There appears to be a correlation between Bacillus Calmette–Guérin (BCG) vaccination and protection against COVID-19.[2],[3] Some experts hypothesize that countries offering BCG vaccine in the national immunization program at birth seem to have a lower death rate from COVID-19.[3] Whether this can be attributed to the BCG vaccine or a less virulent virus strain or social distancing measures or because countries like India are just entering phase III of the epidemic will only be known retrospectively. If BCG is indeed the reason for this protective effect, can it be attributed to persistence of “heterologous” or “off-target” effects of the BCG vaccine, will unfold over the next few months. Banking on the “heterologous effect” of BCG, two clinical trials NCT04327206 and NCT04328441 propose to administer prophylactic BCG vaccine to health-care providers in Australia and the Netherlands respectively. At this point in time, there are 3 trials in the Clinical Trials Registry of India using different BCG strains to harness this heterologous effect against COVID-19. The research hypothesis is activation of the innate immune system to protect against progression of the Coronavirus infection.[4] In this article, we try to understand the underlying mechanisms of immune protection, “trained immunity” conferred by the BCG vaccine and review some epidemiological evidence that support or refute the hypothesis.

Publication History

Received: 15 April 2020

Accepted: 12 May 2020

Article published online:
28 June 2021

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