Role of Bacillus Calmette-Guérin (BCG) vaccination in protection against COVID-19
Bacillus Calmette-Guérin (BCG) vaccine contains a live attenuated strain of Mycobacterium Bovis, which is globally used to prevent Tuberculosis (TB) (Luca & Mihaescu, 2013). In a recent epidemiological study, Miller et al. described that the severity of the COVID-19 pandemic is more devastating in countries that do not have a universal BCG vaccination policy (USA, Italy) compared to countries that implement BCG vaccination at birth as a part of their routine vaccine policy for new borns (China, India, Portugal). Several pieces of evidence suggest that BCG vaccination provides protection against various DNA and RNA viruses that causes lower respiratory tract infections including Influenza virus (Moorlag, Arts, van Crevel & Netea, 2019). It is probable that BCG vaccine mediated ’the trained immunity’ plays a vital role in providing partial non-specific protection against SARS-CoV-2. The trained immunity involving innate immune memory confers protection against secondary infections independent of the adaptive immune response (Covian et al., 2019). It was reported that innate immune cells like macrophages and natural killer cells (NK cells) involved in the development of ’the trained immunity’ are functionally reprogrammed through epigenetic changes mediated by NOD2 that involves histone methylation (H3K4me3) to develop non-specific protection against viral infections after BCG vaccination (Kleinnijenhuis et al., 2012). To understand BCG vaccine-mediated protection against SARS-CoV-2 infection and or reduction in the severity of COVID-19, two open-label clinical trial were initiated in Australia and Netherlands. These trials are recruiting frontline health care providers who are providing medical support to patients suffering from COVID-19 (NCT04327206 and NCT0432844). The final outcome of these trials will provide more insight into the molecular mechanism of BCG vaccine-mediated protection against COVID-19.