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.