Authored by Dr. Swati Rajagopal, Consultant, Infectious Diseases & Travel Medicine, Aster CMI Hospital.
According to a preliminary study posted on medRxiv, the countries which have mandatory policies to vaccinate against tuberculosis have registered fewer coronavirus deaths than countries who don’t have vaccination policies. This study has now found a correlation between the countries which require citizens to get the bacillus Calmette-Guerin (BCG) vaccine and those showing fewer number of confirmed cases and deaths from Covid-19. However, a randomized clinical trial (RCT) is required to determine this. In line with this RCTs in healthcare workers are on-going in the Netherlands and Australia.
However, there are still some caveats to the study. Firstly heterologous immunity induced by BCG has predominantly been shown to last for nearly 2 years. Since BCG vaccination is predominantly administered to infants and children, BCG-associated heterologous immunity may not be responsible for reduced COVID-19 morbidity in adults and the elderly. Even though these caveats and RCTs are taking place in Netherlands and Australia to determine if BCG confers heterologous immunity against COVID-19, however these results will still be confounded by the different epidemic control strategies implemented by each country. Further epidemiological results presented by Miller et al., can be “confirmed” by testing the hypothesis when the epidemic “matures” in low-income countries.
About BCG Vaccine
The Bacillus Calmette-Guérin (BCG) vaccine is one of the most widely used vaccines in immunization of more than 80% of neonates and infants in countries where childhood immunization is a part of national programme. The benefits of the vaccine have been well documented in treatment of diseases like meningitis and disseminated TB in children. The BCG vaccine is considered only for very select persons who meet specific criteria and in consultation with a TB expert. The BCG vaccine which most Indians are given at birth and is used to prevent Tuberculosis, is now being considered to healthcare workers to protect them in their fight against corona virus.
Does BCG protect against novel corona virus?
The trials for BCG vaccine kick started a week ago and is being carried out by the children hospital in Australia and their colleagues in Netherlands and Germany. In the initial trails, it was found that in the first year of life BCG vaccine besides its protection against TB was found to be protective against other viruses similar to SARS-CoV-2: There was reduction in severity of symptoms. The trials on the effectiveness of BCG vaccine have also been expedited in order to buy time till the new vaccine for SARS-COViD19 – becomes available.
Vaccines generally raise immune responses specific to a targeted pathogen, such as antibodies that bind and neutralize one type of virus but not others. But BCG may also increase the ability of the immune system to fight off pathogens other than the mycobacterium tuberculosis. BCG, can remain alive in the human skin for up to several months, triggers not only Mycobacterium-specific memory B and T cells, but also stimulates the innate blood cells for a prolonged period. It may also enable improved resistance to fight infections in elderly. It is very clearly outlined that vaccine probably won’t eliminate infections with the new coronavirus completely, but is likely to dampen its impact on individuals.
BCG had in the past been found to demonstrate a non-specific protective effect against infections in children, particularly respiratory infections. Furthermore, vaccines for measles and oral polio are too thought to have non-specific beneficial effects on some infections. Therefore, there is a possibility that BCG could reduce the intensity of SARS-CoV-2 infection by stimulating the memory of innate immunity.
Currently, there are no proven studies or reports which validate the effectiveness of BCG vaccine in treatment of coronavirus. Scientist have contended that, it will still take several months to get results from trials testing the BCG vaccine to fight COVID-19. In the past, BCG vaccine was considered to be protective against SARS too – so, we need more evidence and science to understand the protective effect against Covid 19. This may be particularly useful for front line workers to reduce the severity of the infection with Covid 19.