According to a preliminary study posted on medRxiv, the countries that have mandatory policies requiring citizens to get the Bacillus Calmette Guerin (BCG) vaccine to fight tuberculosis have registered fewer coronavirus deaths than countries that don't have vaccination policies. However a randomised clinical trial (RCT) is required to determine this. Already, such tests are being conducted among healthcare in the Netherlands and Australia.
However to the study. Firstly heterologous immunity induced by BCG has been shown to last for nearly two years. Since BCG vaccination is predominantly administered to children, BCG associated immunity may not be responsible for reduced COVID-19 morbidity in adults and the elderly.
Though RCTs are taking place, the results will still be confounded by the different epidemic control strategies implemented by each country.
Further epidemiological results can be "confirmed" by testing the hypothesis when the epidemic "matures" in low-income countries.
The BCG vaccine is one of the most widely used vaccines in immunisation of more than 80% of neonates and infants. Its benefits have been well documented in the treatment of diseases like meningitis and disseminated TB in children.
The BCG vaccine which most Indians are given at birth to prevent tuberculosis, is now being considered for healthcare workers to protect them from coronavirus. The trials kickstarted a wee ago and are being carried out by a children's hospital in Australia and their colleagues in the Netherlands and Germany.
In the initial trials, it was found that in the first year of life, BCG vaccine, besides its protection against TB, was also found to be protective against other viruses similar to SARS CoV-2. There was a reduction in severity of symptoms. The trials have been expedited to buy time till a new vaccine for COVID19 becomes available.Vaccines generally raise immune responses specific to a targeted pathogen, such as antibodies that bind and neutralise one type of virus but not others.
BCG can remain alive in the human skin for up to several months. It 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 among the elderly. A vaccine probably will not eliminate infections with the new coronvirus completely, but is likely to dampen its impact on individuals.
BCG had been found to demonstrate a non-specific protective effect against infections in children. particularly respiratory infections.Further, vaccines for measles and oral polio are too thought to have non-specific beneficial effects on some infections. There is a possibility that BCG could reduce the intensity of COVID infection by stimulating the memory of innate immunity.
Currently, there are no proven studies which validate the effectiveness of BCG vaccine in the treatment of coronavirus. Scientists have contended that it will still take several months to get results from trials. This may be particularly useful for frontline workers to reduce the severity of Covid-19 infection.