BCG stands for Bacillus Calmette-Guerin. It is a vaccine that provides protection against tuberculosis; it helps build immunity against tuberculosis. However, it is effective in preventing the form of TB that affects the lungs. Covid-19 also eventually affects lungs. So, will it be any relation in between these two vaccines.
In comparing the incidence of COVID-19 cases in countries where the BCG vaccine is used with countries where it is not used, it is observed that countries that routinely used the vaccine in neonates had less reported cases of COVID-19. However, there is no evidence that the BCG vaccine protects people against infection with COVID-19 virus.
So far, there are association studies. BCG vaccine is routinely given in India yet the number of new COVID cases are the highest in India. This makes it unlikely that BCG vaccine will help reducing COVID cases. There are researchers in Australia and Germany enrolling patients for clinical trial.
BCG programs the immune system well but looking at the COVID infection rates from India its unlikely to have a causative effect on COVID 19 where a huge population had already received BCG