Putting life into a much talked about theory, two independent studies including one carried out by researchers at Jawaharlal Nehru University, here have shown that countries with an active Bacillus Calmette-Guérin vaccination programme have much reduced Covid-19 incidence and lower death rates.
This was a popular hypothesis since in the early days of the pandemic but detailed analysis of data now brings out the scientific evidence to support the theory.
An anti-tuberculosis vaccine, BCG has been part of independent India’s universal immunisation programme since 1948. Many Asian and few European countries also use BCG, but several rich nations either dropped it from their immunisation portfolio or never used it. The USA belongs to the last group.
To check the impact of BCG vaccinations, researchers at JNU in collaboration with the National Institute of Malaria Research, Delhi and several other research institutes compared the Covid-19 prevalence and casualty statistics in nations with a BCG programme with those without the vaccine and a discontinued programme.
The researchers also compared the three groups on the basis of age-wise prevalence and mortality among Covid-19 patients. BCG emerged the winner in every category.
The number of infected cases across the age groups is always higher for countries without universal BCG vaccination policy.
The differences between countries with universal BCG vaccine policy and countries without such a policy increase and reach their peak for age groups 45–64 and 65–79 years. The difference in the number of confirmed cases in these age groups is about 550–600 per million population.
With increasing age, the death toll rises for nations without or discontinued BCG programmes. In comparison, the mortality is quite consistent and rises only slightly in the elderly population in countries with a BCG vaccination programme.
"Experiments have shown that BCG gives protection against respiratory diseases. The immunity, however, is not a specific immunity. It is trained immunity,” lead investigator Gobardhan Das, a professor at JNU told DH.
Das and his colleagues are now modifying the BCG vaccine with a Covid-19 protein aiming for a repurposed use of the age-old shot.
Published in the journal Cell Death and Disease, the study that uses data till May 29th shows that countries without a universal BCG policy (such as Belgium, Italy, the USA, and the Netherlands) have increased incidence of Covid-19 (2810.9 ± 497.1 per million) compared with countries with ongoing national BCG policy (570.9 ±155.6 per million). The incidence for countries that discontinued BCG vaccination was intermediate between these two groups.
Brazil, however, is an exception as it has a very high incidence of Covid-19 incidence and mortality though it used BCG in the immunisation programme. “This may be due to the ineffectiveness of the BCG-Brazil strain,” Das said.
A second study by US researchers demonstrated that among socially similar European countries Covid-19 mortality was negatively correlated with the BCG index, an estimate of the degree to which a country has deployed a universal BCG vaccination program against tuberculosis.
The study that was published in the Proceedings of the National Academy of Sciences last Friday, too supports the hypothesis of an indirect protective effect of BCG vaccination against severe Covid-19 affected patients, while underscoring the need for further research.