New Delhi: Mandated BCG vaccination can effectively help control the spread of Covid-19 infections as well as reduce the death rate, a new study has found.
Bacillus Calmette-Guérin vaccine was developed in 1919 to fight tuberculosis (TB), an infectious respiratory disease. The vaccine was first used on humans in 1921.
During the early pandemic days, studies showed that there is a correlation between countries that have mandated BCG vaccinations and the spread of the disease.
Last month, a study conducted by JNU researchers stated that countries that had vaccinated their population with BCG had a lower Covid-19 spread.
However, experts had said these correlation studies were not enough evidence to make a case for using BCG vaccines as a prevention against Covid-19.
But in the latest study published in the journal Science on 31 July, University of Michigan researchers said the early studies on the BCG vaccine did not address the effects of reporting bias.
This means those studies only compared the absolute number of cases between countries and did not take into account the fact that some countries might be testing less, or under-reporting cases.
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This method also ignored the fact that for some countries, the infection might have arrived sooner, according to the researchers.
Slow rate of infection and deaths
The researchers have used the rate of increase in both confirmed cases and deaths during an early period of country-wise outbreaks, and examined whether this rate might be slower in countries that mandated BCG vaccination at least until 2000.
The study found an increase in both infection and death rates in countries with mandated BCG vaccine policy to be slower.
“The effect we demonstrate is quite substantial,” the researchers wrote in the study.
“For example, our model estimates that the total number of Covid-19 related deaths in the US as of March 29, 2020 would have been 468 — 19% of the actual figure (2,467) — if the US had instituted the mandatory BCG vaccination several decades earlier.”
They added that the available evidence suggests “BCG has beneficial effects on immunity against a range of lung-related infections that go beyond tuberculosis, which makes it a promising candidate for defending against Covid-19”.
Experts had earlier said only clinical trials can prove the efficacy of the vaccine against Covid-19. India last month started clinical trials to test whether BCG vaccine can prevent Covid-19.
A 2017 study published in The BMJ journal had suggested that BCG vaccination lowered overall death rates among children under five.
Another study, published in 2018, showed that BCG vaccination caused genome-wide ‘reprogramming’ of human monocytes — a type of white blood cells involved in immune response — which in turn predicts protection against experimental viral infection.
Limitations
The researchers reported several limitations to their study.
“In all national policies, BCG is given early in life, typically at birth. It remains unclear whether BCG vaccination might be effective when given to adults. Nor is it known how long BCG vaccination might provide immunity to Covid-19 although it is effective against tuberculosis and lung cancer for several decades,” the researchers noted.
They added that it is uncertain if BCG might have any adverse effects when given to those already infected with Covid-19, which is why there is an urgent need for randomised clinical trials.
Moreover, the rates of growth of infections vary substantially across countries that have mandated BCG vaccination.
“Hence, BCG is by no means a magic bullet that assures safety against Covid-19,” the authors said.
However, the researchers justified the need for a thorough investigation of the merit of the mandatory BCG vaccination in the fight against Covid-19.
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