BCG vaccine can control spread: Study
Countries where people have been mandatorily immunised with the Bacillus Calmette–Guerin (BCG) vaccine to prevent childhood tuberculosis reported fewer Covid-19 infections as well as deaths in the first month of their outbreak, according to a new, peer-reviewed study that offers fresh insight into why some countries such as India may be doing better than some major countries in tackling the coronavirus.
The role of the BCG vaccine has been linked to milder Covid-19 infections previously, but the study reviewing infection and fatality numbers from over 130 countries shows for the first time that regions with no BCG immunisation policy since 2000 recorded an exponential increase in deaths due to Covid-19.
The analysis “revealed a significant effect of mandated BCG policies on the growth rate of both cases and deaths after controlling for median age, gross domestic product per capita, population density, population size, net migration rate, and various cultural dimensions (e.g., individualism). Our analysis suggests that mandated BCG vaccination can be effective in the fight against Covid-19,” said the researchers from University of Michigan in the study published on July 31 in the American Association for the Advancement of Science (AAAS) journal.
By applying a statistical model based on their findings, the researchers further estimated that only 468 people would likely have died from Covid-19 in the US as of March 29, 2020 – which is 19% of the actual figure of 2,467 deaths by that date – if the US had mandatory BCG vaccinations several decades ago.
The BCG vaccine has been given to children since 1949 and in 2019, at least 97% of the 26 million babies born that year received it. The vaccine protects against disseminated TB and meningitis in childhood, but doesn’t offer protection from adult pulmonary TB, which has led to several countries discontinuing its use.
The researchers note that the benefits were seen in countries that had the policy in place till about the year 2000. “Notably, the growth curves were as steep in countries that mandated BCG policies only during the 20th century as in those that never mandated the vaccine… That is to say, the spread of the virus may be slowed only when there is “herd immunity” that prevents the virus from spreading easily across the population,” they added.
The study took three specific approaches to rule out external bias, the researchers added. “First, we focused on the rate of growth of both cases and deaths, which should be uninfluenced by reporting biases as long as these biases are stable during the period of study. To meet this requirement, we focused on a short period (either the first 30 days or 15 days). Second, we used the best available estimate of country-wise reporting biases and used this as a weight in our analysis. Third, we controlled for testing availability,” they said.
But, the findings also showed there was substantial variation in Covid-19 growth rates even among BCG-mandated countries, suggesting that additional societal variables are likely have an effect on mandatory BCG vaccination’s effect on the spread of the coronavirus. Thus, “BCG is by no means a magic bullet that assures safety against Covid-19,” the authors added.
On July 18, the Indian Council of Medical Research-National Institute for Research in Tuberculosis (ICMR-NIRT) announced it has initiated a multi-centric study to see if the BCG vaccine can reduce the severity of Covid-19 among people aged 60 and above residing in hot spots for the coronavirus outbreak.
According to the statement, the study will involve around 1,000 healthy volunteers above 60 years of age in six states that have reported a high Covid-19 disease burden so far. “A lot is being talked about the protective effect of BCG vaccine in terms of Covid-19. This study was in the pipeline for some time and now we have begun the process. It is being done to generate India-specific evidence,” said an ICMR official, who did not wish to be identified.