New Delhi: Scientists from the ICMR’s National Institute for Research in Tuberculosis (NIRT) in Chennai have shown that administering Bacillus Calmette-Guérin (BCG) vaccine — primarily used against tuberculosis — to elderly individuals can enhance their innate and adaptive immunity, which may help protect against Covid-19.
The study, which is yet to be peer reviewed, is one of the first clinical trials to examine the effect of the BCG vaccine in the context of the coronavirus pandemic.
Since the early days of the pandemic, several studies have suggested that the tuberculosis vaccine, routinely given to children in countries where TB is endemic, may also help protect against Covid.
These claims were based on the fact that countries that had BCG programmes had lower Covid infection and fatality rates compared to countries that did not have so.
In an interview to ThePrint, Gobardhan Das, a professor at Jawaharlal Nehru University (JNU), had highlighted the correlation between the BCG vaccines and low rates of Covid incidence. His team’s research was later published in the Nature journal.
However, at the time, there was a lack of data from clinical trials to support this claim — which led many scientists to dismiss it. World Health Organization (WHO) chief scientist Soumya Swaminathan had also said it was unlikely that the vaccine given in childhood would offer a protective effect to a different virus in adulthood.
Nevertheless, several countries designed clinical trials to test the efficacy of the BCG vaccine against Covid-19.
In the latest study, the ICMR-NIRT researchers found that the vaccine helped improve the innate and adaptive immune responses in elderly people.
The innate immune response is the first to kick in and is common among all animals. It is non-specific and immune cells mount an immediate attack on antigens. The response is subsequently replaced by the adaptive immune response, which tailors defences based on the BCG vaccine kind of pathogen that is being encountered.
The innate immune response consists of white blood cells like neutrophils, macrophages, and monocytes, while the adaptive response involves T cells and B cells (types of white blood cells), as well as antibodies.
The ICMR-NIRT trial involved 86 people aged 60-80 years, who were divided into two groups. Fifty four people received the BCG vaccine, while the 32 others did not. All the participants were followed up after a month.
The team looked at the impact of the vaccine on the frequencies of T cell, B cell, monocyte and dendritic cell — all vital parts of the immune system — as well as total antibody levels.
The study found that BCG vaccination induced enhanced frequencies of memory CD4+ T and CD8+ T cells — which help trigger the signalling protein that mediate an immune response depending on the type of pathogen.
The vaccine also enhanced memory B cells — which can survive for decades and repeatedly trigger antibody-mediated immune response in the case of re-infections.
However, the study only looked at immune system markers, and did not test the participants for Covid. Whether this enhanced adaptive and innate immunity can protect from infections like SARS-CoV-2 still needs to be determined, the researchers acknowledged.
Nevertheless, the data reveals an important role for BCG vaccination in boosting immune responses in the elderly population — which is more vulnerable to severe forms of Covid.
‘Important to examine’
Scientist Gagandeep Kang, professor at Christian Medical College, said the data from ICMR “offers potential mechanistic support for the hypotheses being tested by several BCG and recombinant BCG trials in India and other parts of the world”.
However, more results from existing trials will be required to understand the clinical utility of BCG in the Covid pandemic, added Kang, who was not involved in the study.
“Although this study on 86 elderly individuals at risk of Covid-19 infection suggests that BCG vaccination might boost the immune responses in the elderly population, it is important to examine whether this response would indeed help people acquire improved protective immunity to Covid-19 virus,” said S.P. Kalantri, professor of medicine at the Mahatma Gandhi Institute of Medical Sciences in Wardha, Maharashtra.
Kalantri added that a clinical trial — in which study participants would receive either BCG vaccine or a placebo and be followed to find out if the vaccine recipients are at a lower risk of acquiring Covid infection — could tell if the vaccine helps against the coronavirus, and how much benefit it yields.