New York, Aug 10 (IANS): Amid longstanding debate on the effectiveness of the popular tuberculosis (TB) vaccine Bacille Calmette-Guerin (BCG), a new study published in The Lancet Global Health suggests that the jab is protective against the disease only in children under the age of five, and not in adolescents and adults.

BCG is one of the most widely-administered vaccines across the globe. Nearly 100 years old, it is the only vaccine ever administered to treat TB, which afflicts more than 10 million people each year.

BCG vaccination at birth does provide significant protection against TB -- but only in children under five years of age. But that protectiveness may begin to wane as children get older, said researchers at Boston University School of Public Health (BUSPH).

They noted that children over 10 years old and adults should receive a booster BCG vaccine -- and eventually a new, supplemental vaccine, as the BCG booster may also have limited efficacy -- for immunity against TB beyond childhood.

"Unlike many of the mRNA Covid-19 vaccines, which we know are highly effective, there is widespread debate on the BCG vaccine's effectiveness and duration of protection, as well as whether the vaccine only works in selective settings," said lead author Leonardo Martinez, Assistant Professor of epidemiology at BUSPH.

"Our findings indicate that BCG vaccination is effective at preventing tuberculosis in young children. Since tuberculosis in children is a highly debilitating and severe disease, BCG vaccination should continue to be used," he added.

However, since the results show that the vaccine was ineffective in adolescents and adults, "boosting immune protection is needed for older populations," Martinez said. "Novel vaccines are urgently needed to supplement BCG vaccination in high-burden settings."

The findings are based on new analysis that presents data over the past 10 years, from high-burden settings in 17 countries, including South Africa, China, Vietnam, Indonesia, Uganda, The Gambia, and Brazil.

For the study, the team analysed individual-level data from 26 longitudinal studies that included nearly 70,000 participants exposed to TB from 1998 to 2018.

Among all children under 5 years old, BCG vaccination was 37 per cent effective. The researchers did not find conclusive evidence that the vaccine was protective among children over 10 or among adults. When focusing only on pulmonary TB, BCG vaccination was 19 per cent effective, however this effect was also only among young children.