A study has found that the Bacillus Calmette-Guérin (BCG) vaccine, when administered in infancy, only protects against tuberculosis (TB) in children under five years of age. The findings, published in The Lancet Global Health, showed that the vaccine provided no protection among adolescents or adults in the study.
Despite the age and widespread use of the BCG vaccine, debate continues on how effective it is in preventing TB, and the duration of immunity after it is administered in infancy. And as experts study and propose new TB vaccines to supplement the BCG vaccine, an important consideration is the age at which these new vaccines should be administered to high-risk populations.
Gathered from 20 years of recent studies, this analysis provides new insight and clarity on these issues.
These results suggest that protectiveness from the BCG vaccine may begin to wane as children get older and, thus, children over 10 years old and adults should receive a booster BCG vaccine for immunity against TB beyond childhood. Unfortunately, a BCG booster has limited efficacy, so new vaccines are needed.
“Unlike many of the mRNA COVID 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,” explained study lead author Leonardo Martinez, assistant professor of epidemiology at Boston University School of Public Health. “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.”
However, since the results show that the vaccine was ineffective in adolescents and adults, “boosting immunoprotection is needed for older populations,” Asst Prof Martinez said. “Novel vaccines are urgently needed to supplement BCG vaccination in high-burden settings.”
Most studies on this subject were done over 50 years ago, with varying results, and primarily in settings with a relatively low burden of the disease. This new analysis 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, Asst Prof Martinez and colleagues analysed individual-level data from 26 longitudinal studies that included nearly 70 000 participants exposed to TB from 1998 to 2018. The researchers examined the impact of BCG vaccination for all TB disease, as well as specifically for pulmonary and extrapulmonary TB. The analysis examined variability across the studies, including the use of skin and blood TB infection tests, and accounted for potentially confounding factors such as HIV, exposure status, and history of prior TB, amongst others.
Among all children under 5 years old, BCG vaccination was 37% 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% effective, however this effect was also only among young children.
The researchers stress that substantial investment in TB vaccine development is critical to controlling global TB.
“We urgently need vaccines that are effective against tuberculosis in adults,” said study co-author C. Robert Horsburgh, professor of epidemiology. “There are a number of promising TB vaccine candidates under study and we hope that one or more of them will prove effective.”
Source: Boston University
