BCG Revaccination: Can a Second Shot Stop TB in Teens?
- FHS Communications
Tuberculosis (TB) continues to claim lives, especially among young people
With an estimated 1.8 million adolescents and young adults contracting the disease each year. This age group was historically neglected as TB surveillance focused on "children" (aged 0–14 years) and "adults" (aged ≥15 years). Today, scientists are looking to see if a second dose of the BCG vaccine—called revaccination—is the answer to addressing this lag.
Study overview
Researchers conducted a placebo-controlled trial at five sites in South Africa for the paper titled BCG Revaccination for the Prevention of Mycobacterium tuberculosis Infection. They revaccinated 1,836 teens with BCG shots between 2019 and 2021, tracking them for two and a half years. The participants (aged 10–18 years) were HIV-negative and QFT-negative (detects latent or active TB infection). Participants were randomly assigned to the BCG vaccine group or the placebo group to compare the efficacy of Revaccination between the two.
Key findings
The results, published in the New England Journal of Medicine, showed that almost the same number of teens developed TB in both groups—62 with the extra BCG shot, 59 with the placebo. The revaccination sparked an immune response, but it wasn’t enough to protect against the infection. BCG revaccination induced cytokine-positive CD4 T-cell responses that persisted for at least 6 months post-vaccination. The BCG group experienced a higher rate of mild to moderate adverse events, such as swelling (72%), pain (42%) and redness (38%).
Although a prior trial showed 45% efficacy for preventing sustained infection, this trial showed the opposite despite a larger sample size and broader geographic and age inclusion.
This study shows that repeating the original BCG vaccine won’t protect adolescents against TB infection, just as a similar Brazilian study found in revaccinating adult healthcare workers. It is unknown, though, whether there is any protection against TB disease. But there’s a silver lining: understanding what doesn’t work is just as important as knowing what does.
Professor Lee Fairlie, Wits contributing researcher and Director of Maternal and Child Health at the Wits Reproductive Health and HIV Institute (Wits RHI), says further TB vaccine development is needed. “It remains important for us to continue to work towards finding a TB vaccine that has sufficient efficacy to make a substantial impact towards TB prevention.” She explains.
She notes that other studies have made great strides in getting some aspects of their TB vaccine development right, adding promise that there will be a TB vaccine soon. “Although the Gates MRI M72 vaccine, as well as MTBVAC, have progressed furthest in the vaccine pipeline, and we’re hopeful that by 2030 we’ll have at least one TB vaccine ready to be rolled out!”, says Professor Fairlie.