The Truth About BCG Revaccination

In a groundbreaking study published in the New England Journal of Medicine, researchers reveal that Bacille Calmette-Guérin (BCG) revaccination does not effectively prevent sustained infections from Mycobacterium tuberculosis, a major global health concern.

What the Study Uncovered

Led by Dr. Alexander C. Schmidt from the Gates Medical Research Institute, this phase 2b, double-blind, randomized trial scrutinized the efficacy of BCG revaccination against a placebo in HIV-negative adolescents. With 1,836 participants enrolled, half received the BCG vaccine while the other half was given a placebo.

The results are surprising: after 30 months, both groups showed similar rates of sustained QFT test conversions, signaling potential tuberculosis infection—62 in the BCG group versus 59 in the placebo group. This translates to a hazard ratio of 1.04, which indicates no significant protective effect from the revaccination.

Adverse Effects and Immunological Responses

While the BCG group experienced more adverse events, mainly injection-site reactions, the study did register an increase in cytokine-positive type 1 helper CD4 T cells in participants who received the BCG vaccine. However, this immune response did not translate into effective protection against infection.

Implications and Future Directions

The authors conclude that the absence of efficacy in preventing infection casts doubt on the belief that BCG revaccination could guard against the development of tuberculosis disease. As the fight against tuberculosis continues amidst rising resistance and new infection cases, these findings underscore the urgent need for more effective vaccine strategies.