Effect of Bacillus Calmette-Guérin vaccination against Mycobacterium tuberculosis infection in children: an updated systematic review and meta-analysis.

Objective: To update the understanding of the effectiveness of the Bacillus Calmette-Guérin (BCG) vaccine in preventing tuberculosis (TB) infection in children.

Methods: PubMed, Web of Science, Cochrane, and Embase were searched from their inception to January 12, 2025. Studies were included if they focused on children under 19 years exposed to pulmonary TB, used interferon-gamma release assays (IGRA) for infection assessment, and reported IGRA-positive outcomes for both BCG and non-BCG groups. Pooled estimates were derived using random-effects meta-analysis, with heterogeneity assessed by the I² statistic.

Results: Total 8242 participants were enrolled in 32 studies. The overall protective effectiveness of BCG against infection was 18%, with a relative risk [RR] of 0.82 (95% confidence interval [CI]: 0.73-0.91], I² = 60%). Subgroup analysis revealed a higher effectiveness of 29% (RR = 0.71 [95% CI: 0.62-0.82], I² = 41%) in low-TB incidence areas, while effectiveness was not significant (RR = 0.95 [95% CI: 0.84-1.09], I² = 55%) in high-TB incidence areas.

Conclusions: BCG vaccination shows protective effectiveness against TB infection, particularly in low-TB incidence areas. Its effectiveness in high-TB incidence areas remains uncertain, underscoring the need for further research to optimize vaccination strategies in these settings.