BCG Immunization: Efficacy, Limitations, and Future Needs

The bacille Calmette–Guerin (BCG) vaccine is one of the oldest and most widely used vaccines. The demonstration of its protective efficacy against tuberculosis (TB) in historical British Medical Research Council trials led to routine BCG vaccination in many parts of the world. Today, BCG vaccination policies vary across countries. BCG given once only at birth is the vaccination schedule currently practiced in most countries. In response to declining TB incidence rates, a number of countries have shifted from universal to selective BCG vaccination. Many countries have stopped BCG revaccination as evidence accumulates over its failure to confer additional protection. BCG vaccination of the HIV-infected is contraindicated, although neonatal BCG vaccination in TB-endemic countries may be continued until vaccination in HIV-exposed infants can be selectively deferred. Although BCG has demonstrated substantial protection against serious forms of TB, its protective effect against pulmonary TB is partial and variable. Without better vaccines and improved diagnostic and treatment tools, it may be difficult to meet the TB-related Millennium Development Goals. Concerted efforts are required to integrate scientific advancement and political mobilization in vaccine development, clinical trials, and field implementation.