Role of BCG vaccine in the present era: Old is gold or revisits its importance for TB elimination

The Bacillus Calmette-Guérin (BCG) vaccine has been a cornerstone of tuberculosis (TB) prevention for over a century. The BCG vaccine is most effective in newborns and infants, providing 60–80% protection against severe TB forms, such as miliary TB and TB meningitis. This protection lasts for 10–15 years. In children and adolescents, it continues to offer moderate protection against TB infection but becomes less effective against pulmonary TB. In adults, BCG has limited effectiveness against pulmonary TB, with protection varying by region. In the elderly, the vaccine’s protective effects wane significantly, and revaccination is not recommended previously. Beyond TB, emerging evidence suggests that BCG vaccination may offer broader immunological benefits, including protection against other infectious diseases and potential applications in cancer immunotherapy. Studies suggest that it may help against leprosy and some non-TB mycobacterial infections. The reintroduction of the BCG vaccine in the adult vaccination program revisits its definite role in preventing adulthood new tuberculosis infection and the reactivation of tuberculosis. It plays a critical role in public health campaigns, particularly in low- and middle-income countries where TB remains endemic. Effectiveness varies geographically, being higher in low-burden TB countries. This review explores the historical development, mechanism of action, effectiveness, and broader implications of the BCG vaccine in global health efforts.