BCG Tuberculosis Vaccine — Calmette and Guérin (1921)

The BCG tuberculosis vaccine, developed by Calmette and Guérin in 1921, is the most widely administered vaccine in history with over 4 billion doses given, yet it remains essential for preventing severe childhood TB in endemic regions. Despite variable efficacy against adult pulmonary TB, it reduces the risk of meningeal tuberculosis by 60% in children, outpacing the yellow fever vaccine (#8) in terms of total lives saved due to its broader distribution. Its durability is evidenced by a protection period of up to 15 years after a single dose, making it a cornerstone of global TB control programs. The vaccine costs less than $1 per dose, ensuring accessibility in low-resource settings.