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. 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.