What is the only disease totally eradicated from earth?

• A. Polio
• B. Smallpox
• C. Diphtheria
• D. Measles

Answer: (B)

Eradication means no cases anywhere in the world and the disease can no longer spread. Smallpox achieved this because it only infects humans (no animal reservoir), presents in a distinctive way that makes cases easy to identify, and there is a highly effective vaccine that confers long-lasting immunity. Combined with intensive global surveillance and rapid vaccination of contacts (ring vaccination), transmission was interrupted everywhere and new cases stopped. In 1980 the WHO declared smallpox eradicated.

Polio still occurs in some regions because transmission can be hidden in people who don’t show symptoms, and keeping vaccination coverage so high everywhere is challenging; measles remains endemic in places with gaps in vaccination and its very high contagiousness allows outbreaks when immunity slips; diphtheria outbreaks can still happen where vaccination rates are low.