Epidemiological basis of small pox eradication

Small pox which was once a killer disease wreaking havoc around the world was declared eradicated by the WHO on 8th May 1980. The following factors helped in eradicating small pox.

1. Small pox has no known animal reservoir
2. There is no long term carrier state
3. Infection produces lifelong immunity
4. Subclinical infections are not communicable
5. The disease was easily identified by its characteristic rash
6. The vaccine was effective and heat stable
7. There was international cooperation in eradicating small pox