How do we know smallpox has been eradicated forever?

On the last point, the WHO may have been a bit premature in declaring smallpox eradicated in 1980 - smallpox can persist in the environment for years (it takes about 8 years for 99% of it to be inactivated in moderate conditions: Persistence of Category A Select Agents in the Environment). read more

On 26 July 1978, WHO announced the eradication of the smallpox strain Variola Minor. The more deadly strain, Variola Major, had been eradicated several years earlier, in 1975. There remains a stockpile of the virus in storage in 600 frozen vials in Atlanta and Russia. This has been deemed necessary, in case further vaccines are required in the future. read more

Vaccination with the vaccinia virus as a protection against smallpox is not recommended for widespread use. read more

Smallpox has existed for at least 3,000 years and was one of the world’s most feared diseases until it was eradicated by a collaborative global vaccination programme led by the World Health Organization. The last known natural case was in Somalia in 1977. read more

Smallpox has been eradicated from the globe, with no new cases reported since 1978. The threat of bioterrorism keeps the danger of smallpox alive, however, and debate continues over whether strains of the disease should be retained in specified laboratories. read more