Alert after smallpox samples found in US laboratory storeroom

US federal investigators are probing how vials of smallpox made their way into a storage room at a Food and Drug Administration lab near the US capital, health authorities said.

Smallpox is a highly contagious and sometimes fatal disease that is estimated to have killed some 300 million people in the 20th century alone.

Though there is no treatment for smallpox, it has been eradicated after a worldwide vaccination programme. The last US case was in 1949; the last global case was in 1977 in Somalia.

The vials were labelled "variola", another name for smallpox, and appeared to date from the 1950s, the US Centres for Disease Control and Prevention said.

They were found in an unused portion of a storeroom in an FDA laboratory, located on the National Institutes of Health campus in Maryland.

There was no evidence that the vials had been opened, and "onsite biosafety personnel have not identified any infectious exposure risk to lab workers or the public", the CDC said. The vials have been moved to a high-security lab at the CDC headquarters in Atlanta.