Story highlights Vials of smallpox virus that appear to date back to the 1950s found at NIH laboratory

Only two sites around the globe are allowed to hold the smallpox virus

The NIH has not identified any infectious exposure risk to lab workers or the public

You never know what you're going to find in an unused storage room. Employees at the National Institutes of Health, for example, recently discovered some old vials of variola.

You may know variola by its less formal name -- smallpox . Yes, the deadly virus that was the scourge of civilization for centuries. It's been considered an eradicated disease ever since 1980, following successful worldwide vaccination programs. The last known outbreak in the U.S. was in 1947 in New York.

The vials appear to date back to the 1950s, according to the Centers for Disease Control and Prevention, which released a statement on Tuesday about the discovery.

Scientists made the discovery when they were preparing to move a lab from the Food and Drug Administration's Bethesda, Maryland, campus to a different location. The laboratory had been used by the NIH but was transferred to the FDA in 1972. The vials were located in an unused part of a storeroom.

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When the scientists found the vials, they immediately put them in a containment lab and on July 1 notified the branch of the government that deals with toxic substances, called the Division of Select Agents and Toxins.

The CDC says there is no evidence that any of the vials was breached, nor were any of the lab workers exposed to the virus.

On Monday, law enforcement agencies transferred the vials to the CDC's high-containment facility in Atlanta. Testing confirmed that there was variola virus DNA in the vials. Scientists will do some more testing to see if it could grow in tissue culture. Once the tests are done, the CDC will destroy the samples.

The CDC is one of only two official World Health Organization designated repositories for smallpox. The other is in Novosibirsk, Russia. The CDC let the WHO know about the find and invited the WHO to witness the destruction of the vials, which is the standard protocol any time anyone finds smallpox samples unexpectedly.

The FBI is investigating how the samples ended up where they did.