A bottle of smallpox vaccine held by gloved fingers.

Several vials labeled “smallpox” have been found at a vaccine research facility in Pennsylvania, the US Centers for Disease Control and Prevention said Tuesday.

“There is no indication that anyone has been exposed to the small number of frozen vials,” the CDC said in a statement emailed to CNN.

“The frozen vials labeled ‘Smallpox’ were incidentally discovered by a laboratory worker while cleaning out a freezer in a facility that conducts vaccine research in Pennsylvania. CDC, its Administration partners, and law enforcement are investigating the matter and the vials’ contents appear intact,” the CDC added.

“The laboratory worker who discovered the vials was wearing gloves and a face mask. We will provide further details as they are available.”

Smallpox, also known as variola, was declared eradicated in 1980 by the World Health Organization after a concerted global vaccination effort. Before that, the virus, which passes easily from person to person, infected 15 million people a year and killed about 30% of them. The last known outbreak in the US was in 1947.

Read more….