The CDC says vials labeled ‘smallpox’ were found at a vaccine research facility in Pennsylvania

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

“Frozen vials labeled ‘Smallpox’ were accidentally discovered by a lab worker while cleaning out a refrigerator in a Pennsylvania vaccine research facility. CDC, Management partners and Law enforcement is investigating the matter and the contents of the vials appear to be intact,” the CDC added.

“Laboratory staff discovered the vials wearing gloves and masks. We will provide more details as they become available.”

Smallpox, also known as smallpox, was declared eradicated by the World Health Organization in 1980 following a concerted global vaccination effort. Before that, the virus, which can be easily transmitted 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.

In 2014, staff of the National Institutes of Health found six vials of smallpox in an unused storage room as they cleaned up the lab at NIH’s Bethesda, Maryland, campus to move it. Two of the vials contained surviving virus. The CDC said at the time there was no evidence that anyone had been exposed to the contents of any of the vials.

Governments have debated whether to keep virus samples or destroy all known copies. Most routine vaccinations were discontinued in 1972, but service members and some researchers are still vaccinated.

CDC suggestion that people get vaccinated against smallpox every 3-5 years to be protected although at least one study has shown that vaccinated people may have at least some immunity for life.