Several vials labelled "smallpox" have been found at a vaccine research facility in Pennsylvania, the U.S. 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 labelled '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 U.S. was in 1947.
In 2014, employees of the National Institutes of Health found six vials of smallpox in an unused storage room as they packed up a lab at the NIH's Bethesda, Maryland, campus to move it. Two of the vials contained viable virus. The CDC said at the time there was no evidence anyone had been exposed to the contents of any of the vials.
Governments have argued about whether to keep samples of the virus or to destroy all known copies. Most routine vaccination stopped in 1972 but military personnel and some researchers are still vaccinated. The CDC recommends that people who need long-term protection get smallpox boosters every 3-5 years, although at least one study indicated vaccinated people may have at least some immunity for life.
