"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," the CDC added. "CDC, its Administration partners, and law enforcement are investigating the matter and the vials' contents appear intact. "The laboratory worker who discovered the vials was wearing gloves and a face mask. We will provide further details as they are available."
ALSO READ | New Jersey mom admitted planning deaths of young daughter, son: Investigators
According to Yahoo News, which cited an alert sent to Department of Homeland Security leadership, the vials were reportedly found in a freezer Monday night at a Merck facility outside Philadelphia.
The closest Merck sites to Philadelphia are the sprawling campuses in West Point and North Wales, Montgomery County, although sister station Action News in Philadelphia cannot confirm there are questionable vials inside the building.
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.
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.
ALSO READ | Vaccinated families can 'feel good' about gathering for holidays, Fauci says
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 get smallpox boosters every 3-5 years to stay protected, although at least one study indicated vaccinated people may have at least some immunity for life.
The-CNN-Wire & 2021 Cable News Network, Inc., a WarnerMedia Company contributed to this report.
* Get Eyewitness News Delivered
* Follow us on YouTube
* More local news
* Send us a news tip
* Download the abc7NY app for breaking news alerts Submit a News Tip