FBI, CDC investigating several vials labeled 'smallpox' found at vaccine research facility

Several vials labeled as "smallpox" that were discovered at a Merck & Co. vaccine research facility near Philadelphia did not contain the virus that causes smallpox, the Centers for Disease Control and Prevention said in a statement Thursday.

According to the unclassified "For Official Use Only" alert – obtained by several media outlets – sent by the Department of Homeland Security, there were a total of 15 "questionable vials," five of which were labeled as “smallpox” while the other 10 were labeled as "vaccinia." The vials were immediately secured upon discovery.

"There is no indication that anyone has been exposed to the small number of frozen vials," the CDC said in a statement. "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 and the FBI opened investigations, according to the Department of Homeland Security.

The vials were later found to contain vaccinia, the virus used in the smallpox vaccine, but did not contain the variola virus that causes smallpox, according to a statement obtained by USA TODAY from the the Centers for Disease Control and Prevention

Fact check: Vaccination helped eradicate smallpox

Smallpox, a deadly and contagious virus, was declared eradicated in 1980 by the World Health Organization after a concerted global vaccination effort. The virus had infected 15 million people a year and killed about 30% of them, with the last known outbreak in the U.S. in 1947.

According to Live Science, only two labs in the world are authorized to store samples, including one in Russia and the other at the CDC in Atlanta. The facility in Russia had a scary explosion in 2019, but no outbreaks came as a result. It is unclear how potential samples were allowed in the Philadelphia Merck facility.

Scientists have long debated whether to destroy any remaining samples, with some arguing against the danger because the samples could be needed to develop new vaccines in response to a new outbreak.

A majority of Americans are not vaccinated against smallpox, according to the CDC.

According to the Mayo Clinic, there is no treatment or cure for smallpox. A vaccine can prevent it, however, the vaccine's side effect risk is too high to justify routine vaccination.

This article originally appeared on USA TODAY: Vials labeled as smallpox found in Philadelphia facility