PHILADELPHIA, Pa. — Frozen vials labeled “smallpox” that were recently discovered at a Pennsylvania facility contained no trace of the virus that causes the eradicated disease, according to the Centers for Disease Control and Prevention (CDC).
The public health agency said in a statement Thursday evening that laboratory tests showed that the vials actually contained vaccinia, the virus used in smallpox vaccines.
“CDC is in close contact with state and local health officials, law enforcement, and the World Health Organization about these findings,” wrote the CDC.
The U.S. government was notified on Monday that the small number of intact, frozen vials labeled “smallpox” were discovered by a laboratory worker while cleaning out a freezer in a facility that conducts vaccine research.
Officials say the facility was immediately secured and staff followed protocols for notifying the CDC of such a potential discovery. The vials were sent to the CDC for testing on Wednesday to determine what they contained, and officials say no one was exposed to contents.
The World Health Organization (WHO) declared smallpox eradicated in 1980 after a global vaccination effort that was launched in 1967. The last known natural case of the acute contagious disease was in Somalia in 1977, according to the WHO.
The WHO calls smallpox “one of the most devastating diseases known to humanity,” having caused millions of deaths before it was eradicated. It’s believed to have existed for at least 3,000 years.
Samples of smallpox still exist, but the WHO has designated only two sites for smallpox storage. One is at the CDC in Atlanta, and another is in Russia.