A scenario ripe for a zombie-horror movie has just happened. The U.S. Centers for Disease Control and Prevention revealed Tuesday that vials labeled “smallpox”—an extremely deadly virus that was eradicated in the 1970s—were found at a vaccine research facility in Pennsylvania. Despite the scary find, officials say there is no evidence that anyone’s been exposed to the pathogen.
According to the CDC, the frozen vials were found by a lab worker as they were cleaning out a freezer. The vials don’t appear to have been opened, and the worker was wearing gloves and a face mask at the time of the discovery. The facility is one of many that conduct vaccine research for the CDC.
“There is no indication that anyone has been exposed to the small number of frozen vials,” the CDC said in a statement to CNN. “CDC, its Administration partners, and law enforcement are investigating the matter and the vials’ contents appear intact.”
The CDC will transport the vials to another location for testing on Wednesday, Yahoo News reported, citing an alert sent to Department of Homeland Security leadership. According to the DHS alert seen by Yahoo News, there were 15 vials; five were labeled “smallpox” and 10 were labeled “vaccinia.”
Smallpox, named for the characteristic pockmarks it causes on the skin, is one of the more fearsome germs that has plagued humanity. It’s been responsible for countless epidemics and is estimated to have killed 300 million people in the 20th century alone. However, the virus was also the first to be beaten back through vaccination, when the technique of inoculation was improved and popularized by Edward Jenner in the late 18th century. The disease was finally eradicated worldwide in 1977, a feat aided by the fact that humans are the only known natural host of smallpox.
Though smallpox is (probably) gone from the wild, there do remain legally allowed samples of the virus at select labs in the U.S. and Russia—a decision that’s earned a fair share of controversy. In recent years, there have been discoveries of undocumented smallpox, such as when workers at the National Institutes of Health found six vials preserved from the 1950s during a move. Two of these vials were later shown to contain viable virus, though no cases of smallpox occurred as a result.
As scary as an accidental release of smallpox would be, there are smallpox vaccines available, though they’re only given to people who could be at risk of exposure, such as certain lab workers. Today, Americans are no longer routinely vaccinated against smallpox. In 2018, the Food and Drug approved the drug tecovirimat as the first antiviral specifically meant to treat smallpox, based on data from tests in the lab on smallpox and its cousins.
There are occasional cases of other related diseases in the U.S., such as monkeypox and Alaskapox, though none of these are as serious or prevalent as smallpox was in its heyday.