CDC finds no smallpox in frozen vials suspected of being labeled ‘Smallpox’

Vial with smallpox vaccine sitting on a disc before a vaccination December 16, 2002 at Mid-Florida Biologicals in Altamonte Springs, Florida

Vial with smallpox vaccine sitting on a disc before a vaccination December 16, 2002 at Mid-Florida Biologicals in Altamonte Springs, Florida
Photo: Chris Livingston (Getty Images)

Days after a laboratory in Pennsylvania was locked down because a worker discovered vials labeled “smallpox” in a freezer, the CDC says there is no reason to fear a viral outbreak. Late Thursday night, federal officials announced that the vials did not contain the deadly and eradicated variola virus. Instead, they kept a related but much tamer virus, one used to make smallpox vaccines.

Earlier this week, the Centers for Disease Control and Prevention revealed that a lab employee had uncovered the frozen vials as they cleaned a freezer at a Pennsylvania-based Merck vaccine research facility working with the CDC. There were 15 vials in total, five of which were labeled “smallpox” and a further 10 labeled “vaccinia”. It writes the New York Times, referring to a local official. The vials were then transferred elsewhere for testing on Wednesday. And it now turns out that the “smallpox” vials also contained vaccinia virus.

“There is no evidence that the vials contain the variola virus, the cause of smallpox,” the CDC said in a statement sent Thursday to the New York Times.

Vaccinia is a virus with one exciting backstory. Edward Jenner developed the first smallpox vaccines in the late 18th century using what he thought were smallpox, a cousin of smallpox that causes less serious disease in humans (smallpox killed 30% or more of its victims). However, whether the original inoculations actually contained smallpox is not clear, as the virus used in the vaccines that became the basis of mass vaccination programs ended up being vaccinia, which is very similar to smallpox. The discrepancy was not detected for a long time, and no one is sure whether vaccinia evolved from the first laboratory-grown cowpox strains, from another related virus called horse cups, or as a hybrid of multiple smallpox viruses. Its true origin is still a mystery, and vaccinia is not thought to exist in nature. When it was confirmed to be a really distinct virus, vaccinia was named after the technology it was known for.

At least vaccination with vaccinia much less harmful than actually getting smallpox, although the shot can often jumpafe behind a characteristic hudar at the injection site. The chances of someone being exposed to the contents of the freezers were low, the CDC said, as they were left intact at the time of the discovery and the lab worker was reportedly wearing a face mask and gloves at the time.

Just over five years ago, laboratory workers from the National Institutes of Health did run into such a cache of smallpox samples, some of which contained viable viruses. And while there are only two sanctioned sites in the U.S. and Russia where smallpox can be stored for examination, scientists suspect there are a few hidden stocks elsewhere. For now, however, there is no immediate risk of a smallpox successor.

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