The vials marked ‘Smallpox’ that were found at the Merck laboratory in Upper Gwynedd Township last week did not contain the deadly virus after all, according to the Centers for Disease Control and Prevention, writes Johnny Diaz for The New York Times.

The vials “were incidentally discovered by a laboratory worker while cleaning out a freezer in a facility that conducts vaccine research in Pennsylvania,” said Belsie González, a spokeswoman for the CDC.

According to Kelly Cofrancisco, a spokeswoman for the Montgomery County Office of Communications, there were “15 questionable vials” found, with five of them labeled “smallpox” and 10 as “vaccinia.”

After running laboratory tests, the CDC found that instead of the variola virus, which causes the disease, the five vials also contained vaccinia, the virus that is used in the smallpox vaccine.

The CDC conducted the investigation while remaining in close contact with state and local officials, law enforcement, and the World Health Organization.

“The Pennsylvania Department of Health would like to stress that there has been no known threat to public health and safety,” said Mark O’Neill, a press secretary for the department.

Read more about the vials in The New York Times.