A Merck lab worker in Pennsylvania found five vials labeled "smallpox" in a lab freezer, according to a Nov. 18 New York Times report. The worker was masked and gloved.
The CDC said in a statement that lab testing showed that the vials contained vaccinia, which is similar to the smallpox virus and was used to inoculate against the eradicated disease, according to a Nov. 18 NBC News report.
They did not contain the variola virus, which causes smallpox, the agency said.
"There is no indication that anyone has been exposed to the small number of frozen vials," CDC spokesperson Belsie Gonzalez said in an email to The New York Times.
Mark O'Neill, press secretary for the Pennsylvania Department of Health, said that "there has been no known threat to public health and safety," according to the report.