The Centers for Disease Control and Prevention is looking into the discovery of smallpox-like substances at a laboratory in Pennsylvania.
Belsie Gonzlez, a spokeswoman for the C.D.C., said in an email that the frozen vials were discovered by a laboratory worker while cleaning out a freezer in a facility that conducts vaccine research in Pennsylvania.
She said that the C.D.C. was working with law enforcement to investigate. The agency said the vials were intact.
She said that the laboratory worker who discovered the vials was wearing gloves and a face mask. There is no indication that anyone has been exposed to the small number of frozen vials. We will give further details when they are available.
The C.D.C. didn't say where the vials were found or how many there were.
A small number of pills were found at a facility in Montgomery County, outside Philadelphia, according to Mark O'Neill, a press secretary for the Pennsylvania Department of Health.
The company did not respond to the request for comment on Thursday. The C.D.C was referred to by the Federal Bureau of Investigation.
There has been no known threat to public health and safety, according to the Pennsylvania Department of Health. There is no indication that anyone was exposed to the small number of frozen vials that were labeled smallpox.
According to the C.D.C., smallpox caused devastating outbreaks for centuries, with about three of every 10 cases proving fatal.
There is a progressive skin rash and a very high temperature.
The World Health Organization says the virus killed 300 million people in the 20th century.
The C.D.C. said that there is enough vaccine for everyone in the United States.
The last natural outbreak of the disease in the US was in 1949. The last natural case was in 1977.
The C.D.C. in Atlanta and a research center in Russia are authorized to hold variola virus stocks, according to the W.H.O. Six glass vials of the smallpox virus were found in a storeroom in a government laboratory outside Washington. The C.D.C. said there was no indication that lab workers or the public had been exposed to the contents.
The C.D.C. said that the development of vaccines, drugs and diagnostic tests to protect people against smallpox was the focus of research in the United States.
Even after it is freeze-dried, smallpox can be lethal, according to an emergency physician at a New York hospital.
He said that because of its infectious nature, the virus must be kept cold. He said that it was unlikely that the virus would retain its ability to spread.
There was a debate about whether governments should retain viral samples or eliminate all known copies of the virus.
