The Centers for Disease Control and Prevention is now running tests on the six forgotten vials of smallpox that were recently discovered in an unsecured laboratory, to see if any live virus remains in them.
The sealed vials were found in a lab at the National Institutes of Health (NIH) in Bethesda, Maryland, and had apparently been languishing there since the 1950s.
But the discovery is not a risk to the public, and even if live smallpox virus were accidentally released in a lab, it would be unlikely to spread disease in the general population, experts say.
"There's no reason for the general public to panic at this discovery," said Dr. Amesh Adalja, an infectious disease specialist and a senior associate at the University of Pittsburgh Medical Center's Center for Health Security. "There's no risk to the public of smallpox." [7 Devastating Infectious Diseases]
Smallpox is a disease caused by the Variola virus, and is related to several other poxviruses, including cowpox and monkey pox. The virus can spread from one person to another through the air, in respiratory droplets. It causes flulike symptoms, along with characteristic white blisters all over the body. About 30 percent of people who get sick with smallpox go into the serious state of reduced blood flow called shock, and die, Adalja said.
Smallpox has been around since the dawn of recorded history; there are even Egyptian mummies with pockmarked faces, Adalja said.
"It was a big scourge of the human race until it was eradicated from the planet in 1980," Adalja told Live Science.
The first vaccine against smallpox was developed in the 1700s, when biologist Edward Jenner noticed that women who milked cows were immune to smallpox after they had been infected with the much milder disease of cowpox, or vaccinia. So in 1796, Jenner inoculated people using pus from those infected with the cowpox virus, creating the world's first vaccine.
For hundreds of years, the live vaccinia vaccine was grown in cow skins, then in tissue cultures in the lab, but such vaccines caused complications. Scientists have since developed a third-generation vaccine that uses live-but-weakened virus, and doesn't have those side effects, said Grant McFadden, a virologist at the University of Florida who studies poxviruses.
Thanks to a worldwide effort to wipe out the disease, smallpox was declared officially eradicated in 1980, after the last natural occurrence of the disease happened in Somalia in 1977, and the last death from the disease occurred due to a laboratory accident in England in 1978, according to the World Health Organization.