There is no evidence that any of the vials was breached, and no lab workers or members of the public were exposed to the infectious and potentially deadly virus, the federal
The vials labeled variola — a name for the smallpox virus — were found July 1 "in an unused portion of a storage room" and seem to date to the 1950s, the CDC said. They were freeze-dried, intact and sealed, forgotten and packed away in a cardboard box, officials said.
The vials were "immediately secured" in a containment lab, then transported via government aircraft Monday to the CDC's containment facility in Atlanta, it said.
The samples are being tested to see whether any of them are viable – that is, can grow – and will then be destroyed, the CDC said.
No documentation was found to explain how or why the virus was left in the Maryland facility, though it appears the vials might have been retained inadvertently when the laboratories were transferred to the
Dr. Michael Osterholm, a biosecurity expert, said the samples didn't pose much of a threat as they sat for decades in a government storage room.
"Some vials in a freezer by themselves aren't going to pose a huge risk," said Osterholm, who is director of University of Minnesota's Center for Infectious Disease Research and Policy.
Officials say this is the first time unaccounted-for smallpox was discovered, but Osterholm said it shouldn't come as a shock.
"We have freezers like this in the world," he said. "The likelihood of finding more smallpox virus is real."
NIH workers also found 10 other vials labeled with unidentified contents. Only the six marked "variola" tested positive for smallpox DNA.
The most common type of smallpox is serious, contagious and frequently fatal, with about 30% of cases resulting in death, according to the CDC. Luckily, the disease was declared eradicated in 1980 after a worldwide vaccination program.
The last U.S. case of smallpox was in 1949, and the last naturally occurring case anywhere in the world was in Somalia in 1977, according to the CDC. Since then, according to the World Health Organization, the only known cases stemmed from a 1978 lab accident in England.
Only two labs – one at the CDC in Atlanta and another near Novosibirsk, Russia – are "designated repositories" for smallpox. All other labs in the world were required to destroy their smallpox strains or transfer them to the two laboratories, according to an international agreement reached in 1979.
A debate has been taking place in recent years over whether (or when) to destroy the last living strains of the virus. Some argue that the disease could reemerge, so virus samples are needed to conduct research that would protect the public. Others argue that keeping live samples is the very thing ensuring smallpox is not fully wiped out.
The World Health Organization decided in May to postpone a decision on whether to destroy remaining stocks.