Six vials of freeze-dried smallpox virus have been found tucked away in a Food and Drug Administration (FDA) cold storage room. The vials appear to have been stored there since the 1950s.

If there is anything thing more frightening than finding vials of an infectious disease that killed more than a billion people before being wiped out, it may be the fact that ten other vials were in the same box with unreadable labels.

Smallpox has a unique place in medical history. It is thought that no other virus, nor any bacteria, has killed as many people as Variaola major. Mortality rates for those infected are estimated at 30-35%

Variola minor, a slightly less virulent form of smallpox, only killed 1% of those infected, still enough to make it far more deadly than many diseases that cause alarm today. Even the survivors were usually left scarred, often on their cornea resulting in blindness.

Given the choice, one might still prefer to get smallpox than, for example, ebola. However, until 40 years ago the chance of getting smallpox was also much, much higher. It is estimated that in the 20th Century alone 300-500 million people died from the disease, a figure far higher than from war. It's eradication, through vaccination, was arguably the greatest triumph in medical history. Smallpox was the first infectious disease declared entirely eradicated, and in the 25 years since only rinderpest has followed.

Consequently, one of the great nightmares of public health officials has been the possibility of a revived smallpox outbreak. Whether it be through terrorist release or accident, the possibility that a the virus could somehow get back into circulation remains a concern. The smallpox's eradication vaccination has now ceased, so billions of people lack defenses if the disease were to return. Getting protection to the public before the disease would be a race worthy of a blockbuster film, even without the interference from anti-vaccination activists.

The vials were found on July 1 on the National Institutes of Health (NIH) Campus in Bethesda, Maryland. The storage room was initially part of an NIH laboratory, transferred to the FDA in the 1970s. The vials have been flown to the Centers for Disease Control and Prevention biosafety lab in Atlanta where they will be tested to see if the virus can be cultured, and then destroyed.

When smallpox was eradicated in 1979 stocks were maintained in Atlanta and Novosibirsk, Russia, for research purposes, and to produce vaccines should the disease return from some unknown repository. The find serves as a reminder that other forgotten samples may exist in inadequately protected locations.

“There is no evidence that any of the vials labeled variola has been breached, and onsite biosafety personnel have not identified any infectious exposure risk to lab workers or the public,” the CDC noted in their press release.