At one time, smallpox was one of the most dangerous diseases on Earth. Worldwide, an estimated 300 million people died of smallpox in the 20th century.

But after global vaccination efforts in 1979, the World Health Organization declared smallpox to be eradicated. The last known case of smallpox was reported in 1977.

Live samples of the virus still exist, however, stored in highly-secure labs in the US and Russia. World health experts are scheduled to meet this week to discuss, once again, whether or not it's time to destroy these samples and remove them from the earth.

Not everybody thinks destroying the virus is the best idea. Inger Damon, head of the Poxvirus and Rabies Branch at the Centers for Disease Control and Prevention, argues that the time is not yet right to destroy the last live samples.

“There is more work to be done before the international community can be confident that it possesses sufficient protection against any future smallpox threats,” Damon and her colleagues wrote in a recent editorial.

After eradication was declared, Damon says, samples of the virus were collected and stored by the World Health Organization for the purpose of conducting additional research on it. DNA sequencing and some initial anti-viral screening were done in the 1990s, and in the 2000s the research agenda was “ramped up” even more, Damon says.

“We really wanted to look at applied research,” Damon explains, “which could help us develop diagnostics to detect the disease, antivirals to treat disease, and less reactogenic vaccines to prevent disease. The work that we've been doing over the past fifteen years has been designed to make our country, and all countries, more prepared if smallpox does re-emerge.”

The re-emergence of the virus is a risk that has been raised by some of the same people involved in the eradication programs, notably D.A. Henderson, who led the efforts beginning in the 1960s. Nonetheless, Henderson now says he supports destroying the remaining samples of the virus.

“When the materials were consolidated into the two repositories — one in the United States and the one in Russia — there was no concerted effort at that time to verify that all materials had, in fact, been collected,” Damon says. “So there's some uncertainty about what might exist in some of these older freezers in laboratories where diagnostics had been done for smallpox.”

After the attacks of 9/11, and the anthrax scare that followed, fear grew that bio-terrorists could be hoarding samples of smallpox and might use it as a weapon of biological warfare. Smallpox would be an effective bio-terror weapon: it spreads rapidly and kills about one-third of those it infects. If we no longer have our own samples of the virus, Damon says, our ability to respond to it could be dangerously slowed.

“Currently less than 50 percent of [the global] population has ever been vaccinated for this virus,” she adds. “We’re [also] seeing an increased incidence of other, related poxvirus infections — likely because of the cessation of routine vaccination in 1980, when the eradication of smallpox was declared.”

Scientists in favor of destroying the virus say the chances of a new smallpox outbreak are miniscule. Even if this were to happen, they say advances in synthetic biology have given us the ability to rebuild the virus from scratch in an emergency.

But Damon thinks that is an even more frightening idea.

“I think that sets a precedent that we really don’t want to entertain,” she says. “It’s better to use the remaining materials we have wisely.” Live samples of the virus have been used to test new antiviral drugs, for example, and more work is being done in this direction, Damon says.

But she and other scientists feel they have not yet achieved their goals. For example, she says, they would like to develop licensed products which are easy to use.

“Right now,” she says, “we have investigational products, which certainly can be used and have been used. But the ability to use them quickly in a response is more cumbersome under that investigational use. If you've gone through the full licensure status, and regulatory groups have reviewed a treatment, they’ve already ... put their stamp of approval on it — in effect saying, ‘This treatment meets the standards under which this material can be safely used.’"

Damon says she is confident her view will prevail at the upcoming meetings.

This story is based on an interview by our partner Science Friday, a weekly radio show and website covering science, technology and other cool stuff.