If smallpox were still around today, no one would have parties to infect their children, like they do with chickenpox. Smallpox was no joke. The disease used to infect 50 million people a year, and as many as one in three infected people died. Most survivors were scarred with pockmarks, and some were left blind.

Of course, no one gets smallpox today. It's the only infectious disease of humans that we've successfully eradicated. The World Health Organization (WHO) began a serious vaccination campaign against smallpox in 1967 (though vaccination had been possible since around 1800), and in just a decade the disease had been wiped out. The last naturally occurring case of smallpox struck in 1977. Then laboratories set out to destroy their remaining stocks of the virus. By 1984, smallpox had been erased from everywhere on Earth except for two labs--the Centers for Disease Control in the United States, and another site in Russia--that had been designated by the WHO as the disease's last refuges.

Now that we've consigned our longtime killer to custody, do we keep it indefinitely for observation? Or execute it?

The United States and Russia want to keep it for research. A contingent of mostly developing nations, led by Iran, wants the virus destroyed completely. These countries fear that in the event of an accidental--or deliberate--release, they would be most vulnerable. But American and Russian scientists say there's still more to be learned from keeping smallpox around, and that further research could help protect us if the disease somehow does return in the future.

Kathleen Sebelius, the U.S. secretary of health and human services, published an op-ed in the New York Times last month insisting that we should delay destroying our virus stocks. "We fully agree that these samples should--and eventually will--be destroyed," she said. "Although keeping the samples may carry a minuscule risk...the dangers of destroying them now are far greater." Sebelius was working against a deadline: a meeting of the World Health Assembly this month in Geneva, at which the fate of the virus would be reconsidered.

At the meeting, the United States and Russia asked to be allowed to keep the virus for five more years. They were met with strong opposition from the group of developing nations, though Canada, Australia, and the EU supported keeping the virus. Finally, a compromise (proposed by ever-neutral Switzerland) was reached: smallpox will survive for now, and the issue will be reconsidered in 2014.

It may seem foolhardy to hold on to such a deadly weapon. But there are many good reasons to keep smallpox around. Although vaccines exists, better vaccines could be created. Current vaccines can't be taken by individuals with HIV, for example. When smallpox was last prevalent, HIV didn't exist yet. But if smallpox were to reappear now, large numbers of people in Africa couldn't be vaccinated.

Additionally, there's no proof that these stocks of smallpox are really the last ones in the world. And as Sebelius points out, the virus's genome is freely available online. Someone with advanced equipment (or perhaps, in future years and as synthetic biology technology advances, average equipment) could hypothetically create the virus from scratch.

So destroying the American and Russian viruses wouldn't guarantee that the virus never reappears--only that we couldn't study it any further. The issue may have eerie echoes of a nuclear arms race, but this race is really between us and one of nature's worst weapons.