Most outbreaks have occurred in Africa, far from the Siberian lab where the senior technician was experimenting on guinea pigs when the accident happened on May 5. She died two weeks later.

Set deep in Siberia, a four-hour flight from Moscow, the state-owned Vector research center at Novosibirsk does research into deadly diseases such as SARS and anthrax.

Along with the U.S. Centers for Disease Control, it is one of only two places on earth with official stockpiles of smallpox, which killed around 300 million people last century.

After the accident, the woman was hospitalized in a ward specially equipped to contain virulent diseases. Anyone who came into contact with her was put under observation for three weeks.