A German researcher who accidentally exposed herself to the dreaded Ebola virus is apparently in the clear: the virus's three-week incubation period expired yesterday, her supervisor tells ScientificAmerican.com.

On March 12, a 45-year-old virologist (whose name was not released) at the Bernhard Nocht Institute for Tropical Medicine in Hamburg, Germany, accidentally jabbed herself with a syringe containing the virus that causes Ebola hemorrhagic fever, which kills up to 90 percent of its victims. It's symptoms: fever, body aches, diarrhea, vomiting, red eyes, and internal and external bleeding.

The slip occurred while the researcher, who had been studying new tests for Ebola infection, was injecting mice with the virus, according Stephan Günther, head of the institute's virology department. After reporting the incident to the institute, the woman rushed to the hospital, where she was placed in an isolated room and visited by doctors and nurses wearing protective gowns, gloves and masks.

That evening, Günther and his colleagues got on the phone with scientists from the U.S. and Canada, and together they decided to offer the woman an experimental Ebola vaccine that had never been tried in humans but which had shown promising results in monkeys -- even after they had been infected, Günther explains. Within 48 hours of the initial needle prick, researchers at Winnipeg's National Microbiology Lab in Canada had shipped the vaccine to Germany and it had been given to the woman.

About 14 hours later, she came down with a fever.

"At that moment, when she developed the fever, it wasn't clear if it was due to the Ebola virus," or to the vaccine, Günther says. But now that the virus' three-week incubation period has passed and no other Ebola symptoms have surfaced, Günther believes the vaccine—not the Ebola virus—was responsible.

"We are very confident the game is over," he says, noting that the woman was released from the hospital yesterday and is physically and psychologically stable. But how the woman evaded the disease remains a mystery – either she never became infected in the first place or the vaccine worked, Günther says. The good news, he says, "[is that] there were no serious side effects associated with the vaccine."

This is not the first time researchers have accidentally pricked themselves with needles containing the deadly Ebola virus. In 2004 a scientist from the U.S. Army Medical Research Institute of Infectious Diseases in Frederick, Md., poked himself when a kicking mouse caused his hand to slip. Fortunately, he never developed the disease.

Image of Ebola virions: Public Library of Science via Wikimedia Commons