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Mystery: Did Experimental Vaccine Save Ebola Accident Victim's Life?

7 April 2009 9:09 am
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A researcher who pricked herself with a needle containing the Ebola-Zaire virus last month is expected to come back to work at the Bernard Nocht Institute in Hamburg, Germany, after Easter. Scientists are now planning an extensive series of tests to determine her reaction to an experimental vaccine rushed in from Canada after the accident. But they may never know for sure whether the shots saved her life.

The researcher, whose name has not been made public, was released from a hospital on Thursday, says Stephan Günther, the head of the institute’s virology department. Hamburg health authorities allowed her to leave exactly 3 weeks after the start of the ordeal, corresponding to the maximum known incubation time for Ebola, pictured above courtesy of NIH.

Within 48 hours after the accident, the researcher was inoculated with an experimental vaccine against Ebola-Zaire, developed at Canada's National Microbiology Laboratory in Winnipeg but never tested in humans before. The vaccine is based on a livestock pathogen called vesicular stomatitis virus, which has been engineered to express a glycoprotein also present on Ebola's envelope.

The patient, her doctor, and other scientists called in to consult on the case had picked this particular candidate vaccine over several others because a similar vaccine against Marburg based on stomatitis, a close cousin of Ebola, offered protection even when given after exposure to the virus. They reasoned that the same would be true for the Ebola vaccine.

But whether the vaccine actually prevented an infection will be difficult to say, says Günther. One problem is that—unlike, say, in monkey studies, in which a fixed amount of virus is injected—it's unclear whether virus particles actually entered the researcher's body; they may not have left the needle during the mishap, for instance. In that case, there was nothing to protect against.

Antibody tests might normally reveal that the researcher was exposed to the virus, but standard tests look for antibodies against Ebola's glycoprotein, which is the same in the virus and the vaccine. That means that even if these antibodies are found, scientists can't be sure whether they were triggered by the virus itself or by the vaccine, says Boston University virologist Thomas Geisbert, who has tested the vaccine in monkeys at the U.S. Army Medical Research Institute of Infectious Diseases in Fort Detrick, Maryland.

The only way for researchers to conclude with certainty that the virus entered the researcher’s body would be finding an immune response that can only have been triggered by the virus itself—for instance, against Ebola's nuclear proteins or a so-called matrix protein called VP40. Detecting these antibodies is difficult, however; Günther says he will contact other labs specializing in Ebola to see whether they can help provide the assays.

If those telltale signals of exposure are found, however, they would strongly suggest that the vaccine saved the woman’s life, because injection seems to be a particularly lethal entry route for the virus, says Geisbert. In past experience, such as during the 1976 Ebola outbreak in Zaire, very few patients known to have been infected through needle accidents survived, he says.

Whatever route researchers take, they'll need to make sure to judiciously use blood collected after the accident, says Geisbert. "You don't want to burn through those precious samples with tests that aren't well-validated," he says. "The urgency is gone, we're left with academic questions now," adds Günther. "This is going to take some time."

The scientist is still on leave, recovering from the stress and anxiety of a brush with one of the most lethal viruses, says Günther. She has declined numerous interview requests, he says.

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