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http://www.thecanadianpress.com/eng...me=x040506A&newsitemid=346697028&languageid=1
Ebola lab accident could reveal info about efficacy of experimental vaccine
Helen Branswell, THE CANADIAN PRESS
TORONTO - The makers of an experimental Ebola vaccine are hoping the blood of a German researcher exposed to Ebola virus will reveal whether use of the vaccine helped save her life.
No one in the close community of special pathogens researchers would have wished for the type of lab accident that led to the vaccine's emergency use last month.
But they hope to turn an unfortunate event into an opportunity. The unnamed woman, who has survived, was the first human to receive this experimental vaccine, made at the National Microbiology Laboratory in Winnipeg.
"I think we'll learn some more about this vaccine and how it behaves in humans, that's for sure," says Dr. Frank Plummer, scientific director of the Winnipeg lab.
Plummer and Dr. David Butler-Jones, Canada's chief public health officer, made the decision to let the woman's doctors inject her with the Winnipeg vaccine, the only one of several experimental Ebola vaccines which has been shown to enhance chances of survival after exposure to the deadly virus.
Whether the vaccine helped save the woman's life is unclear. In fact, it's not yet known if she became infected with Ebola virus when she pricked her finger with the needle of a syringe containing the virus.
The only real symptom she is said to have developed was a fever about 12 hours after she received the vaccine. That, experts say, was likely a response to the vaccine.
The scientist who led the effort to make the vaccine explains that at this point there are several possible options.
Testing the woman's blood for antibodies to the Ebola virus could reveal she was never infected, says Dr. Heinz Feldmann, who now heads the laboratory of virology at the U.S. National Institute of Allergy and Infectious Diseases' Rocky Mountain Laboratories in Hamilton, Mont.
If that's the case, the use of the vaccine will have shown it was safe in at least one person. Blood tests will also show whether the vaccine triggered an immune response in the woman. But that won't answer questions about whether the vaccine would protect her against infection with Ebola virus in the future.
If testing suggests she was infected, analysis of her blood might reveal antibodies to both the vaccine and the Ebola virus. That would suggest the vaccine halted the replication of the virus, in effect saving her life.
But Feldmann acknowledges there is another possibility: The woman may have been infected but hadn't yet started to develop antibodies to the virus when she was given the vaccine. In that case, the only antibodies that would be found would be to the vaccine.
In other words, the vaccine would have saved her life - but there would be no evidence on which to make the claim.
Feldmann believes, given the woman's lack of symptoms, that this may be the most likely scenario.
"That is my worry," he admits. "I hope they will prove me wrong but I am a little bit pessimistic at this point."
Either of those scenarios will leave many questions unanswered.
"If we get negative results, then we will never know whether she was infected or the vaccine reduced it to a level that the body did not respond to the infection," Feldmann says.
"So negative results will not give an answer. Positive results will give an answer."
Even figuring out whether she was infected won't be straightforward. The vaccine is made with a hybrid virus, one in which a protein from the Ebola virus is grafted onto a weakened but live vesticular stomatitis virus.
The hybrid awakens the immune system to the Ebola protein without causing infection, prompting it to generate antibodies against Ebola. So the trick will be to sift through the antibodies in the woman's blood looking for both ones that respond to the non-Ebola proteins in the vaccine, and for ones generated by the virus itself.
The mere act of giving the woman the vaccine will make it more difficult to learn whether she was even infected in the first place, admits Tom Geisbert, who tested the Winnipeg vaccine in monkeys at the U.S. Army Medical Research Institute of Infectious Diseases at Fort Detrick, Md.
"It's difficult to dissect out her response to the potential exposure with live wild-type Ebola virus versus the vaccine," says Geisbert, who is now associate director of the new National Emerging Infectious Diseases Laboratories Institute at Boston University.
"Not impossible, but more difficult. We've complicated it."
"But if it turns out that she really was exposed, if we find evidence of antibodies against ... an Ebola protein that we can absolutely say for certain she obviously saw (was exposed to) Ebola virus, then that clearly shows that the vaccine worked," he says.
http://www.thecanadianpress.com/eng...me=x040506A&newsitemid=346697028&languageid=1
© The Canadian Press , 2009
Ebola lab accident could reveal info about efficacy of experimental vaccine
Helen Branswell, THE CANADIAN PRESS
TORONTO - The makers of an experimental Ebola vaccine are hoping the blood of a German researcher exposed to Ebola virus will reveal whether use of the vaccine helped save her life.
No one in the close community of special pathogens researchers would have wished for the type of lab accident that led to the vaccine's emergency use last month.
But they hope to turn an unfortunate event into an opportunity. The unnamed woman, who has survived, was the first human to receive this experimental vaccine, made at the National Microbiology Laboratory in Winnipeg.
"I think we'll learn some more about this vaccine and how it behaves in humans, that's for sure," says Dr. Frank Plummer, scientific director of the Winnipeg lab.
Plummer and Dr. David Butler-Jones, Canada's chief public health officer, made the decision to let the woman's doctors inject her with the Winnipeg vaccine, the only one of several experimental Ebola vaccines which has been shown to enhance chances of survival after exposure to the deadly virus.
Whether the vaccine helped save the woman's life is unclear. In fact, it's not yet known if she became infected with Ebola virus when she pricked her finger with the needle of a syringe containing the virus.
The only real symptom she is said to have developed was a fever about 12 hours after she received the vaccine. That, experts say, was likely a response to the vaccine.
The scientist who led the effort to make the vaccine explains that at this point there are several possible options.
Testing the woman's blood for antibodies to the Ebola virus could reveal she was never infected, says Dr. Heinz Feldmann, who now heads the laboratory of virology at the U.S. National Institute of Allergy and Infectious Diseases' Rocky Mountain Laboratories in Hamilton, Mont.
If that's the case, the use of the vaccine will have shown it was safe in at least one person. Blood tests will also show whether the vaccine triggered an immune response in the woman. But that won't answer questions about whether the vaccine would protect her against infection with Ebola virus in the future.
If testing suggests she was infected, analysis of her blood might reveal antibodies to both the vaccine and the Ebola virus. That would suggest the vaccine halted the replication of the virus, in effect saving her life.
But Feldmann acknowledges there is another possibility: The woman may have been infected but hadn't yet started to develop antibodies to the virus when she was given the vaccine. In that case, the only antibodies that would be found would be to the vaccine.
In other words, the vaccine would have saved her life - but there would be no evidence on which to make the claim.
Feldmann believes, given the woman's lack of symptoms, that this may be the most likely scenario.
"That is my worry," he admits. "I hope they will prove me wrong but I am a little bit pessimistic at this point."
Either of those scenarios will leave many questions unanswered.
"If we get negative results, then we will never know whether she was infected or the vaccine reduced it to a level that the body did not respond to the infection," Feldmann says.
"So negative results will not give an answer. Positive results will give an answer."
Even figuring out whether she was infected won't be straightforward. The vaccine is made with a hybrid virus, one in which a protein from the Ebola virus is grafted onto a weakened but live vesticular stomatitis virus.
The hybrid awakens the immune system to the Ebola protein without causing infection, prompting it to generate antibodies against Ebola. So the trick will be to sift through the antibodies in the woman's blood looking for both ones that respond to the non-Ebola proteins in the vaccine, and for ones generated by the virus itself.
The mere act of giving the woman the vaccine will make it more difficult to learn whether she was even infected in the first place, admits Tom Geisbert, who tested the Winnipeg vaccine in monkeys at the U.S. Army Medical Research Institute of Infectious Diseases at Fort Detrick, Md.
"It's difficult to dissect out her response to the potential exposure with live wild-type Ebola virus versus the vaccine," says Geisbert, who is now associate director of the new National Emerging Infectious Diseases Laboratories Institute at Boston University.
"Not impossible, but more difficult. We've complicated it."
"But if it turns out that she really was exposed, if we find evidence of antibodies against ... an Ebola protein that we can absolutely say for certain she obviously saw (was exposed to) Ebola virus, then that clearly shows that the vaccine worked," he says.
http://www.thecanadianpress.com/eng...me=x040506A&newsitemid=346697028&languageid=1
© The Canadian Press , 2009