Ebola lab accident could reveal information about experimental vaccine
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.
'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.' — Dr. Heinz Feldmann
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," said 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 that 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.
Safety test
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.
Cost remains an obstacle to testing experimental vaccines for Ebola and similarly deadly viruses, scientists say.
An Ebola vaccine made at the National Microbiology Laboratory in Winnipeg was given to an unnamed German scientist who accidentally pricked herself with a syringe containing Ebola.
Researchers hope that her blood will reveal if the vaccine helped save her life.
"There is a lot of interest at the moment and some people find it positive that ... the vaccine was offered and actually given to her," said Dr. Heinz Feldmann, who led the team that designed the Ebola vaccine as well as one for a cousin virus, Marburg.
"The question remains the money."
Ebola and Marburg viruses trigger ghastly viral hemorrhagic fevers that kill between 50 and 90 per cent of those who become infected.
Despite promising results in animal trials, financial, logistical and regulatory hurdles block the development of emergency stocks of test lots for the vaccines.
Source: Canadian Press
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.
Unanswered questions
Feldmann believes, given the woman's lack of symptoms, that this may be the most likely scenario.
"That is my worry," he said. "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 said.
"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 ones that respond to the non-Ebola proteins in the vaccine and for ones generated by the virus itself.
Antibody search
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," said 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 said.