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TUESDAY, Oct. 7, 2014 (HealthDay News) -- Two groups of researchers report they are refining the vaccine strategies that will be needed if the world ever has to face a "bird flu" pandemic.
Scientists suspect that avian influenza could change and easily spread to people with no immunity to it, potentially causing a global pandemic. By experimenting with ways to improve vaccines and boost the human immune response, these researchers hope to mute that threat.
In one study, researchers found that a vaccine for the H7N9 strain of avian flu worked much better when mixed with an adjuvant -- a substance that boosts the body's response to inoculation.
The other study reports that people vaccinated for an older strain of bird flu became "primed" for vaccines aimed at newer strains, with their immune systems displaying a heightened response to the new vaccine.
Both studies appear in the Oct. 8 issue of the Journal of the American Medical Association.
This sort of research helps lay the groundwork for the public health response required if a bird flu pandemic breaks out, said Dr. John Treanor, chief of infectious diseases at the University of Rochester Medical Center in New York, who wrote an editorial accompanying the research.
"It's useful to have all that information in hand, even though when the pandemic occurs you won't be able to mount an immediate vaccine response because you won't know which strain is involved," Treanor said. "You'd at least know what to use and how to make it, so you wouldn't be completely in the dark."
The first study studied the effectiveness of an experimental H7N9 vaccine made from an inactivated form of the virus grown in chicken eggs.
H7N9 bird flu has been on the public health radar since early 2013, when the first recognized cases involving that strain emerged in China.
The virus does not sicken birds, but causes illness in humans so severe that about two-thirds of reported cases require hospitalization, researchers said in background information. About 450 laboratory-confirmed cases, including 166 deaths, had been reported to the World Health Organization as of Sept. 4, 2014.
At this point, people mainly catch H7N9 through contact with poultry. "We have a great concern it could cause a very serious pandemic if it becomes efficient at moving from person to person," said study author Dr. Mark Mulligan, director of the clinical arm of the Emory Vaccine Center at Emory University School of Medicine in Atlanta.
Researchers tested the experimental H7N9 vaccine in 700 adults aged 19 to 64, randomly administering either the vaccine alone or the vaccine mixed with an adjuvant called MF59.
MF59 "enhances the ability of the vaccine to trigger a stronger immune response" by drawing the attention of the immune system to the virus cells in the vaccine, Mulligan said.
The experimental vaccine on its own produced a minimal immune response against H7N9, researchers found.
But when mixed with MF59, the vaccine created a significant immune response in 59 percent of participants.
Younger people responded even better. About 80 percent of the younger third of the subjects, aged 19 to 34, mounted an effective immune response, Mulligan said.
"It gives us an indication that we can produce an immune response in most people that will be protective," Mulligan said. "If the virus does change and become efficient, and we do see the pandemic threat become actualized, it's very nice to know we have this vaccine available."
The other study involves an existing vaccine that targets an older strain of bird flu known as the "Vietnam" strain.
Researchers wanted to find out if, by using the older vaccine, they could prime the immune system's memory and improve its response to newer bird flu vaccines, explained study author Dr. Robert Belshe, a professor of infectious diseases at Saint Louis University School of Medicine.
A year after 72 participants had been inoculated against the Vietnam strain, researchers gave them a vaccine aimed at preventing a newer bird flu strain known as "Anhui."
These participants displayed a boosted immune response when compared to 565 people who only received the Anhui vaccine, researchers found.
"Our immune system remembers it has been infected with a similar virus in the past. If we get exposed again, that immunologic memory kicks in very quickly and creates antibodies that kill the new virus much quicker," Belshe said.
This strategy could be used to help protect lab workers doing research on bird flu or field workers who are investigating outbreaks, he said.
"The priming itself might benefit them, or it would make their response stronger," Belshe said.
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SOURCES: John Treanor, M.D., chief, infectious diseases, University of Rochester Medical Center, Rochester, N.Y.; Mark Mulligan, M.D., director, clinical arm, Emory Vaccine Center, Emory University School of Medicine, Atlanta; Robert Belshe, M.D., professor, infectious diseases, Saint Louis University School of Medicine, Saint Louis, Mo.; Oct. 8, 2014, Journal of the American Medical Association