Advance shots protect those most exposed in possible pandemic, researchers suggest
WEDNESDAY, Oct. 8 (HealthDay News) -- People can be protected against a potential avian flu epidemic by getting advance shots of a vaccine that may or may not be effective against the strain causing the epidemic, British researchers suggest.
That apparently daffy strategy is scientifically sound, according to a letter in the Oct. 9 issue of the New England Journal of Medicine, because priming people with an old vaccine would make any new vaccine work faster and better.
A study of 24 people who got a now outdated avian flu vaccine seven years ago shows the strategy would work, said Dr. Iain Stephenson, a senior lecturer in infectious disease at the University of Leicester.
Those people quickly developed flu-fighting antibodies when challenged with the H5 avian flu strain that is regarded as the one most likely to spread from birds to humans and cause an epidemic, Stephenson said.
In June, U.S. researchers reported that they had developed a bird flu vaccine that appeared to be safe and more effective than the one currently approved for human use.
Three-quarters of volunteers produced antibodies against the virus after receiving a second dose of the vaccine, CELVAPAN, made by Baxter, compared with only 45 percent in the currently approved vaccine. Baxter conducted the study.
"If there were to be a pandemic of avian influenza, a vaccine would be the principal means of protecting the public," Stephenson said. "Because most people would be naive to the strain, it would very likely take two doses to produce an immune response. It is very challenging to give two doses."
And while governments have stockpiled vaccines against the H5 strain, "there are two problems," Stephenson said. "Is that vaccine a good match to the pandemic strain? H5 changes, and the emerging strain could be distant to the stockpiled vaccine.
"And considering the speed with which the pandemic might spread, even if you've got a stockpiled vaccine, it would be a challenge to use that vaccine in a two-dose strategy. But if you've got people who have been primed in advance, as we took people who were primed seven years ago, it's possible to give a single low-dose vaccine and show they get a rapid response that is reactive to all known strains."
"It's a very intriguing idea," said Ted Ross, an assistant professor of microbiology at the University of Pittsburgh Center for Vaccine Research.
Ross agreed that the current strategy of giving two flu vaccine shots two weeks apart might not meet the urgent needs of a pandemic. "I believe it is going to take too long in a bird flu pandemic," he said. "Priming the population might be protective against a wide variety of H5 viruses that we know have infected humans already. The broader the protection, the better."
However, there would be financial barriers to a program that would prime a large part of the population along the lines of the Stephenson proposal, Ross noted. "Even with the currently tested vaccine, there currently is no market for vaccinating people widely," he said.
Not everyone need be primed, Stephenson said. "You would be preparing for an event that might never happen, so safety considerations would be paramount," he said. "It is unlikely that the entire population would be covered. It might be proposed to take key personnel, first responders to a pandemic. That is a potential approach that should be considered."
Even then, a single study of 24 people is not enough to prompt such a program, Stephenson noted. "It is important that larger studies be done to confirm the finding," he said.
The status of avian flu vaccines is described by the Centers for Disease Control and Prevention.
SOURCES: Iain Stephenson, M.D., senior lecturer, infectious disease, University of Leicester, England; Ted Ross, Ph.D., assistant professor, microbiology, University of Pittsburgh Center for Vaccine Research; Oct. 9, 2008, New England Journal of Medicine
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