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French Bird Flu Vaccine No Panacea

Immune Boost Lowers Vaccine Dose, but Much More Work Ahead
By
WebMD Health News

May 10, 2006 -- An immune-boosting substance makes an experimental bird flu vaccine work better -- but probably not well enough to stop a flu pandemic.

The finding comes from a human safety study of Sanofi Pasteur's experimental bird flu vaccine. The study explored whether an immune-boosting substance known as an adjuvant -- alum, the only adjuvant currently approved for human use -- might make a bird flu vaccine work better.

That would be a very good thing. Vaccines based on bird flu proteins seem to work only in higher-than-expected doses. Current technology produces these proteins in hens' eggs -- a process that takes a lot of time and effort. Adjuvants are a "dose-sparing" technology that might increase the number of vaccine doses available in an emergency.

"We have tested this vaccine in 300 volunteers," says Melanie Saville, MD, a researcher for the France-based pharmaceutical company Sanofi Pasteur. "The vaccine in different doses and with adjuvant is safe and well tolerated, and we demonstrate an immune response in many individuals. These are encouraging results, but clearly we need more work."

The findings appear in the May 11 early online edition of The Lancet.

The Good/Bad News

Whether the French report is encouraging depends on how you look at it, says Richard Compans, PhD, head of microbiology and immunology at Atlanta's Emory University School of Medicine.

"On the positive side, it has been possible to generate some experimental vaccines that show an effect that may be protective in at least some proportion of recipients," Compans tells WebMD. "On the negative side, the response isn't as strong as one would expect from the current seasonal flu vaccine. There is something special about this [bird flu] protein that makes it less effective as a vaccine component. We don't know what that is. But it doesn't mean it can't be overcome by other approaches."

Saville and colleagues used alum to boost immune responses to a bird flu version of Vaxigrip, a seasonal flu vaccine used in Europe. Two doses of the experimental bird-flu vaccine were given three weeks apart to healthy adult volunteers.

At the highest dose tested, the plain-vanilla version of the vaccine elicited levels of anti-bird-flu antibodies expected to be effective in 52% of volunteers. When given with alum, the high-dose vaccine was 67% effective.

Unexpectedly -- and disappointingly -- the alum adjuvant did not boost immune responses to lower doses of the vaccine. That may be because alum is simply not a very good adjuvant, suggests immunologist David Topham, PhD, of the University of Rochester, N.Y.

"Anything approved for human use is judged on side effects and reactions," Topham tells WebMD. "If it is benign in not causing a lot of negative reactions, it gets approved. Alum is good in that regard. But as an adjuvant, it is not very good at all. It is arguable whether it is better than not using an adjuvant at all, judging from this data. And it didn't work at all at the lower doses."

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