French Bird Flu Vaccine No Panacea
Immune Boost Lowers Vaccine Dose, but Much More Work Ahead
May 10, 2006 -- An immune-boosting substance makes an experimental bird flu
vaccine work better -- but probably not well enough to stop a flu
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
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
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."