02 May 2006
U.S. Medical Agency Funds Successful Bird Flu Vaccine Test
New vaccine protected mice, ferrets against lethal H5N1 virus
Washington – A commercially developed vaccine funded by the U.S. National Institutes of Health has protected mice and ferrets against a highly lethal avian influenza virus.
California company Vical Inc., developed the vaccine, and an investigator at St. Jude Children's Research Hospital in Tennessee led the study, according to a May 2 St. Jude press release.
The finding, coupled with results of previous studies that showed protection against multiple human influenza strains, suggests that such a vaccine would protect humans against multiple variants of the bird and human influenza viruses, said Richard Webby of St. Jude.
Such a vaccine could protect people against an H5N1 bird flu virus that mutates to adapt to humans, not just birds, and easily can spread from person to person, Webby said.
Flu experts and public health officials fear that such a variant of H5N1 would trigger a human pandemic.
The studies included 16 mice or six ferrets in each vaccine or control group, and the investigators used two versions of Vical's DNA-based vaccine in the studies.
One vaccine was directed against three viral proteins – NP, M2 and H5.
NP and M2 usually do not mutate quickly (they are “conserved”) and are slow to avoid immune responses that a vaccine triggers.
H5 is a mutating (“variable”) protein on the surface of the bird and human flu viruses that is critical to the viruses’ ability to infect cells. The H5 protein easily mutates, so it can avoid immune responses triggered naturally or by a vaccine.
The other vaccine used in the study contained only the two conserved viral proteins, NP and M2.
All test DNA vaccines were formulated with the company's VaxfectinTM adjuvant. An adjuvant is an additive administered with a vaccine that has little effect by itself, but improves the response of the immune system to the vaccine.
In the St. Jude study, the three-component vaccine (H5, NP, M2) protected the mice completely against potentially lethal challenges with a highly virulent H5N1 avian influenza virus.
Other studies showed that a version of the vaccine containing only the NP and M2 components provided significant protection against several strains of human influenza virus and the H5N1 bird flu strain.
"By stimulating immune responses against targets not likely to mutate,” he added, “the vaccine could trigger an immune defense against a broad range of variants of the virus.”
Even if the bird flu virus mutates to adapt to humans, Webby said, cross protection would let the immune system track and attack such an emerging new variant “without missing a beat.
“We wouldn't have to wait to start developing a vaccine against it until after the original virus mutated,” he added, which would have to be done now if bird flu adapted to become transmissible between humans, the mutation that could lead to a human pandemic of disease.
Webby's team showed that all mice and ferrets that received the DNA vaccine survived the challenge with the virulent H5N1 strain; those that received a "blank" (placebo) vaccine did not survive.
The vaccine also prevented weight loss in all animals challenged with the virulent virus, suggesting that the vaccine might also protect humans against serious flu-related sickness. The DNA vaccines targeted NP and M2 – with and without the H5 avian influenza virus surface protein.
The St. Jude Hospital press release is available on its Web site.
For additional information on efforts to combat avian influenza, see Bird Flu.
(Distributed by the Bureau of International Information Programs, U.S. Department of State. Web site: http://usinfo.state.gov)
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