New Bird Flu Vaccine Shows Promise

WEDNESDAY June 11, 2008 -- Scientists have succeeded in developing a whole-virus bird flu vaccine that appears to be safe, more effective than the one currently approved for human use and also able to be manufactured much more quickly than conventional vaccines.

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.

Importantly, the study confirms the feasibility of using new, cell culture-derived vaccine.

"The fact that they were able to do this, and very efficiently, and get such good antibody response reinforces and reconfirms that, even for the annual flu virus, we need to move away from embryonated hens' eggs [the current method for producing vaccines] and move to cell cultures," said Dr. Pascal James Imperato, dean of the graduate program in public health at the State University of New York (SUNY) Downstate Medical Center in New York City and a former New York city health commissioner.

"We don't know if [the bird flu] ever really did become a pandemic [what protection this would afford]," Imperato added. "But this gives us some reassurance that there would at least be a mechanism to rapidly produce this vaccine."

"CELVAPAN is unique in that it provides protection among several bird flu virus strains, can be produced in about less than half the time of traditional methods and does not require an additive to boost an immune response," said study author Dr. Hartmut J. Ehrlich, vice president of Baxter Global Research & Development, in Vienna.

"Baxter has submitted for licensure with the EMEA [European Medicines Agency] and has two programs with the U.S. government for flu vaccine development for the U.S. market," Ehrlich said. "Additionally, Baxter is working with health authorities around the world to help them prepare for a pandemic. Baxter partners with governments on research and development, offers a vaccine stockpile and capacity planning to be used in the event a pandemic is declared. Several governments have already received stockpiles and have made advance purchases of capacity."

The hunt for a good bird flu vaccine to be used in humans has gone on for some 10 years, since the H5N1 family of avian flu first emerged in Hong Kong, said the author of a perspective accompanying this latest study, both published in the June 12 issue of the New England Journal of Medicine.

In the past two years, the H5N1 strain of avian flu has infected poultry throughout Southeast Asia, Central Asia, Africa and Europe, prompting the destruction of millions of birds. So far, more than 100 people have died worldwide from H5N1 infection, which has been spread through close contact with birds.

Experts fear that the virus will acquire the ability to jump easily between humans, leading to a pandemic and millions of deaths. Unlike the seasonal flu, humans have no immunity to bird flu.

Last year, the U.S. Food and Drug Administration approved an admittedly less-than-perfect vaccine against bird flu, the first such vaccine to be approved for humans. At the time, the vaccine was described as an "interim measure."

Producing and distributing enough vaccine to protect large populations is a key problem.

For the past 50 years, vaccines have been made using a cumbersome egg-based technology, which requires weakened virus injected into hundreds of millions of fertilized hens' eggs each year. The process takes about six months to be completed and has to be repeated as virus strains change.

The Vero cell technology used here uses "wild type" virus (the strains existing in nature) grown directly in cell culture, allowing more of the vaccine to be produced in a shorter amount of time (about 12 weeks).

The vaccine also didn't need an adjuvant, a substance added to a vaccine to make it stronger. There have been safety concerns about adjuvants.

Researchers were also able to use a whole virus, thought to produce better immunity responses, without any major side effects.

"We had been concerned with the idea that whole viruses have more side effects, but this doesn't show that," said Dr. Marc Siegel, an associate professor of medicine at New York University School of Medicine, and author of Bird Flu: Everything You Need to Know About the Next Pandemic.

CELVAPAN was tested on 275 adults aged 18 to 45, all of whom received two doses 21 days apart. Not only did the vaccine produce an immune response against the A/Vietnam/1203/2004 virus strain, but also against two related strains.

With all the successes demonstrated here, experts still point to some caveats. One is that the vaccine was only tested in younger adults (up to 45 years of age), not older adults where it would be most needed.

"We don't know how older adults would respond in terms of antibody levels," Imperato said. "We know that younger adults tend to form antibodies to influenza vaccines much better than older adults."

Having to give two doses is also a drawback. "As soon as you have to give two doses of a vaccine, even if it's not at a very long interval, it presents a problem with public compliance," Imperato said.

And there are many who believe bird flu will not result in a major threat to humans. "I still think there's no reason to believe that a virus that's so pathogenic to birds is automatically going to become pathogenic to humans," Siegel said. "In fact, most pandemics come from low-pathogenic viruses. We've got to watch this carefully, because it's such a killer [mortality rate is upwards of 60 percent in humans], but that doesn't mean by any stretch of imagination that it's going to become a human virus."

More information

The U.S. Centers for Disease Control and Prevention has more on bird flu.

Posted: June 2008


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