New Bird Flu Vaccine Shows Promise

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 ofBird 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.

SOURCES: Hartmut J. Ehrlich, M.D., vice president, Baxter Global Research & Development, Vienna; Pascal James Imperato, M.D., dean, graduate program in public health, State University of New York, Downstate Medical Center, New York City; Marc Siegel, M.D., associate professor, medicine, New York University School of Medicine, New York City, and author,Bird Flu: Everything You Need to Know About the Next Pandemic; June 12, 2008,New England Journal of Medicine