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Bird Flu Vaccine: 'A Long Way to Go'

In Race to Make Bird Flu Vaccine, Finish Line Still Out of Sight
WebMD Health News
Reviewed by Louise Chang, MD

March 29, 2006 - An experimental bird flu vaccine seems to work. But it's nowhere near ready for prime time.

That's the word from U.S.-sponsored clinical trials of an H5N1 bird flu vaccine made by Sanofi Pasteur. The study shows that two shots of the vaccine given four weeks apart -- at the highest dose tested -- give what should be protective immunity to 50% of healthy adults.

High doses. Limited effectiveness. This means the current vaccine isn't likely to stem a deadly pandemic if the bird flu starts spreading among people.

"We have a long way to go," Anthony S. Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, said at a news conference. "It is a step in the right direction. It is paving the way for when we have a product that is much more robust."

The need for high doses means the current U.S. stockpile of the vaccine will cover only 4 million people.

"We are certainly not where we want to be on stockpiling a vaccine that is fully effective," Fauci said. "If we had a bird flu pandemic now, we would have to rely much more on public health measures than on vaccine."

Stretching the Bird Flu Vaccine Stockpile

Practical use of the current bird flu vaccine will almost certainly mean giving the vaccine along with an immunity-boosting substance called an adjuvant. This would greatly reduce the amount of vaccine needed for immunity, stretching vaccine stores while at the same time improving the vaccine.

Clinical trials of bird flu vaccines with adjuvants have only just begun, notes study leader John J. Treanor, MD, director of the vaccine and treatment evaluation unit at the University of Rochester in New York.

"Every journey starts with the first step," Treanor said at the news conference. "We are starting to iron out the regulatory and manufacturing issues. We have a product and we are testing it. We have a really good idea of what the immune response to the vaccine is. We are not there yet, but we are making progress."

Treanor announced preliminary resultspreliminary results from the bird flu vaccine study last August, so the current report -- in the March 30 issue of The New England Journal of Medicine -- comes as no surprise.

"Earlier studies suggested immunity would take a larger dose of H5N1 vaccine than regular flu shots," Treanor said. "So I don't think anyone was shocked. ... We certainly had hoped it would be better but we are not surprised."

In fact, the vaccine may very well work better than it appears. Treanor and colleagues were looking for antibody levels that seemed to protect people during a 1997 outbreak of H5N1 bird flu virus in Hong Kong. While high-dose bird flu vaccine stimulated this kind of antibody response in only half of study recipients, Treanor says lower antibody levels may very well be protective.

If that's the case, the vaccine may actually be better than it now looks. But there's no way to tell. Bird flu is not spreading among humans. And researchers, of course, aren't exposing any study volunteers to potentially lethal bird flu virus.

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