Bird Flu Vaccine: Long Way To Go

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 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.

New Vaccine Techniques

Regardless of how well this vaccine works, all kinds of new bird flu vaccines are in the works. In one major step forward, the U.S. government is helping vaccine manufacturers move from the tried-and-true method of growing vaccine virus in chicken eggs to much faster cell-culture techniques.

Speed may in fact be the name of the game. That's why this study is so important. Bird flu vaccines now under development will pave the way for rapid licensing of newer vaccines. And new vaccines will be needed, fast if the bird flu virus mutates to a form that causes a human pandemic.

"This virus, if it evolves to the point of being able to spread from human to human, would be different than the Vietnam 2004 strain tested and reported here," Fauci said.

"But we hope that simultaneously with testing these vaccines, and getting good feel for the scope and tolerability of this vaccine, we would do two things. We will stockpile a modest amount, so even if there is not a perfect match, there would be some benefit. At the same time, we would isolate the putative virus that would go from person to person and develop a vaccine for that."

Sources: Treanor, J.J. The New England Journal of Medicine, March 30, 2006; vol 354: pp 1343-1351. Poland, G.A. The New England Journal of Medicine, March 30, 2006; vol 354: pp 1411-1413. Katz, J.M. Journal of Infectious Diseases, December 1999; vol 180: pp 1763-1770. News conference with Anthony S. Fauci, MD, director, National Institute of Allergy and Infectious Diseases, Bethesda, Md., and John J. Treanor, MD, professor of medicine and director, vaccine and treatment evaluation unit, University of Rochester, N.Y.
By Daniel J. DeNoon
Reviewed by Louise Chang, M.D.
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