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Panel: Overhaul Next Year's Flu Vaccine

Experts Recommend Replacement of Virus Strains in Vaccine
By
WebMD Health News
Reviewed by Louise Chang, MD

Feb. 22, 2008 -- A government scientific advisory board recommended for the first time this week a complete overhaul of the makeup of the flu vaccine for next year.

The move would replace all three flu virus strains in this year's vaccine with three new strains for next year. The shift could complicate manufacturers' efforts to grow and produce new vaccine in time for next year's flu season, officials say.

"It's a little unpredictable" whether the overhaul will cause delays as vaccine makers grow the new strains and produce new flu shots, says Nancy Cox, PhD, head of the CDC's influenza division.

Predicting Flu Virus Strains

Experts meet under the auspices of the FDA each year to try to predict which flu virus strains are most likely to spread across the U.S. in next yearly flu season. They use samples from the Far East, where yearly flu strains typically start, but the prediction is part science and part guessing game.

The flu vaccine is called a "trivalent" vaccine because it contains three separate flu strains. Most years experts manage to match their vaccine design in the spring to the strains that actually circulate throughout the country later in the year.

But not this year. In the winter of 2007, experts considered including a particular H3N2 strain of influenza A, but dropped the plan when they couldn't find samples that would grow properly in the manufacturing process.

Influenza A typically makes up about 85% of all flu cases. And this year, the particular H3N2 strain that was left out of the vaccine wound up being the dominant influenza A virus; it accounts for more than 60% of flu cases.

"We simply came up empty-handed," Cox tells WebMD.

Possible Complications for Vaccine Makers

At its annual February meeting Thursday, experts for the first time recommended replacing all three strains in this year's vaccine with three new ones for next year. That could cause complications as manufacturers try to grow and mass-produce vaccine from the new strains.

Cox says manufacturers will "have a jump on the situation" because two of the strains were also recommended in September 2007 for vaccine makers in the Southern Hemisphere. Experts hope that will make production simpler in the Northern Hemisphere. 

This year's vaccine mismatch has caused worries that the flu vaccine is ineffective. Officials say they don't have any evidence that extra flu cases are occurring because the particular strain of H3N2 is not included in the vaccine.

"We still recommend that individuals take the vaccine even though the strain is off," said Norman Baylor, PhD, head of the office of vaccines research and review at the FDA.

Department of Defense scientists said Thursday that this year's flu vaccine is about 85% effective at preventing illness in young, healthy military personnel. Baylor said that's about the effectiveness that researchers expect. But young, healthy military recruits are also much more likely to respond to the vaccine than infants, the elderly, or chronically ill people who are urged to get the vaccine.

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