All three flu viruses in this year's vaccine should be swapped for others next year because of a dramatic change in the mix of circulating flu bugs, a U.S. government advisory panel is expected to recommend today.
The change, first proposed last week by the World Health Organization (WHO), marks the first time in years that health experts advocate a complete vaccine overhaul. A Food and Drug Administration advisory panel will vote on the recommendation today. "I can't remember when we've changed all three," says Norman Baylor, director of the FDA's Office of Vaccine Research and Review.
Typically, public health officials recommend replacing one or two of the three viruses in the vaccine, because dominant flu viruses tend to circulate for a year or two before giving way to a new strain.
Deciding which viruses to include in each year's vaccine is a complicated task, Baylor says. It involves crunching information from 80 WHO collaborating labs worldwide to predict which of the viruses circulating during the winter in Asia and the Southern Hemisphere are likely to cause serious illness in the Northern Hemisphere.
The decision launches a "time-critical, highly orchestrated" effort by public health agencies and vaccine makers to produce roughly 100 million doses of vaccine in six to eight months -- a dated process that involves growing the virus in eggs, he says.
This year's vaccine protects against just one of three viruses that are dominating this year's flu season, which is now reaching its peak. The Centers for Disease Control and Prevention said last Friday that 44 states were reporting widespread flu activity, and cases were mounting in five others.
"We thought we were going to have a pretty mild season until two weeks ago," says Nancy Cox, director of the CDC's flu division and the WHO center that oversees flu-fighting efforts worldwide.
This year's vaccine contains two influenza "A" viruses, from the Solomon Islands and Wisconsin, and a "B" virus from Malaysia. "A" viruses are the most dangerous, says flu expert William Schaffner of Vanderbilt University, while "B" viruses cause smaller outbreaks.
The viruses that are in the vaccine now have been around the USA for some time, so the population has built up immunity through infection and vaccination, Schaffner says. But influenza has the capacity to change, and as soon as it changes, people become more vulnerable. "Why suddenly there were changes in all three major strains is inexplicable," he says.
Only the Solomon Islands virus in the vaccine matched up with a virus now causing illness in the USA. Another "A" virus, from Brisbane, which was overlooked in the process of formulating this year's vaccine, turned out to be the culprit causing most of this year's disease.
Next year's recommendation calls for two very different viruses that were both isolated in Brisbane: A/Brisbane/59/2007 and A/Brisbane/10/ 2007, which is the version now widely circulating in the USA. The third component is B/Florida/4/2006.
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