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MELISSA BLOCK, host:

Now, to news about health and disease.

In a few minutes we'll hear surprising news about middle-aged women and the risk of stroke.

First, a report about next year's flu vaccine.

ROBERT SIEGEL, host:

A group of experts told the Food and Drug Administration today which flu viruses should go into next year's flu shots. It's only an educated guess but the advisers to the FDA hope that they'll do better than this year. Two of the three strains in the current vaccine turned out not to be good matches for the viruses that are actually making people sick.

NPR's Richard Knox has that story.

RICHARD KNOX: In any given year, there's not just one flu virus getting passed around, there are usually three. So a flu vaccine is really three vaccines in one shot. And for next year, the experts are recommending that all three of the viral strains in the vaccine be replaced.

Dr. Norman Baylor of the FDA says that may be unprecedented.

Dr. NORMAN BAYLOR (Food and Drugs Administration): It's very rare for us to have to change all three strains. I can't remember this happening since I've been here.

KNOX: Usually, one or two of the vaccine's strains is a holdover, but all three of this year's flu viruses have changed genetically from ones prevalent a year ago.

Dr. Nancy Cox of the Centers for Disease Control and Prevention says next year's vaccine is an attempt to catch up to what the flu is doing today.

Dr. NANCY COX (Influenza Division Director, Centers for Disease Control and Prevention): The strains that have been recommended as the northern hemisphere vaccine strains for next season are well matched to the strains that are circulating in the United States and globally at the moment.

KNOX: But that's not to say those will be the ones causing illness a year from now. In fact, two of the three strains in this year's vaccine are not a good match for the viruses circulating now. They emerged after last February's vaccine decision. That means this year's vaccine is only about 50 percent effective in preventing someone from getting the flu although it probably will reduce the severity of illness.

Cox says these mismatches are almost inevitable.

Dr. COX: The problem is that the vaccine strain recommendations have to be made almost a year in advance of the peak of the influenza season, so what we're trying to do is to keep up with the viruses that are circulating in many, many countries around the world.

KNOX: The reason flu vaccine decisions have to be made so far in advance is that it's not easy to make a flu vaccine. Once officials make their best guess about which viruses to put in the vaccine, those viruses have to be modified to grow in specially produced chicken eggs. Some don't grow very well, so it takes longer to get enough to make the 130 million doses the government asks manufacturers to crank out.

Officials place great hope in a new flu vaccine technology that will get rid of eggs. Flu viruses will be grown in big vats of animal cells. But Dr. Michael Osterholm of the University of Minnesota says this so-called cell culture technology will only reduce vaccine lead time by a little.

Dr. MICHAEL OSTERHOLM (University of Minnesota): The system is just not going to work. By moving the cell culture, all we're doing is taking an old, bad vaccine system and putting new tires on it - that's all we're doing.

KNOX: Rather than tinker with the old machinery, Osterholm says the nation should launch a push to revolutionize flu vaccines.

Dr. OSTERHOLM: The bottom line is that somebody needs to take a step back and say this current system isn't working. We really need a universal vaccine.

KNOX: That is, a vaccine made up of the unchanging parts common to all strains of flu viruses. That's the approach used with other vaccines such as hepatitis B, but with highly changeable flu viruses, they would be a huge challenge. There's some reason to think it's possible but not any time soon.

Richard Knox, NPR News.

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