By Rob Stein, NPR
As expected, this year's flu vaccine looks like it's pretty much of a dud.
The vaccine only appears to cut the chances that someone will end up sick with the flu by 23 percent, according to the first estimate of the vaccine's effectiveness by the federal Centers for Disease Control and Prevention.
The CDC had predicted this year's vaccine wouldn't work very well because the main strain of the flu virus that's circulating this year, known as an H3N2 virus, mutated slightly after the vaccine was created. That enables the virus to evade the immune system response created by getting vaccinated.
The effectiveness of the flu vaccine varies dramatically from year to year, but can be as high as 50 percent to 60 percent, the CDC says. So if the early estimate of this year's vaccine's effectiveness, reported in this week's Morbidity and Mortality Weekly Report, holds up, it would put the protection at the low end.