This year's flu shot was only 44% effective, a new study suggests -- the least effective flu vaccine in a decadeز

The findings come from a study of 616 Wisconsin residents who came down with flu-like illnesses during the peak of the flu season. Study findings appear in today's issue of the CDC's Morbidity and Mortality Weekly Report.

In good years, flu vaccines are 70% to 90% effective in preventing confirmed cases of flu bad enough to cause a person to seek medical attention. This year's vaccine appears to be the least effective since the 1997-1998 flu season, when the vaccine was about 50% effective.

Two of the 2007-2008 flu vaccine's three components didn't match most of the flu viruses circulating this flu season. This season's predominant flu bugs have been the mismatched type A H3N2 and type B strains.

The H3N2 component was only a partial mismatch, cutting the vaccine's effectiveness against type A flu to 58%. The type B flu component did not match at all -- and the vaccine seems to have had no effect against this bug.

Dan Jernigan, MD, MPH, deputy director of the CDC's influenza division, takes an optimistic, glass-half-full view of the study findings.

"While the vaccine's effectiveness against H3N2 is less than might be expected ... the evidence suggested that the vaccine provided substantial protection," Jernigan said at a CDC news conference. "The measurable effectiveness of the vaccine in this study suggests we continue to recommend vaccination even in years of mismatch."

That's true: The vaccine's 44% effectiveness is a lot better than the 0% effectiveness of no vaccination at all.

And that's good news for the record number of Americans who got their flu shots this year. Vaccine companies delivered 113 million doses of flu vaccine.

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