U.S. flu vaccine effectiveness lower than usual: health official

Based on findings from a community in central Wisconsin that served as a test case, people who were vaccinated were 44 percent less likely to get influenza than unvaccinated people, the U.S. Centers for Disease Control and Prevention said. That compares to typical vaccine effectiveness of around 70 percent or higher, CDC officials said.

The CDC and the World Health Organization have recommended a complete reformulation of next year’s flu vaccine because of the poor match during the 2007-2008 flu season, which officials have described as moderately severe.

This year’s study confirmed suspicions that two of the three strains of flu most likely to cause disease had “drifted,” or evolved, away from the cocktail used in the vaccine.

Flu infects from 5 percent to 20 percent of the U.S. population each year and kills an estimated 36,000 Americans in an average year, most of them elderly. It also can kill young children. This season, the CDC counted 66 child deaths from flu.

The vaccine is designed to protect against three influenza strains — two from Type A, an H1N1 and an H3N2 version, and one for Type B. “This season, we had a less-than-optimal match in two of the three vaccine components,” Dr. Dan Jernigan of the CDC’s Influenza Division told reporters.

It is tricky to compare vaccine effectiveness year to year because the CDC has used various tools and different populations to track it but it appears this year’s vaccine effectiveness may be the lowest since the 1997-1998 flu season. The vaccine must be reformulated every year because the viruses mutate so much.

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