CDC: Flu vaccine reduces risk by 23 percent

This year's flu vaccine reduced a person's risk of going to the doctor because of the flu by 23 percent across all age groups, according to data out this week from the Centers for Disease Control and Prevention.

Since the CDC began conducting annual flu vaccine effectiveness studies in 2004-2005, overall estimates for each season have ranged from 10 percent to 60 percent effectiveness in preventing medical visits associated with the flu.

This season's vaccine offers reduced protection because about 70 percent of flu cases appear to be a drifted influenza A (H3N2), strain, which means the virus circulating is different from the flu viruses used in the vaccine.

During seasons when vaccine viruses and circulating influenza viruses are well matched, vaccine effectiveness can be between 50 and 60 percent, according to CDC.

Other factors influencing how well the flu vaccine works is the age and health of the person being vaccinated. In general, the flu vaccine works best in young, healthy people and is less effective in people 65 and older.

This pattern is reflected in the this season's early estimates for vaccine effectiveness against the H3N2 viruses - vaccine effectiveness was 26 percent for children aged 6 months through 17 years, 12 percent for those aged 18 to 49 years and 14 percent for people aged 50 years and older.

Even still, the CDC recommends flu shots for everyone 6 months of age and older. It is especially important for young children, people 65 and older and pregnant women. Manufacturers have made and distributed about 145 million doses, which the CDC said is a sufficient supply.

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