Last season's influenza vaccine was effective more than half the time, despite fears the shot was not an exact match for the flu strain that dominated the United States, the government said Thursday.
A study of more than 1,300 people in Colorado, including more than 300 who were lab-confirmed to have the flu, found that the vaccine worked about 52 percent of the time for healthy adults and 38 percent of the time for those with previous medical conditions, the Centers for Disease Control and Prevention reported.
The flu shot "still provided substantial health benefit," even though it's protection was much lower than the up to 90 percent protection that the vaccine affords when it's well-matched with the top strain circulating during a flu season.
The CDC said the effectiveness rate of the flu shot was similar to other years in which the vaccine's strains did not match what was circulating in public.
Health officials were concerned earlier last season about whether the flu shot would provide any protection against the type A-Fujian strain, which struck the country hard early last fall. That's because the closest strain in the vaccine's three-strain cocktail was the type A-Panama strain, a close cousin to the Fujian strain but not a perfect match.
The study also found that children who never before had a flu shot needed to be given two doses of the vaccine for protection against the virus. The CDC said those who only received one shot were no more protected than those who were not vaccinated.
The CDC interviewed 304 people in Colorado who were lab-confirmed for the flu and 1,055 other Colorado residents, checking to see whether the people had been vaccinated, had become ill or hospitalized. The agency calculated the vaccine's effectiveness by using the data to estimate the odds that the members of the study group had of becoming infected by the virus.
More than 150 children nationwide died during the flu season.
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On The Net:
CDC info: http://www.cdc.gov/mmwr
