The flu vaccine for 2014-2015 is not the worst ever -- the past decade has ranged from 10 per cent to 60 per cent effective -- but its record is worrying enough that the Centers for Disease Control and Prevention have urged doctors to ramp up the use of antiviral medications in people who fall ill with influenza.
Its lack of punch is being blamed on multiple strains of the H3N2 virus that are circulating and making people sick, but that were not included in this season's vaccine.
The flu vaccine is generally most effective in young, healthy people under 65.
This season, vaccine effectiveness has been highest -- 26 per cent -- in those aged six months through 17 years.
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Vaccine effectiveness was just 12 per cent for ages 18 to 49 years and 14 per cent for people age 50 years and older, the CDC said.
The CDC is still recommending that people get a flu shot because it may help prevent severe infections and complications that lead to hospitalization or even death.