The overall effectiveness of last flu season's vaccine was only 29% because it didn't protect against a flu virus that appeared later in the season, according to the U.S. Centers for Disease Control and Prevention.
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It said the vaccine was 47% effective into February, but that dropped to just 9% after the late strain showed up, the Associated Press reported.
Flu vaccines are created each year to protect against flu strains predicted to be circulating in the upcoming season.
The effectiveness of last season's vaccine was the second lowest since 2011. The vaccine for the 2014-15 flu season was only 19% effective, the AP reported.
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