CMAJ : Canadian Medical Association journal = journal de l'Association medicale canadienne
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Multicenter Study
Repeated influenza vaccination for preventing severe and fatal influenza infection in older adults: a multicentre case-control study.
The effectiveness of repeated vaccination for influenza to prevent severe cases remains unclear. We evaluated the effectiveness of influenza vaccination on preventing admissions to hospital for influenza and reducing disease severity. ⋯ Among older adults, repeated vaccination for influenza was twice as effective in preventing severe influenza compared with nonsevere influenza in patients who were admitted to hospital, which is attributable to the combination of the number of admissions to hospital for influenza that were prevented and reduced disease severity. These results reinforce recommendations for annual vaccination for influenza in older adults.