In addition, while this year's vaccine was considered a good match for the most common circulating flu viruses, it only provided 47% protection against H3N2, the main virus.

CNN: Flu vaccine less effective, especially among elderly

This year's vaccine is well matched to the circulating viruses and, while not perfect, provides good protection.

CNN: In the future, get vaccinated earlier

The match for influenza B viruses, the second-most common this season, wasn't as good.

CNN: Had a flu shot? You'll be OK -- maybe