Seniors were one of the main groups urged to get a flu shot this season.
But for many of them the vaccine didn't work.
The CDC says the vaccine has helped just 9% of people of those who are 65 and older.
For those under 65, the vaccine is about 56% effective.
Researchers say they're not sure why this vaccine isn't as good this year.
But, even with the disappointing numbers, the CDC says it's still worth it to get a flu shot.