Scientists have figured out why last year's flu shot was so ineffective.
They say the H3N2 strain of the virus mutated while it was being grown in chicken eggs.
Long story short, the mutation made it harder for the human body to recognize the virus.
The CDC estimates the 2016 flu shot was only 42 percent effective against H3N2.
Researchers are recommending the medical industry find a different way to grow the vaccine.