I have never had a flu shot.
There are 48 possible combinations of hemagglutinin (H1, H2, H3, H5, H6, H7, H9, H10) and neuraminidase (N1, N2, N6, N7, N8, N9) that have been detected in humans. H1N1, H2N2, and H3N2 are the most common that cause sustained infections, and these subtypes H5N1, H5N6, H7N2, H7N3, H7N7, H7N9, H9N2, H10N7, and H10N8 have been known to jump from animals to humans (Zoonotic Infections).
Every year, the vaccine makers select a H and N subtype to use in the vaccine. Efficacy depends on getting the right subtype combination for maximum effectiveness, and if they miss on what is going around, efficacy suffers.
So far, I just don't get the shots, and have only had the flu once or twice since they pulled the Swine Flu Vaccine under Gerald Ford's administration.