There are a handful of factors, I'll approach this as if you're acting in good faith. 1) Most people who claim to have "the flu" don't actually have influenza.

There are a handful of factors, I'll approach this as if you're acting in good faith. 1) Most people who claim to have "the flu" don't actually have influenza. Thus, if they take a flu vaccine, and get "the flu", they blame the flu 2) The vaccine does not create a perfect boundary. It's a population scale benefit. It makes it less likely one gets infected, it makes it less likely that someone who gets infected has serious disease, and it makes it less likely that someone infected passes it along 3) The "flu vaccine" is a prediction, trying to guess the strains that will be prevalent in the upcoming season Sometimes they guess wrong, and it's less effective. If we supported mRNA technology this could be improved.