Just going by people I know, the ones getting "flu shot" every year are always sick from one thing or another. Won't eat stuff that will actually combat the symptoms. Don't get it that building up immune system is the main thing. Too convenient to keep grabbing shit off shelves /calling "the doctor" for quick fixes.
Don't help that everyone is constantly reminding the sheep to get the damn things. Unfortunately, they watch tv. Also, try walking into a store for anything without getting literally harassed every single time about "have you gotten your FS yet"? Even Libraries have had signs up for the shit. Last time I had it was 14 years ago because workplace had us get them. Never again.