I haven't had my flu shot for over three years. My immune system is amazing. I literally never get sick. Probably because it built up so well when I got sick a lot as a child. My parents were not super protective over me playing in dirt or other things. I haven't had the flu, a cold, or anything else in years. A few years ago when I DID get my flu shot, I got sick for like two weeks immediately afterwards. Puking, fever, everything.