The flu vaccine doesn't help you build up an immunity to influenza, just like the COVID vaccine doesn't give you immunity to COVID. If anything, the flu vaccine hampers a person's natural immunity. I've had one flu shot in my entire life, and very seldom ever catch the flu, or even a cold. When I do catch the flu, it's very mild and goes away in a couple days, just like COVID did when I caught in back in 2020. It was like a three-day mild flu and I just slept it off. Haven't had a resurgence of it since then, even though I never wear masks and go a lot of places where there are crowds of people.