Totally anecdotal - but I got a flu vaccine once in my life and it was way before vaccines were even on my radar. I just don't like needles so never got one, but 1 year got talked into it. approximately 1 week later I came down with the most God Awful "flu like illness" I've ever had in my life. I missed 10 days of work and wished for death....ugh it really was awful. I haven't had the flu vax since. I think I got the flu (or FLI) once more about 9 years ago, but it wasn't as bad. Since I started paying very close attention to my vitamin d levels and keeping them nice and high - have not had the flu since.
Also anecdotal but this flu season I knew 8 people who came down with the flu - or flu like illness since I don't think any of them had lab confirmation. 6 of the 8 were vaccinated. The ones who were unvaccinated recovered more quickly too