I had a mild flu last year. I think it was because my defences were down following my broken arm incident.
Clive has the jab for free because he has Type 1 Diabetes. He’s never had flu. Nor any side effects that I can attribute to it.
One time years ago I went to my GP about something and he said, While you’re here shall I give you a flu jab? So I figured why not? Like all previous years and every year since (until last year - which was extraordinary circumstances) I didn’t get flu. But that particular year I didn’t get a cold either. Which is highly unusual.