I had a sudden attack of 'flu in March 1988 and again exactly 12 months later. Vaccines weren't offered then. Until Covid when vaccinations was encouraged, I hadn't bothered with getting a jab, however due to not being in the age group of the Covid Vac this year, I opted for the 'flu one instead.
Any1 who 'walks around with 'flu' doesn't have it! When I woke that 1st time I couldn't open my eyes as the light was too bright; I didn't think that I was running a temperature, however; I could hardly move, DH had to lift/carry me to the bathroom. My large joints ached, fortunately not all at the same time: Knees, hips, ankles, shoulders. 12 months later when I woke I knew what it was. Both nights I had gone to bed feeling OK!
Yes occasionally people will react to vaccines. This is a personal choice to have/not, but 'flu can be awful for any1 health compromised.