I don't have particularly strong feelings about flu vaccinations but I did have an interesting experience recently that is related, and which really illustrates one of the fundamental problems with human thought.
So my wife got herself vaccinated which makes a ton of sense - she works for a branch of the government that deals with preventative health stuff on reserves. They constantly have people on and off reserves and so they get inoculated for EVERYTHING.
She was expecting some soreness and fatigue after the inoculation which also makes plenty of sense; that's very common.
The day after she got the shot, I got sick. Like totally sick. Halfway through my work day I was like, "okay, everyone, I'm driving home now, because I'd rather not puke a lot here in front of all of you. Back tomorrow!" Then I drove home with my window open because I doubted I'd be able to open it fast enough to not get my car full of puke. And the splashback would be awful if it got in your eyes.
It was incredibly hard to convince myself that these were unrelated. I had to look up all the symptoms of the flu and all the symptoms of food poisoning and all kinds of studies on contagion between vaccinated people and theoretical contagion with dead viruses and so on before I could get my brain to stop telling me that the whole thing was a coincidence.
Thankfully I didn't have any sort of dry cough or anything. But even so, man, the proximity of the shot and my illness was enough to make my brain set off all kinds of alarms and warnings and it was hard to shut it up.
So in the end I learned something: I get how the anti-vaccination people feel now. They're totally wrong, but I understand why that is so hard for them to accept. There is very obviously a potent mechanism in your brain (which I guess is there to help keep you from getting poisoned by foods, ironically) which links illness and recent events.
All in all an interesting experience. Aside from the horrible sickness which I just hated.