Not a flu shot but 4 days after getting the 2nd COVID vax for the variant before last (in the US) - this was in early July of last year. I woke up 4 days later with horrible pain and stiffness in my shoulders, clavicals and pelvic area. I thought it was yet another lifting injury and didn't explore other potential causes until PT failed to help. I self diagnosed and finally got in to see a rheumatologist to confirm, although my C-reactive and sed rate blookwork remains normal. I think mine was due to a confluence of events that caused my immune system to say enough. I got COVID in Aug '23 and had to take 2 rounds of Paxlovid to get rid of it, then I got a really bad ear infection that would not go away. I'm a lap swimmer so there was no way I was going to get a hole punched in my eardrum, so I was on just about every allergy drug there is for 9 months. The ear infection had just cleared in late June '24, when I got the jab and here I am.

One other thing, during the time I was suspicious of PMR but before officially being diagnosed, I got a flu shot. It knocked me down for 4 days. My rheumatologist told me no more vaxs until maybe this fall and that's if I can taper off prednisone... so fingers and toes crossed!

I hope you get better soon! Although it's a double edgeed sword, prednisone has been a lifesaver for me.