@bulper It's well documented in the research that flu vaccine (likely the adjuvants used) can trigger PMR in some people. And similar research has been emerging in relation to covid vaccines.

"Trigger" is the essential word as it is likely that a set of predisposing factors, etc are also involved: e.g. genetics (Northern European background), age and recent bacterial or viral infection. But a fundamental understanding of exactly what causes PMR is still unknown. In my case the flu vaccine was certainly a major trigger, with a very aggressive inflammatory response and CRP rising to 178 within 48 hours and muscular pain (shoulder and hip girdles) that was like being sliced with razor blades. A barrage of tests ruled everything else out before PMR was diagnosed, and I have now had it for 2 years. I am certainly not anti-vaccine but I wish that I had been alerted to the fact that I was in a high risk category for PMR at the time the vaccine was administered.