Seems you have done really well in having the PMR only stick around for under 12 months. That is quite a short period for this illness. I had a flu shot in July 2023 (southern hemisphere) and within 2 days was in intense pain across the shoulders, front and back, The inflammatory markers escalated rapidly and I could hardly get out of bed. The flu vaccine as a trigger is documented in the research literature, although considered to be a rare side effect of that vaccine. I am still battling with PMR and occasionally have to go up to 20 mgs daily of steroids to get the inflammatory markers back to normal. The rheumatologist did say that the markers were quite volatile. So steering clear of flu vaccines and Covid boosters at this stage (although I had 5 prior to PMR) .