I never had PMR and barely any signs of arthritis until a few days after my first Moderna vaccine. My pain was also 7-9. Because I was in the 50-70 yr old age group, my primary thought it might be PMR so he put me on prednisone 20mg/2x day. It took a couple days to kick in but the pain was soon under control, went back for labs, found the inflammation high, and I was then referred to a rheumatologist who is watching my SED labs and advising me on tapering off the Prednisone.
When reading about PMR I learned that there is thought to be a connection to viruses and vaccinations — that was noticed before covid was a pandemic. It has also been noticed that it may be connected to people of Northern European or Scandinavian descent. Those were true for me.