I think these autoimmune diseases are a rare reaction to the covid vaccine, but I also was diagnosed with PMR after getting my second booster. No side effects at all from the first three shots. It's hard to know if you want to risk Covid or PMR. I'm glad I got the first three shots but I certainly don't want to risk another bout of PMR so probably won't get any more boosters, including a flu shot, at least not this year.