I, too, have had an iron issue (low ferritin as well) under the same circumstances: one Moderna shot, followed by Covid. There is a lot of anecdotal evidence out there regarding low iron post-vaccination, even when there has been no Covid, so it's difficult to say which is the culprit. In my case (a few months later), my hair was breaking off 1-2" from my scalp, and my nails became soft, which sent me to the doctor. With 350-mg of Ferrous Sulphate daily for more than one year, my levels were brought back into the "normal" zone but still not where I'd like them to be. My suggestion is to have your blood checked for iron and ferritin levels; you, too, may need to take iron.