I am a 63 year old postmenopausal woman with no history of anemia. After 2 doses of the Moderna vaccine (and possible asymptomatic covid, or I may have had covid before the vaccines also) within 2 months I began to experience difficulty exercising (ie would have to stop and catch my breath every 10 minutes, extreme thirst, dizziness when I bent over. Being able to only climb 2 flights of stairs without stopping (at sea level, I live at 4 thousand feet) difficulty hiking at altitude or sea level, etc. Then came ski season (9 to 10,000 feet) and I could barely make it down the hill.
Needless to say, I went to the doctor for a bunch of tests, if I would have gotten the blood done first that would have told the problem, I was severely anemic. Of course if you are anemic with no obvious cause they assume it is GI tract bleeding (which I was sure I didn't have anyway) so sent me off for upper and lower GI, NO BLEEDING.
All things being equal, same diet, etc. I think either the covid or the vaccine or both caused the anemia, lacking any other symptoms.
Of course, I have been hearing the same stuff as in this thread ie oh no we haven't heard of that. I am sure that both Covid 19 and the vaccines have a whole lot of effects we haven't heard of yet.