This thread is old, but there is evidence the vaccines can cause or make worse various types of blood disorders including anemias. People aren't posting to VAERS because their doctors are refusing to admit there may be a link between the vaccine and anemia. All things being equal, my ability to exercise and my endurance levels went steadily down after I got the second Moderna shot, I am 63 years old so always wonder if I am just getting old. When I got Covid 9 months later (in spite of being vaccinated) my energy level and my ability to exercise at altitude (I live in the mountains) went to the lowest level ever. Finally I was diagnosed with anemia (my hemoglobin was at 7.9). I have had all the GI tests for bleeding, none detected.