I had the Moderna vaccine and had enough of a decrease in my iron that I needed an infusion. My iron levels and RBC counts went down dramatically. Up until the vaccine I was donating blood to keep my hemocrit below 50 (I get testosterone which can cause this). When I had the blood test that showed my iron levels were below normal I was completely shocked. Now, I'm 8 months after my last Moderna dose, and my RBC and hemocrit are back up. Seems too coincidental to me that this happened when I had the COVID-19 vaccine.