As our pharmacist friend explained to us, The first dose and second dose of your Pfizer or Moderna COVID-19 vaccine should be exactly the same, both chemically and from a dosage standpoint. The third dose is also the same. She also told us there is no reason to wait, as long as you are past the original waiting period for each type of shot. My wire falls into the compromised category, so that’s why we both able to get the 3rd shot. But, if you are not, there are always ways around it, if you really want to get it now.