The Pfizer and Moderna are ( simply speaking ) essentially the same, containing synthetic RNA. where they are different is dosage. Pfizer 0.3ml x2
Moderna .05 x2 The Moderna being a significantly higher dose with an arguably stronger antibody response. It was withdrawn from use in some European countries for younger age groups over concerns about rates of myocarditis. I did my research, more than most, went in eyes wide open. In the end there is nothing stronger than personal experience. If you didn't have adverse reaction the vaccine the first rounds, that's great but maybe consider what may happen the 4th and 5th time etc. Booster intervals in some countries are being reduced to 3months.
