from what I understand it matters but I don't know if there is science to base that on...Moderna seems to have better chance of fending off Delta but there seems to be no statistical difference in hospitalizations (which is the most important criteria to me)...that being said there is now a study showing that a second injection with JandJ make it is as efficacious as either of the mRNA vaccinesDoes it have to be the same type? Seems Moderna may now have better results than Pfizer.
At the end of the day I would talk to your physician before jumping from one to the other