My understanding is that the Moderna has more of the active mrna agent in it.
This made me curious about the boosters, so I googled it. I believe you are correct:
>>>If you had Moderna for your first two shots, Poland says, you might consider getting the
Pfizer booster because it's a smaller dose (30 micrograms) than the Moderna booster (50 micrograms). This could conceivably cut down on side effects, Poland says, while still providing a very strong immune response. He says he plans to do just this for his booster. It's also possible, some experts say, that people who had the Pfizer shots initially will want to chase them with the Moderna booster precisely because the Moderna dose is higher than Pfizer's — with the idea that this might produce a bigger boost in antibodies.<<<
Editorial comment: Referring to the booster as a chaser shot does make it more appealing! (I suppose one could have Corona followed by a Moderna chaser shot?)
You've seen the headlines about COVID boosters. But what does it all mean for you? Here's how to sort through the science and figure out if and when you need a booster and which one to get.
www.npr.org
Here are the mRNA doses in the first two Pfizer and Moderna shots:
>>>Each dose of the Pfizer/BioNTech vaccine delivers 30 µg of mRNA, while each of Moderna’s contains 100 µg.<<<
https://www.the-scientist.com/news-opinion/moderna-vs-pfizer-is-there-a-best-mrna-vaccine-69229
Assuming these reports are accurate, the Pfizer booster has the same amount of mRNA as the first two Pfizer shots, but the Moderna booster has one-half of the first two Moderna shots.
Assuming I'm eligible for a booster at some point, I'm going to try to get the Moderna booster (my first two were Pfizer) on the theory that more is always better (carrying over my approach to subwoofers), but I do wonder if 50 vs 30 micrograms really makes much difference.