The vaccines have differed in their dosing schedules too. Vaccinated (and un-boosted) Americans have received 60 micrograms of Pfizer over a period of three weeks, 200 micrograms of Moderna over four weeks, or 50 billion particles of J&J in one sitting. It’s apples and oranges, except you have to wolf down the apple all at once, and some of the oranges are tangerines, and you can eat only a few slices at a time.

Even the one-week difference between Pfizer’s schedule and Moderna’s could be important. Mark Slifka, an immunologist at Oregon Health and Science University, told me that it could play into Moderna’s slightly longer-lasting protection. Angela Rasmussen, a virologist at the University of Saskatchewan’s Vaccine and Infectious Disease Organization, pointed out that the AstraZeneca vaccine—an adenovirus-vector design like J&J’s—also seems to provide more protection when its doses are spaced further apart.

The number of vaccine doses you receive also matters, no matter their specific size and schedule. Slifka thinks that the number of times you get a vaccine is far more important than the amount of it delivered in each syringe. Getting more than one dose “is actually the great equalizer among vaccinations,” he said, because it teaches the immune system that a particular threat should be taken seriously. Having multiple rounds of a moderately sized dose may also be better than taking one megadose, because the more vaccine you get at once, the worse your side effects are likely to be. “With the mRNA vaccines and the adenovirus vectors, there’s an upper limit to how much you can give [in one dose] before it’s just not a good idea,” Slifka said.