I am putting this here in a stand-alone document so that I can refer to it easily.
People have been asking me which booster they should get, Pfizer or Moderna? For effectiveness, the answer is always Moderna, though it’s not so bad if you get Pfizer. All the studies I have seen say that Moderna gives you slightly better protection, probably because the Moderna and Pfizer mRNAs are practically identical, but Moderna has more. (The Pfizer initial doses and booster doses have 30mg of mRNA; the Moderna initial doses have 100mg and the booster doses have 50mg.)
However, it’s also very clear that the differences in effectiveness are small and that you are better off with a booster than without.
For side effects, you will probably have fewer with Pfizer. (I’ve had the trifecta — AZ, Pfizer, and Moderna. AZ knocked me on my ass, Moderna made me not want to do ANYTHING, and Pfizer just felt like someone punched me in the arm.) There is a very slight risk of myocarditis if you are young (like under 30), but the risk is low. Not only that, the risk of a severe case of myocarditis is really low.
So if you are over 30, take Moderna if you have a choice. If all they have is Pfizer, take that and be happy, you’re still getting a good booster. If you are under 30, I probably would still recommend Moderna, but I can respect if you want to drive the myocarditis risk as low as you can because they are both good boosters.
Most of the studies have been in test tubes. To be fair, I think there was one study which found that on ONE measure (out of several, e.g. IgA, IgG, IgM, etc.), Pfizer was slightly better. Otherwise, Moderna does better in test tubes. Here are a few studies; alas none are new enough to look at levels against Omicron:
- A very recent US study
- This big study (COV-BOOST) only looked at Pfizer and AZ first doses
- (There are others, but I don’t have time right now to look. Later.)
There’s been one study in people (vs. in test tubes) that I can remember, and here are its graphs.
For two doses of Pfizer plus a booster, Moderna is more clearly better.
With two doses of Moderna, the advantage of a Moderna booster is smaller (probably because they got about three times as much mRNA as people with two initial doses of Pfizer):
For protection against hospitalization, that study didn’t have any data for two Moderna doses to start. Here’s the chart for protection against hospitalization for people who started with two Pfizers:
Again, Moderna is better, but again, it’s small compared to the benefit of getting ANY third dose.