The boosters are to be given at least six months after a person’s second dose and, according to Moderna, can be used for mix-and-match boosting. That is, people who received two Pfizer-BioNTech vaccine doses earlier this year could get a Moderna booster and vice versa.
Preliminary data released last month from a mix-and-match booster trial run by the National Institutes of Health found that Moderna boosters appeared to generate the highest antibody levels overall, including in people who had previously received two doses of the Pfizer-BioNTech vaccine. However, the trial used a full dose of the Moderna vaccine (100 micrograms) for a booster, whereas the FDA has authorized a half-dose shot (50 micrograms) for boosters. It’s unclear if the half dose offers the same edge over boosting with a third Pfizer-BioNTech shot, which is given at the same dosage as the first two shots (30 micrograms).