Fig. 1: Participant flow through the mRNA-1273 booster and mRNA-1273 variant booster cohorts.

In the mRNA-1273 booster phase, 20 participants who had received two injections of 100-μg mRNA-1273 completed the blinded phase and who went on to receive a single booster dose of 50-μg mRNA-1273 were selected for this preliminary analysis, with selection based on completion of day 15 visit assessments and immunogenicity sample availability. In the mRNA-1273 variant booster phase, enrollment was site specific and was based on predefined inclusion/exclusion criteria. Administration of booster doses occurred in a sequential manner (mRNA-1273 variant booster phase, which included the mRNA-1273.351 (50 µg) cohort; the mRNA-1273.211 (50 µg) cohort; and the mRNA-1273.351 (20 µg) cohort). aUnblinded or not unblinded to assigned treatment in the blinded portion of the phase 2a mRNA-1273 trial. bFifteen participants declined to receive a booster. cThirteen participants declined to receive a booster. dTwenty-two participants declined to receive an mRNA-1273 primary vaccination.