Figure 1. Randomization and Analysis Populations.

The full analysis population consisted of all participants who had undergone randomization and received at least one injection of mRNA-1273 or placebo; the per-protocol population consisted of all participants in the full analysis population who had received planned injections of mRNA-1273 or placebo, complied with the timing of the second injection, had no immunologic and virologic evidence of previous Covid-19 at baseline, and had no major protocol deviations; the modified intention-to-treat (mITT) population consisted of all participants in the full analysis population who had no serologic or virologic evidence of previous SARS-CoV-2 infection before the first injection (both a negative reverse-transcriptase–polymerase-chain-reaction [RT-PCR] test for SARS-CoV-2 and a negative serologic test based on binding antibodies specific to SARS-CoV-2 nucleocapsid) at baseline; the mITT1 population consisted of all participants in the mITT population with the exclusion of those who received the incorrect injection; and the safety population consisted of all participants who received at least one injection. The per-protocol immunogenicity subpopulation consisted of randomly selected participants who had received the planned injections of mRNA-1273 or placebo according to schedule, complied with the timing of the second injection, had no immunologic and virologic evidence of previous Covid-19 at baseline, complied with the immunogenicity testing schedule, and had no major protocol deviations that affected the key or critical data; participants who were seropositive at baseline were excluded from the per-protocol immunogenicity subpopulation. Two participants who received placebo did not receive the second injection and then discontinued the trial later for a reason listed as “other.” One participant who received mRNA-1273 did not receive the second injection and continued in the trial.