Figure 3. Secondary Analyses of Efficacy.

Vaccine efficacy was calculated as 1 minus the ratio of the incidence of SARS-CoV-2 infection per 1000 person-years (mRNA-1273 vs. placebo). The primary definition of Covid-19 was at least two systemic symptoms or at least one respiratory symptom plus at least one nasopharyngeal swab, nasal swab, or saliva sample that was positive for SARS-CoV-2 by RT-PCR. The secondary case definition of Covid-19 was at least one systemic or respiratory symptom plus a swab that was positive for SARS-CoV-2 by RT-PCR. The category of SARS-CoV-2 infection (regardless of symptoms) was defined as a combination of postbaseline symptomatic Covid-19 and asymptomatic SARS-CoV-2 infection in participants with a negative SARS-CoV-2 status at baseline. Asymptomatic SARS-CoV-2 infection was defined as the absence of symptoms and infections detected by a postbaseline positive RT-PCR or serologic test in participants with a negative SARS-CoV-2 status at baseline. The per-protocol (PP) population consisted of all participants who had received at least one injection of mRNA-1273 or placebo and 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; this population included 1042 participants in the placebo group and 2139 participants in the mRNA-1273 group. The modified intention-to-treat population with the exclusion of those who had received the incorrect injection (mITT1) consisted of all participants who had no serologic or virologic evidence of previous SARS-CoV-2 infection before the first injection of mRNA-1273 or placebo (both a negative RT-PCR test for SARS-CoV-2 and a negative serologic test based on binding antibodies specific to SARS-CoV-2 nucleocapsid at baseline; this population included 1073 participants in the placebo group and 2163 participants in the mRNA-1273 group. NE denotes not estimated.