Statistical Analysis
EVENT
The exposed set included all participants who received at least 1 dose of a study vaccine. The per-protocol set (PPS) included study participants who met eligibility criteria, received all vaccinations according to their random assignment, complied with protocol-defined procedures, did not receive prohibited medications or vaccines, had available postvaccination immunogenicity data, and where the administration site was known.Anti-gE antibody concentrations and anti–S protein antibody concentrations were expressed as between-group ratios of the geometric mean concentration (GMC) 1 month post-RZV2 and 1 month post–mRNA-1273 booster, respectively. The 95% confidence intervals (CIs) of the between-group GMC ratios were computed using an analysis of covariance model on the logGMCs were calculated by taking the anti-log of the mean of the log concentration transformations. Noninferiority of the anti-gE antibody or anti-S antibody response was demonstrated if the upper limit of the 95% CI of the adjusted GMC ratio (Seq over Coad) was <1.5, 1 month post-RZV2 or post–mRNA-1273 booster, respectively.Assuming a GMC ratio of 1.1 between the Seq and Coad groups, the global power to meet both co-primary objectives with 245 evaluable participants in the Seq and Coad groups was 90%. Assuming that about 10% of the randomized participants would not be evaluable, approximately 546 participants (273 in each study group) were planned.Descriptive immunogenicity analyses were also performed. A vaccine response following RZV was defined as a participant who had at least a 4-fold greater anti-gE antibody concentration post-RZV2 compared to prevaccination for initially seropositive participants, or compared to the antibody cutoff value (97 mIU/mL) for participants who were seronegative at prevaccination.Mean geometric increase (MGI) was defined as the within-participant ratios of the postvaccination to the prevaccination antibody concentration, thereby representing fold-rise in antibody concentration.Safety was evaluated descriptively, without predefined statistical criteria. For solicited systemic AEs, the frequency of occurrence of any event in the sequential group was calculated by counting whether the event occurred following mRNA-1273 or following RZV1 administered 2 weeks later. If a participant had the same event after both mRNA-1273 and RZV1, it was counted only once at maximum severity.All statistical analyses were performed using SAS version 9.4 software.