This study was a multi-site, Phase I/II, open-label, dose-escalation study. The study included the first in human dose and dose ranging groups in healthy younger participants (aged 18 to 55 years [yrs]) and older participants (aged 56 to 85 yrs). The conducted Part A followed a dose escalation design. Discretionary dose de-escalation and refinement was also planned. Study participants with the first-in-human [FIH] immunization and any subsequent dose escalation cohorts were immunized using a sentinel dosing/subject staggering. For any dose de-escalation or dose-refinement cohorts in younger adults, i.e., cohorts with doses lower than previously tested, participants were dosed using a subject staggering process. Cohorts in older participants were optional and dependent on acceptability of dosing in younger participants. Part A consisted of a treatment phase (screening to Visit 7) and a follow-up phase (Visits 8 to 10).
Originally, the study was planned to include two parts, i.e., Part A and Part B, however Part B was skipped due to changes in the overall clinical development plan. The conducted Part A was a dose-finding part to investigate the optimal dose, allowing dose adjustments upwards and downwards in younger participants. Doses tested in older participants were chosen based on acceptability of dosing in younger participants.