A Study to Learn About a Modified RNA Vaccine Against Shingles in Healthy Adults

The purpose of this clinical study is to learn about the safety, extent of the side effects (reaction to vaccine), and immune response (your immune system's reaction) of the study vaccine called Varicella Zoster Virus modRNA (VZV modRNA). We are seeking for healthy participants 50 through 85 years of age. This study will be conducted in 2 substudies: Substudy A (Phase 1) and Substudy B (Phase 2). Substudy A: This substudy is the Phase 1 portion of the study. In this substudy, participants will receive 1 of 3 VZV modRNA vaccine candidates (different construct, different dose levels and different formulation \[frozen or freeze dry powder\]) or the approved shingles vaccine intramuscularly. Participants will be assigned in 1 of 10 groups in the study. Vaccination will be given either as a 2-dose series using one of two dosing schedules (either 2-months apart or 6-months apart), or (in one of the groups), as a single VZV modRNA vaccine at the first vaccination visit and saline at the second vaccination visit. Participants will take part in this study for 8 to 12 months depending on the group they are assigned to. Some group(s) will continue into persistence-of-immunity (overtime assessment of effect of vaccine) portion of the study. Those participants assigned to these selected groups will be involved in the study for up to 5 years. Substudy B: This substudy is the Phase 2 portion of the study. In this part of the study, participants will receive either VZV modRNA vaccine at selected dose level/schedule/formulation or approved shingles vaccine. This selection was determined from data collected in Substudy A. Participants will be involved in this study for up to 5 years.