The duration of each participant's participation is 12 months for the Sentinel and Main Cohorts and 24 months overall for the subset of participants enrolled in the Booster Cohort.~Treatment Duration:~Sentinel Cohort: 1 intra-muscular (IM) injection. Participants will be followed for 12 months post-vaccination.~Main Cohort: 1 IM injection. Participants will be followed for 12 months post-vaccination.~Booster Cohort: 1 IM injection 12 months after the primary vaccination. Participants will be followed for 12 months after administration of the booster dose.
The purpose of this study is to assess the safety and immunogenicity of a single intramuscular (IM) injection of 3 dose-levels of a respiratory syncytial virus (RSV) messenger ribonucleic acid (mRNA) vaccine candidate formulated with 2 different lipid nanoparticles (LNPs) (ie, LNP containing CL-0059 or CL-0137) in healthy adult participants aged between 18 and 50 years, and 60 years and older. The primary objectives of this study are to assess the safety and immunogenicity profiles across the dose-level groups (low, medium, and high doses) with 2 LNPs (CL-0059 and CL-0137). In addition, the study will evaluate the safety and immunogenicity of a booster vaccination administered 12 months after the primary vaccination in a subset of the study population. The duration of each participant's participation is 12 months for the Sentinel and Main Cohorts and 24 months overall for the subset of participants enrolled in the Booster Cohort.