Phase 1/2 Study of Respiratory Syncytial Virus and Human Metapneumovirus (RSV+HMPV) Vaccine Candidate in Adults 60 Years of Age and Older

This study is a Phase 1/2, randomized, observer-blind, active and placebo-controlled, multi-center study to be conducted in approximately 2400 adults 60 years of age and older. The aim of the study is to evaluate the immunogenicity and safety of an RSV+HMPV vaccine candidate for the prevention of RSV and HMPV disease among adults 60 years of age and older. While there are 3 FDA approved/licensed RSV vaccines currently available to the public, no vaccine is available for the prevention of HMPV in older adults. This study is intended to provide data in support of further clinical development of the RSV+HMPV vaccine candidate. The study will consist of 4 cohorts and 11 vaccine groups (RSV+HMPV \[6 dose levels\], placebo and 4 control groups). The duration of the study will be approximately 12 months for each participant.

Inclusion Criteria: * Aged 60 years or older on the day of inclusion * Non-childbearing potential (ie, post-menopausal for at least 1 year or surgically sterile) Exclusion Criteria: * History of laboratory-confirmed RSV and/or laboratory-confirmed HMPV infection affecting the participant and/or the participant's household in the previous 12 months * Previous history of myocarditis, pericarditis, and/or myopericarditis * Screening electrocardiogram (ECG) that is consistent with possible myocarditis, pericarditis, and/or myopericarditis or, in the opinion of the investigator, demonstrates clinically relevant abnormalities that may affect participant safety or study results * Chronic illness that, in the opinion of the investigator, is at a stage where it might interfere with study conduct or completion * Previous history of Guillain-Barré Syndrome * Any vaccine given 4 weeks before or 4 weeks after study intervention * Previous vaccination against RSV and/or HMPV with an investigational or marketed vaccine * Receipt of any mRNA vaccine/product in the 2 months preceding study intervention administration * Has received a blood transfusion or blood-derived products, including immunoglobulins, in the past 3 months * Any screening laboratory parameter with laboratory abnormality \> Grade 1 or deemed clinically significant by the investigator; if deemed appropriate, investigator may repeat these assessments The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.