a safety, tolerability, and immunogenicity study of mrna-1345 and mrna-1365 in participants aged 5 months to <24 months

Conditions: Respiratory Syncytial Virus; Human Metapneumovirus

Summary: the purpose of this study is to assess the safety and immunogenicity of mrna-1365, an mrna vaccine targeting respiratory syncytial virus (rsv) and human metapneumovirus (hmpv) and mrna-1345, an mrna vaccine targeting rsv, in participants aged 5 months to \<24 months.


Eligibility criteria:
inclusion criteria: * the participant is 8 months to \<24 months (part a), 5 months to \<8 months (part b), or 8 months to \<12 months (part c) of age at the time of randomization (day 1/baseline visit), who is in good general health, in the opinion of the investigator, based on review of medical history and screening physical examination. * in the investigator's opinion, the parent(s)/ legally authorized representative (lar)(s) understand and are willing and physically able to comply with protocol-mandated follow up, including all procedures, and provide written informed consent. * the participant is growing normally for age in the opinion of the site clinician in the months prior to enrollment. * the participant was born at full-term (≥37 weeks gestation) with a minimum birth weight of 2.5 kilograms (kg). * for part c cohort 7: participant must have received nirsevimab ≥6 months prior to day 1 visit. * for part c cohort 8: participant was eligible at any time since birth, according to national guidelines, to receive nirsevimab prior to day 1 visit but did not do so. exclusion criteria: * has a known history of symptomatic rsv (part a: within 3 months; part b and part c: since birth) or hmpv infection (part a: within 3 months; part b: since birth) prior to administration of the first dose of investigational product (ip) or has a known close contact with anyone with laboratory-confirmed rsv (parts a, b, and c) or hmpv infection (parts a or b) within 14 days prior to administration of the first dose of ip. * is acutely ill or febrile 24 hours prior to or at the screening visit. fever is defined as a body temperature ≥38.0°celsius/≥100.4°fahrenheit. participants who meet this criterion may have visits rescheduled within the relevant study visit windows. * has previously been administered an investigational or approved vaccine for prevention of rsv (parts a, b, and c) or hmpv (parts a and b) infection or if the participant's mother received an investigational or approved vaccine for the prevention of rsv (parts a, b, and c) or hmpv (parts a and b) infection during pregnancy. * has received investigational or approved agents for prophylaxis against rsv or hmpv (for example, monoclonal antibodies) or is intending to receive these during the course of the study. for part c (cohort 7 only), use of nirsevimab ≥6 months before day 1 visit is allowed. * has a known hypersensitivity to a component of the vaccine or its excipients. hypersensitivity includes, but is not limited to, anaphylaxis or immediate allergic reaction of any severity to a previous dose of an mrna vaccine or any of its components (including polyethylene glycol or immediate allergic reaction of any severity to polysorbate). * has a medical condition that, according to the investigator's judgment, may pose additional risk as a result of participation, interfere with safety assessments, or interfere with interpretation of results. note: other protocol-defined inclusion/exclusion criteria apply.

Keywords: mrna-1345 mrna-1365 rsv vaccine hmpv vaccine rsv/hmpv vaccine