Study to Evaluate the Safety, Reactogenicity, and Immunogenicity of mRNA-1403 and mRNA-1405 to Prevent Norovirus Acute Gastroenteritis in Healthy Adults 18 to 80 Years of Age

Key Inclusion Criteria:

- Phase 1 Part: Adults 18 to 49 years of age at the time of consent or adults 60 to 80
years of age at the time of consent.

- Phase 2 Part: Adults 18 to 80 years of age at the time of consent.

- Body mass index of 18 to 39 kilogram/meter^2 (inclusive) at the Screening Visit.

- Participants assigned female at birth are eligible to participate if they are not
pregnant or breast/chest/body feeding.

- A person of childbearing potential is using a highly effective contraceptive method.

- Participant has provided written informed consent for participation in this study,

Key Exclusion Criteria:

- Is acutely ill or febrile (temperature ≥38.0°C [100.4°F]) 72 hours prior to or at
the Screening Visit or Day 1

- History of a diagnosis or condition that, in the judgment of the Investigator, is
clinically unstable or may affect participant safety, assessment of safety
endpoints, assessment of immune response, or adherence to study procedures.

- Has a medical, psychiatric, or occupational condition, including reported history of
substance abuse, that may pose additional risk as a result of participation, or that
could interfere with safety assessments or interpretation of results according to
the Investigator's judgment.

- Has a current or previous diagnosis of immunosuppressive condition, to include human
immunodeficiency virus, or immune-mediated (autoimmune) disease that requires
immunosuppressive therapies (drugs or biologics). The use of topical corticosteroids
or other immunosuppressive agents (for example, topical calcineurin inhibitor) may
be eligible for participation at the discretion of the Investigator.

- History of anaphylaxis, urticaria, or other significant AR requiring medical
intervention after receipt of a vaccine or intervention that includes one or more of
the same components contained in the study vaccine.

- Any history of myocarditis or pericarditis.

- Coagulopathy or bleeding disorder considered a contraindication to IM injection or
phlebotomy.

- Dermatologic conditions that could affect local solicited AR assessments (for
example, tattoos, psoriasis patches affecting skin over the deltoid areas).

- Has received systemic immunosuppressive therapies (drugs or biologics) for >14 days
in total within 6 months prior to Screening (for corticosteroids ≥10 mg/day of
prednisone equivalent) or is anticipating the need for immunosuppressive treatment
at any time during participation in the study. Inhaled, nasal, intra-articular, and
topical steroids are allowed.

- Has received or plans to receive any licensed/authorized vaccine (to include severe
acute respiratory syndrome-related coronavirus-2 vaccine) ≤28 days prior to or
within 28 days after each study intervention, with the exception of influenza
vaccines, which may be given 14 days before or after receipt of a study
intervention.

- Has received systemic immunoglobulins or blood products within 3 months prior to the
Screening Visit or plans for receipt during the study.

- Has donated protocol-specified volume of blood products within protocol-specified
timeframe.

- Participated or plans to participate in an interventional clinical study within
protocol-specified timeframe.

- Phase 2 Part: Individuals who are participating/have participated in the Phase 1
part of the study are excluded.

- Phase 1 Part: Any individual with laboratory abnormalities achieving thresholds
defined in the protocol.