A Study of mRNA-1018 Pandemic Influenza Candidate Vaccines in Healthy Adults

Key Inclusion Criteria:

• Healthy as determined by medical evaluation including medical history, physicalexamination, laboratory tests, and results of electrocardiogram testing.

• Body mass index of 18 kilograms (kg)/square meter (m^2) to 39 kg/m^2 (inclusive) atthe Screening visit.

• For female participants of childbearing potential: negative pregnancy test, adequatecontraception, and not currently breastfeeding.

Key Exclusion Criteria:

• Participant is acutely ill or febrile (body temperature ≥ 38.0 degrees Celsius [°C]/100.4 degrees Fahrenheit [°F]) 72 hours prior to or at the Screening Visit orDay 1.

• History of a diagnosis or condition that, in the judgment of the Investigator, isclinically unstable or may affect participant safety, assessment of safetyendpoints, assessment of immune response, or adherence to study procedures.

• Any medical, psychiatric, or occupational condition, including reported history ofsubstance abuse, that, in the opinion of the Investigator, might pose additionalrisk due to participation in the study or could interfere with the interpretation ofstudy results.

• Participant has received systemic immunosuppressants or immune-modifying drugs for >14 days in total within 180 days prior to Screening Visit (for corticosteroids ≥10milligrams [mg]/day of prednisone equivalent) or is anticipating the need forimmunosuppressive treatment at any time during participation in the study.

• Participant has received any vaccine authorized or approved by local health agencyincluding mRNA vaccine ≤28 days prior to study intervention (Day 1) or plans toreceive a vaccine authorized or approved by local health agency within 28 daysbefore or after the study intervention.

• Participant has participated in an interventional clinical study within 28 daysprior to the Screening visit based on the medical history interview or plans to doso while participating in this study.

Other inclusion/exclusion criteria may apply.