A Study of mRNA-1020 and mRNA-1030 Seasonal Influenza Vaccines in Healthy Adults

Phase 1/2, Randomized, Observer-Blind, Dose-Ranging Study to Evaluate the Safety, Reactogenicity, and Immunogenicity of mRNA-1020 and mRNA-1030 Candidate Seasonal Influenza Vaccines in Healthy Adults

The primary objective of this study is to evaluate the safety, reactogenicity, and humoral immunogenicity of mRNA-1020, mRNA-1030, and mRNA-1010 vaccines against vaccine-matched influenza A and B strains.

Inclusion Criteria:

• Body mass index of 18 kilograms (kg)/square meter (m^2) to 35 kg/m^2 (inclusive) at the Screening Visit.
• For female participants of childbearing potential: negative pregnancy test, adequate contraception or has abstained from all activities that could result in pregnancy for at least 28 days prior to Day 1, agreement to continue adequate contraception through 90 days following vaccine administration, and not currently breastfeeding.

Exclusion Criteria:

• Participant has had close contact to someone with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection or COVID-19 as defined by the Centers for Disease Control and Prevention (CDC) or has had a positive SARS-CoV-2 test in the past 10 days prior to the Screening Visit.
• Participant is acutely ill or febrile (temperature ≥38.0 degrees Celsius [°C]/100.4 degrees Fahrenheit [°F]) 72 hours prior to or at the Screening Visit or Day 1.
• Any medical, psychiatric, or occupational condition, including reported history of substance abuse, that, in the opinion of the Investigator, might pose additional risk due to participation in the study or could interfere with the interpretation of study results.
• Participant has received systemic immunosuppressants or immune-modifying drugs for >14 days in total within 180 days prior to screening (for corticosteroids ≥10 milligrams [mg]/day of prednisone equivalent) or is anticipating the need for immunosuppressive treatment at any time during participation in the study.
• Participant has received or plans to receive any licensed or authorized vaccine, including COVID-19 vaccines, ≤28 days prior to the study injection (Day 1) or plans to receive a licensed or authorized vaccine within 28 days after the study injection.
• Participant has received a Northern Hemisphere (NH) 2021-2022 seasonal influenza vaccine or any other influenza vaccine within 180 days prior to Day 1.
• Participant tested positive for influenza by CDC-recommended testing methods within 180 days prior to Day 1.
• Participant has donated ≥450 milliliters (mL) of blood products within 28 days prior to the Screening Visit or plans to donate blood products during the study.

Note: Other inclusion/exclusion criteria may apply.