A Study of mRNA-1083 (SARS-CoV-2 and Influenza) Vaccine in Healthy Adult Participants, ≥50 Years of Age

Key Inclusion Criteria:

• Healthy adults either ≥65 years of age (Cohort A) or 50 to <65 years of age (CohortB) at the time of consent (Screening Visit).

• For female participants of childbearing potential: negative pregnancy test, adequatecontraception or has abstained from all activities that could result in pregnancyfor at least 28 days prior to Day 1, and agreement to continue adequatecontraception through 3 months following vaccine administration.

• Fully vaccinated for COVID-19 primary series according to the locally authorized orapproved regimen, and their last COVID-19 vaccine (primary series or booster) was ≥90 days prior to Day 1.

Exclusion Criteria:

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

• Any medical, psychiatric, or occupational condition, including reported history ofdrug or alcohol abuse, that, in the opinion of the Investigator, might poseadditional risk due to participation in the study or could interfere with theinterpretation of study results.

• Participant has received systemic immunosuppressants for >14 days in total within 180 days prior to Day 1 (for corticosteroids, ≥10 milligrams [mg]/day of prednisoneor equivalent) or is anticipating the need for systemic immunosuppressive treatmentat any time during participation in the study. Inhaled nasal and topical steroidsare allowed.

• Received or plans to receive any vaccine authorized or approved by a local healthagency ≤28 days prior to study injections or plans to receive a vaccine authorizedor approved by a local health agency within 28 days after the study injections.

• Received a seasonal influenza vaccine ≤150 days prior to Day 1.

• Tested positive for influenza by local health authority-approved testing methods ≤150 days prior to Day 1.

• Has had close contact to someone with COVID-19 as defined by the Centers for DiseaseControl and Prevention (CDC) in the past 10 days prior to Day 1.

• Has donated ≥450 milliliters (mL) of blood products within 28 days prior to theScreening Visit or plans to donate blood products during the study.

Note: Other protocol-defined inclusion/exclusion criteria may apply.