A Study to Investigate the Immunogenicity, Reactogenicity, and Safety of mRNA-1083 (Influenza and COVID-19) Vaccine in Adults ≥18 to <65 Years of Age

Inclusion Criteria:

• Medically stable.

• Participants who could become pregnant: negative pregnancy test and contraceptionfor at least 28 days prior to Day 1 and for at least 90 days after the studyintervention administration.

• Have received ≥2 coronavirus disease 2019 (COVID-19) vaccines, with the lastCOVID-19 vaccine administered >150 days prior to Day 1.

Exclusion Criteria:

• History of a diagnosis or condition that is clinically unstable or may affectparticipant safety, assessment of study endpoints, assessment of immune response, oradherence to study procedures.

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

• History of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infectionwithin 150 days prior to Day 1.

• Received systemic immunosuppressive treatment, including long-acting biologicaltherapies that affect immune responses (eg, infliximab), within 180 days prior toDay 1 or plans to do so during the study.

• Received or plans to receive any vaccine authorized or approved by a local healthagency within 28 days prior to Day 1 or plans to do so within 28 days post studyinjection.

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

• Received a licensed/authorized COVID-19 vaccine within 150 days prior to Day 1.

• Received any investigational influenza vaccine, investigational COVID-19 vaccine, orinvestigational combination vaccine for influenza and COVID-19 within 12 monthsprior to Day 1.

• Participated in a clinical study with investigational treatment within 90 days priorto Day 1 (Baseline).

Other protocol-defined inclusion/exclusion criteria may apply.