A Study on the Safety and Immune Response of Investigational mRNA Seasonal Flu/COVID-19 Combination Vaccine in Adults

Inclusion Criteria: 1. Participants, who, in the opinion of the investigator, can and will comply with the requirements of the protocol independently or with the assistance of the caregiver. 2. Informed consent obtained from the participant prior to performance of any study-specific procedure. 3. A male or female 65 to 85 years of age (YoA) (inclusive) at the time of screening. 4. Healthy participants or medically stable patients as established by medical history and clinical examination. 5. Other protocol-defined inclusion criteria may apply. Exclusion Criteria: 1. Any clinically significant laboratory abnormality. 2. History of symptomatic influenza/ SARS-CoV-2 infection confirmed by local health authority-approved testing methods within 180 days (for influenza) or 90 days (SARS-CoV-2 infection) prior to study intervention administration. 3. History of Guillain-Barré syndrome (GBS) within 6 weeks of receiving any vaccine. 4. Current or past malignancy, unless completely resolved without clinically significant sequelae (e.g., no evidence of disease following successful treatment of basal cell carcinoma cases are allowed) for \>5 years. 5. Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history and physical examination (no laboratory testing required). 6. History of or current suspicion of myocarditis or pericarditis (including following administration of an mRNA vaccine); or idiopathic cardiomyopathy, or presence of any medical condition that increases the risk of myocarditis or pericarditis, including cocaine abuse, cardiomyopathy, endomyocardial fibrosis, hypereosinophilic syndrome, hypersensitivity myocarditis, eosinophilic granulomatosis with polyangiitis and persistent myocardial infection. 7. History of any reaction or hypersensitivity likely to be exacerbated by any component of the study intervention(s). 8. Acute or unstable chronic conditions, clinically significant pulmonary, cardiovascular, or renal functional abnormality, as determined by physical examination and/or laboratory screening tests. 9. History of hypersensitivity or allergic reaction to any previous influenza or COVID-19 vaccine. 10. History of hypersensitivity or allergic reaction to any previous mRNA vaccine. 11. Administration of any influenza vaccine within 181 days before the study intervention administration (Day -180 to Day 1) or planned administration within 28 days (Day 29) after the study intervention administration. 12. Administration of a SARS-CoV-2 antigen-containing vaccine in the period starting 91 days before the study intervention administration (Day -90 to Day 1) or planned administration within 28 days (Day 29) after the study intervention administration. 13. Administration of any mRNA-based vaccine in the period starting 29 days before the study intervention administration (Day -28 to Day 1) or planned administration within 28 days (Day 29) after the study intervention administration. 14. Administration of any other vaccine not foreseen by the study protocol in the period starting 29 days (Day -28 to Day 1) before the study intervention administration or planned administration within 28 days (Day 29) after the study intervention administration. 15. Other protocol-defined exclusion criteria may apply.