A Study on the Safety and Immunogenicity of Hexavalent Influenza mRNA Vaccine in Adult Participants 50 Years of Age and Older

Inclusion Criteria:

• Participant aged 50 years on the day of inclusion

• A female participant is eligible to participate if she is not pregnant orbreastfeeding and one of the following conditions applies:

• Is of non-childbearing potential. To be considered of non-childbearingpotential, a female must be postmenopausal for at least 1 year, or surgicallysterile.

OR

• Is of childbearing potential and agrees to use an effective contraceptive method orabstinence from at least 4 weeks prior to study intervention administration until atleast 12 weeks after study intervention administration.

A female participant of childbearing potential must have a negative highly sensitive pregnancy test (urine or serum as required by local regulation) within 8 hours prior to administration of study intervention.

Exclusion Criteria:

Participants are not eligible for the study if any of the following criteria are met:

• Known or suspected congenital or acquired immunodeficiency; or receipt ofimmunosuppressive therapy, such as anti-cancer chemotherapy or radiation therapy,within the preceding 6 months; or long-term systemic corticosteroid therapy (prednisone or equivalent for more than 2 consecutive weeks within the past 3months)

• Known systemic hypersensitivity to any of the study intervention components (eg,polyethylene glycol, polysorbate); history of a life-threatening reaction to thestudy interventions used in the study or to a product containing any of the samesubstances; any allergic reaction (eg, anaphylaxis) after administration of mRNAvaccine

• Previous history of myocarditis, pericarditis, and/or myopericarditis

• Known history of previous episodes of Guillain-Barré syndrome, neuritis (includingBell's palsy), convulsions, encephalitis, transverse myelitis, and vasculitis

• Participants with an electrocardiogram that is consistent with possible myocarditisor pericarditis or, in the opinion of the investigator, demonstrates clinicallyrelevant abnormalities that may affect participant safety or study results

• Self-reported thrombocytopenia, contraindicating intramuscular (IM) vaccinationbased on Investigator's judgment

• Bleeding disorder, or receipt of anticoagulants in the 3 weeks preceding inclusion,contraindicating IM vaccination based on Investigator's judgment

• Chronic illness that, in the opinion of the Investigator, is at a stage where itmight interfere with study conduct or completion

• Moderate or severe acute illness / infection (according to investigator's judgement)or febrile illness (temperature ≥ 38.0°C [≥ 100.4°F]) on the day of vaccination. Aprospective participant should not be included in the study until the condition hasresolved or the febrile event has subsided.

• Alcohol, prescription drug, or substance abuse that, in the opinion of theInvestigator, might interfere with the study conduct or completion

• Participant who had acute infectious symptoms or a positive SARS-CoV-2 RT-PCR orantigen test in the past 10 days prior to the first visit (V01)

• Receipt of any vaccine in the 4 weeks preceding study intervention administration orplanned receipt of any vaccine in the 4 weeks following study interventionadministration

• Receipt of immune globulins, blood or blood-derived products in the past 3 months

• Previous vaccination against influenza in the previous 6 months with aninvestigational or marketed vaccine

• Receipt of any mRNA vaccine/product in the 2 months preceding study interventionadministration or planned receipt of any mRNA vaccine in the 2 months after studyvaccination

• Participation at the time of study enrollment (or in the 4 weeks preceding studyintervention administration) or planned participation during the present studyperiod in another clinical study investigating a vaccine, drug, medical device, ormedical procedure

• Self-reported or documented seropositivity for human immunodeficiency virus,hepatitis B virus, or hepatitis C virus