Study to Evaluate Safety and Immunogenicity of a Pandemic Flu H5 mRNA Vaccine in Healthy Adults Aged 18 Years and Older

Inclusion Criteria:

• Aged 18 years or older 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 or abstinence from at least 4 weeks prior to each study intervention administration until at least 12 weeks after the last study intervention administration.

• A female participant of childbearing potential must have a negative highly sensitivepregnancy test (urine or serum as required by local regulation) within 8 hoursbefore the first dose of study intervention.

Exclusion Criteria:

• 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 an mRNAvaccine .

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

• Known history of previous episodes of Guillain-Barré Syndrome (GBS), neuritis (including Bell's palsy), convulsions , encephalitis, transverse myelitis, andvasculitis.

• 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 IM injection based oninvestigator's judgment.

• Bleeding disorder, or receipt of anticoagulants in the 3 weeks preceding inclusion,contraindicating IM injection 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 judgment)or febrile illness (temperature ≥ 38.0°C [≥ 100.4°F]) on the day of studyintervention. A prospective participant should not be included in the study untilthe condition has resolved 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 severe acute respiratorysyndrome coronavirus 2 (SARS-CoV-2) reverse transcriptase polymerase chain reaction (RT PCR) or antigen test in the past 10 days prior to the first visit (V)01.

• Receipt of any vaccine other than an mRNA vaccine in the 4 weeks preceding studyintervention administration or planned receipt of any vaccine other than an mRNAvaccine in the 3 weeks following the second dose of the study intervention .

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

• 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 thesecond dose of the study intervention.

• 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.

• Previous history of participation in an H5 influenza A vaccine study. This includesany influenza subtypes that contain H5 such as H5N1, H5N8, or H5N6.

Note: The above information is not intended to contain all considerations relevant to a potential participation in a clinical trial.