Study of Influenza Vaccines Containing an Additional H3 Antigen in Healthy Adult Participants 18 to 49 Years of Age and 60 Years of Age and Older

Inclusion criteria

• Aged 18 to 49 years (Stage 1) or 60 years of age and older (Stage 2) on the day of inclusion
• Participants who are healthy as determined by medical evaluation including medical history and physical examination, if deemed necessary
• A female participant is eligible to participate if she is not pregnant or breastfeeding and one of the following conditions applies:

• Is of non-childbearing potential. To be considered of non-childbearing potential, a female must be post-menopausal for at least 1 year, or surgically sterile OR
• Is of childbearing potential and agrees to use an effective contraceptive method from at least 4 weeks prior to study intervention administration until at least 3 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) before the first dose of study intervention.

Exclusion criteria

Participants are excluded from the study if any of the following criteria apply:

• Known or suspected congenital or acquired immunodeficiency; or receipt of immunosuppressive 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 3 months)
• History of clinically- or laboratory-confirmed diagnosis of influenza infection in the last 12 months
• Known systemic hypersensitivity to any of the study intervention components, or history of a life-threatening reaction to the study interventions used in the study or to a product containing any of the same substances
• Bleeding disorder, or receipt of anticoagulants in the 3 weeks preceding inclusion, contraindicating intramuscular injection, based on investigator's judgment
• Chronic illness that, in the opinion of the investigator, is at a stage where it might interfere with study conduct or completion
• Moderate or severe acute illness/infection (according to investigator judgment) or febrile illness (temperature ≥ 38.0°C) on the day of study intervention administration. A prospective participant should not be included in the study until the condition has resolved or the febrile event has subsided
• Self-reported or prior documented seropositivity for human immunodeficiency virus, hepatitis B, or hepatitis C
• Body mass index of 40 or higher
• Current or past diagnosis, personal or in the family, of Guillain-Barré syndrome
• Have known or recently active (within 12 months) neoplastic disease or a current or past diagnosis of any hematologic malignancy
• Receipt of any vaccine in the 4 weeks preceding the study intervention administration or planned receipt of any vaccine in the 3 weeks (approximately 21 days, or until the end of study participation) following study intervention administration
• Previous vaccination against influenza (in the year 2024) with an investigational or marketed vaccine. In the case of adults ≥ 60 years of age (Stage 2 of the study), previous vaccination within 6 months' time period will apply.
• Receipt of immune globulins, blood or blood-derived products in the past 3 months
• Any change in chronic prescription medication or change in medication dose or dosage in the 60 days prior to enrollment

The above information is not intended to contain all considerations relevant to a participant's potential participation in a clinical trial.