The primary objective of this trial is to demonstrate the equivalence, in terms of immunogenicity, of three different industrial lots of the investigational vaccine thereby supporting consistency of the manufacturing process.

Secondary Objectives:

Immunogenicity

To demonstrate that the investigational vaccine induces an immune response at least as good as the one induced by the reference vaccine, in terms of antibody titers.

To assess the immunogenicity of the investigational vaccine using parameters defined in the European Medicines Agency (EMEA) Note for Guidance (CPMP/BWP/214/96).

Safety:

To demonstrate that the investigational vaccine is at least as well tolerated as the reference vaccine, in terms of defined safety profile.

To describe the safety profile after vaccination.

Comfort of the vaccination assessment:

To assess the pain immediately after the injection using a Verbal Rating Scale. To describe the vaccination comfort after the injection using a -Patient-Reported Outcome questionnaire: the Vaccination Comfort Questionnaire.

Inclusion Criteria :

• Aged 18 to 60 years on the day of inclusion.
• Informed consent form signed.
• Able to attend all scheduled visits and to comply with all trial procedures.
• For a woman, inability to bear a child or negative urine pregnancy test at the first visit.

Exclusion Criteria :

• Systemic hypersensitivity to egg proteins, chick proteins, or any of the vaccine components, in particular, neomycin, formaldehyde, and octoxinol 9, or history of a life-threatening reaction to the trial vaccine or a vaccine containing the same substances.
• Febrile illness (oral temperature >= 37.5°C, or rectal equivalent temperature >= 38.0°C) on the day of inclusion.
• Participation in another clinical trial in the 4 weeks preceding the trial vaccination.
• Planned participation in another clinical trial during the present trial period.
• Congenital or acquired immunodeficiency, immunosuppressive therapy such as anti-cancer chemotherapy or radiation therapy within the preceding 6 months, or long-term systemic corticosteroids therapy.
• Unstable chronic illness (defined as illness requiring hospitalization or a clinically significant change in medication in the 12 weeks prior to inclusion) at a stage that could interfere with trial conduct or completion.
• Current abuse of alcohol or drug addiction that may interfere with the subject's ability to comply with trial procedures.
• Blood or blood-derived products received in the past 3 months.
• Any vaccination in the 4 weeks preceding the trial vaccination.
• Vaccination planned in the 4 weeks following the trial vaccination.
• Previous vaccination against influenza (in the previous 6 months).
• Thrombocytopenia or bleeding disorder contraindicating intramuscular vaccination.
• Subject deprived of freedom by an administrative or court order, or in an emergency setting, or hospitalized without his/her consent.