The aim of the study is to evaluate a prototype quadrivalent influenza vaccine (QIV), the licensed 2010-2011 trivalent influenza vaccine (TIV) containing the primary B strain, and the investigational TIV containing the alternate B strain in adult subjects.

Primary Objective:

• To demonstrate non-inferiority of antibody responses to QIV compared with licensed 2010-2011 TIV (containing the primary B strain) and investigational TIV (containing the alternate B strain) as assessed by geometric mean titer (GMT) ratios for each of the four virus strains separately among subjects 65 years of age and older

Observational Objective:

• To describe the safety profiles of TIV among subjects 18 years of age and older and QIV in subjects 65 years and older, as assessed by solicited injection site and systemic adverse events (AEs) collected for 7 days post-vaccination, unsolicited adverse events collected from 21 days post-vaccination, and adverse events of special interest and serious adverse events (SAEs) collected from Visit 1 to Visit 2.

All participants will receive a single dose of their assigned vaccine during Visit 1. They will be followed up for safety and immunogenicity through Day 21 post-vaccination (Visit 2)

Inclusion criteria:

• Subject is 18 years of age or older on the day of inclusion.
• Informed consent form (ICF) has been signed and dated.
• Able to attend all scheduled visits and to comply with all trial procedures.
• For a woman of childbearing potential, use of an effective method of contraception or abstinence from at least 4 weeks prior to the first vaccination until at least 4 weeks post-vaccination.

Exclusion criteria:

• Known pregnancy, or a positive urine pregnancy test.
• Currently breastfeeding a child.
• History of serious adverse reaction to any influenza vaccine.
• Receipt of any vaccine in the 4 weeks preceding the trial vaccination.
• Planned receipt of any vaccine between Visit 1 and Visit 2.
• Participation in another interventional clinical trial investigating a vaccine, drug, medical device, or medical procedure in the 4 weeks preceding the first study vaccination or during the course of the study.
• Receipt of any influenza vaccine since 01 August 2010 (including 2009 H1N1 monovalent vaccine).
• Known systemic hypersensitivity to any of the vaccine components, or history of a life-threatening reaction to the vaccine(s) used in the trial or to a vaccine containing any of the same substances.
• Receipt of blood or blood-derived products in the past 3 months, which might interfere with assessment of the immune response.
• Thrombocytopenia, bleeding disorder, or receipt of anticoagulants contraindicating intramuscular vaccination.
• Any condition that in the opinion of the Investigator would pose a health risk to the subject if enrolled or could interfere with the evaluation of the vaccine.
• Personal history of Guillain-Barré Syndrome (GBS).
• 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).
• Any chronic illness that, in the opinion of the Investigator, is not well controlled or that may interfere with trial conduct or completion or with assessment of adverse events.
• Known seropositivity for human immunodeficiency virus (HIV), hepatitis B, or hepatitis C.
• Deprived of freedom by an administrative or court order, or in an emergency setting, or hospitalized involuntarily.
• Current alcohol or drug use that, in the opinion of the Investigator, might interfere with the ability to comply with trial procedures.
• Identified as employees of the Investigator or study center, with direct involvement in the proposed study or other studies under the direction of that Investigator or study center, as well as family members (i.e., immediate, husband, wife and their children, adopted or natural) of the employees or the Investigator.