A Study of High-Dose Trivalent Inactivated Influenza Vaccine in Adults 50 to 64 Years of Age

Inclusion Criteria: * Aged 50 to 64 years (inclusive) on the day of vaccination * Informed consent form has been signed and dated * Medically stable * 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 vaccination until at least 4 weeks after vaccination Exclusion Criteria: * Known pregnancy, or a positive urine pregnancy test * Currently breastfeeding a child * Participation in another clinical trial investigating a vaccine, drug, medical device, or medical procedure in the 4 weeks preceding the trial vaccination * Planned participation in another clinical trial during the present trial period * Planned receipt of any vaccine in the 4 weeks following the trial vaccination (prior to the Visit 2 blood draw) * Receipt of seasonal or pandemic influenza vaccine in the past 6 months * Receipt of blood or blood-derived products in the past 3 months * Systemic hypersensitivity to eggs, chicken proteins, or any of the vaccine components, or a history of a life-threatening reaction to the standard-dose Trivalent Inactivated Influenza Vaccine or a vaccine containing any of the same substances * 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 * Neoplastic disease or any hematologic malignancy * Bleeding disorder, or receipt of anticoagulants in the 3 weeks preceding inclusion, contraindicating intramuscular vaccination * Personal history of Guillain-Barré Syndrome * Self-reported 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 abuse or drug addiction that 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