Safety and Immunogenicity of High-Dose Quadrivalent Influenza Vaccine in Patients ≥65 Years

Inclusion Criteria: * Aged \>= 65 years on the day of inclusion. * Informed consent form has been signed and dated. * Able to attend all scheduled visits and to comply with all study procedures. Exclusion Criteria: * Participation at the time of study enrollment (or in the 4 weeks preceding the study vaccination) or planned participation during the present study period in another clinical study investigating a vaccine, drug, medical device, or medical procedure. * Receipt of any vaccination with live vaccines within the past 27 days preceding the study vaccination or any vaccination with inactivated vaccines within the past 6 days preceding the study vaccination, or planned receipt of any vaccine prior to Visit 3. * Previous vaccination against influenza (in the preceding 6 months) with either the study vaccine or another vaccine. * Receipt of immune globulins, blood or blood-derived products in the past 3 months. * 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). * Known systemic hypersensitivity to eggs, chicken proteins, or any of the vaccine components, or history of a life-threatening reaction to the vaccine used in the study or to a vaccine containing any of the same substances. * Thrombocytopenia or bleeding disorder, contraindicating IM vaccination based on Investigator's judgment. * Deprived of freedom by an administrative or court order, or in an emergency setting, or hospitalized involuntarily. * Alcohol or substance abuse that, in the opinion of the Investigator might interfere with the study conduct or completion. * Chronic illness that, in the opinion of the Investigator, was at a stage where it might interfere with study conduct or completion. * Identified as an Investigator or employee of the Investigator or study center with direct involvement in the proposed study, or identified as an immediate family member (i.e., parent, spouse, natural or adopted child) of the Investigator or employee with direct involvement in the proposed study. * Personal or family history of Guillain-Barré syndrome. * Neoplastic disease or any hematologic malignancy (except localized skin or prostate cancer that was stable at the time of vaccination in the absence of therapy and participants who had a history of neoplastic disease and have been disease free for \>=5 years). * Moderate or severe acute illness/infection (according to Investigator judgment) on the day of vaccination or febrile illness (temperature \>=37.5°Celsius). A prospective participant were not be included in the study until the condition had resolved or the febrile event had subsided. * History of convulsions.