Effect of High-Dose Quadrivalent Influenza Vaccine (Efluelda®) Versus Standard-Dose (QIV-SD), in Subjects 65 Years of Age and Older on Innate Immunity, Including Gene Expression

Inclusion Criteria: 1. Aged 65 years or older, the day of inclusion; 2. Have signed and dated Informed Consent Form; 3. Able and willing to attend all scheduled visits, and to comply with study procedures; 4. Covered by French health insurance. Non-Inclusion Criteria : 1. Any vaccine injection (including COVID-19 vaccine) in the 4 weeks preceding study inclusion; 2. Plan to receive any vaccine (including COVID-19 vaccine) in the 4 weeks following study inclusion; 3. Already vaccinated against influenza for 2021-2022 season; 4. Hypersensitivity to any of the vaccine components, or history of a life-threatening reaction to the vaccines used in the study or to a vaccine containing any of the same substances; 5. HIV infection; 6. Active Hepatitis B, or active Hepatitis C; 7. Previous Guillain Barré syndrome; 8. Ongoing immunosuppressive treatment or active immunodeficiency; 9. Receipt of immune globulins, blood or blood-derived products in the past 3 months; 10. Thrombocytopenia or bleeding disorder, receipt of anticoagulants contraindicating IM vaccination based on investigator's judgment; 11. Influenza-like illness symptoms, including COVID-19, within 4 weeks before study inclusion; 12. Personnes referred to in articles L1121-6 and L1121-8 of Public Health Code (persons deprived of liberty by judicial or administrative decision and persons subject to a legal protection measure: guardianship or curatorship). Exclusion Criteria: 1. Any subject presenting with influenza-like illness symptoms, including COVID-19 between inclusion (visit 1) and randomization (visit 2); 2. Subject unable to attempt visit at Day 0 (visit 2) and Day 1 (visit 3); 3. Blood sample at Day 0 (visit 2) impossible to obtain; 4. Receipt of vaccine injection or equivalent between inclusion (visit 1) and randomization (visit 2), other than those allowed and planned in the study. This includes non-study dose of 2021-2022 influenza vaccine, blood-derived immune globulins, blood, or blood-derived products. 5. Any unexpected event relevant to the physician in charge, after discussion with the coordinating investigator and the sponsor