Safety and Immunogenicity of Different Formulations of an MF59-Adjuvanted Influenza Vaccine in Older Adults

INCLUSION CRITERIA: In order to participate in this study, all subjects must meet ALL of the inclusion criteria described. 1. Individuals ≥50 years of age on the day of informed consent. 2. Individuals who have voluntarily given written consent after the nature of the study has been explained according to local regulatory requirements, prior to study entry. 3. Individuals who can comply with study procedures including follow-up . 4. Males, females of non-childbearing potential or females of childbearing potential who are using an effective birth control method, at least 30 days prior to informed consent, which they intend to use for at least 2 months after the study vaccination. EXCLUSION CRITERIA: In order to participate in this study, all subjects must not meet ANY of the exclusion criteria described below: 1. Females of childbearing potential who are pregnant, lactating, or who have not adhered to a specified set of contraceptive methods from at least 30 days prior to informed consent and who do not plan to do so for at least 2 months after the study vaccination. 2. Progressive, unstable or uncontrolled clinical conditions. 3. Hypersensitivity, including allergy, to any component of vaccines whose use is foreseen in this study. 4. History of any medical condition considered an adverse event of special interest (AESI). 5. Known history of Guillain-Barré syndrome or another demyelinating disease such as encephalomyelitis and transverse myelitis. 6. Clinical conditions representing a contraindication to intramuscular administration of vaccines or blood draw. 7. Abnormal function of the immune system resulting from: 1. Clinical conditions. 2. Systemic administration of corticosteroids (PO/IV/IM) at a dose of ≥20 mg/day of prednisone or equivalent for more than 14 consecutive days within 90 days prior to informed consent. 3. Administration of antineoplastic and immunomodulating agents or radiotherapy within 90 days prior to informed consent. 8. Receipt of immunoglobulins or any blood products within 180 days prior to informed consent. 9. Receipt of an investigational or non-registered medicinal product within 30 days prior to vaccination. 10. Individuals who received any other vaccines within 14 days (for inactivated vaccines) or 28 days (for live vaccines) prior to enrolment in this study or who are planning to receive any vaccine within 28 days from the study vaccines. 11. Study personnel or immediate family or household member of study personnel. 12. Receipt of any influenza vaccine within 6 months prior to vaccination in this study, or plan to receive an influenza vaccine during the study period. 13. Acute (severe) febrile illness. 14. Any other clinical condition that, in the opinion of the investigator, might interfere with the results of the study or pose additional risk to the subject due to participation in the study.