Immunogenicity and Safety Study to Assess Influenza Vaccine Formulated With Haemagglutinin (HA) Antigen From Two Different Suppliers

Inclusion Criteria: * Healthy female and male adults * Aged ≥18 years on Day 1 * Written informed consent Exclusion Criteria: * Acute exacerbation of bronchopulmonary infection (cough, sputum, lung findings) or other acute disease * Acute febrile illness (≥38.0 °C) * Prior vaccination with an influenza vaccine (including the H1N1 pandemic swine flu vaccine) in the past 330 days * Known hypersensitivity to any vaccine component * Previous history of a serious adverse reaction to influenza vaccine * History of egg protein allergy or severe atopy * Known blood coagulation disorder * Chronic (longer than 14 days) administration of immunosuppressants or other immune-modifying drugs within 6 months before the first dose of the study vaccine, incl. oral corticosteroids in dosages of ≥0.5 mg/kg/d prednisolone or equivalent (inhaled or topical steroids are allowed) * Known immunodeficiency (incl. leukemia, cancer, HIV seropositivity) * Investigational medicinal product received in the past 3 months (90 days) * Treatment with immunoglobulins or blood transfusion(s) received in the past 3 months (90 days) * Pregnancy or lactation * Participation in another clinical trial * Employee at the investigational site, or spouse and children of the investigator, or relative living in the same household as the investigator and/or are dependent on the investigator * Suspected non-compliance