Immunogenicity & Safety of GSK's Influenza Vaccine 1557484A Given to Adults Aged ≥18 Years

Inclusion Criteria: * A male or female 18 years of age or greater at the time of the first vaccination. * Written informed consent obtained from the subject. * Among 18 to 49 year old subjects, good general health as established by medical history and clinical examination before entering into the study. * Among subjects \> 49 years of age, stable health status within 1 month prior to enrollment. * Access to a consistent means of telephone contact. * Comprehension of the study requirements, ability to comprehend and comply with procedures for collection of short- and long-term safety data, expressed availability for the required study period, and ability and willingness to attend scheduled visits. Exclusion Criteria: * Evidence of substance abuse or of neurological or psychiatric diagnoses which, even if clinically stable, are deemed by the investigator to render the potential subjectunable/unlikely to provide accurate safety reports. * Diagnosed with cancer, or treatment for cancer, within 3 years. * An oral temperature ≥37.8º C, or acute symptoms greater than "mild" severity on the scheduled date of first vaccination. * Any confirmed or suspected immunosuppressive or immunodeficient condition including history of human immunodeficiency virus infection. * Receipt of systemic glucocorticoids within 1 month of study enrollment, or any other cytotoxic or immunosuppressive drug within 6 months of study enrollment. * Any significant disorder of coagulation or treatment with Coumadin derivatives or heparin. * Administration of any vaccines within 30 days before study enrollment. * Previous administration of any H5N1 vaccine. * Use of any investigational or non-registered product or planned participation in another investigational study within 30 days prior to study enrollment, or during the 364 days following the first test article dose. Use of any investigational or non-registered product with immunosuppressive properties is exclusionary at any time during the trial. * Receipt of any immunoglobulins and/or any blood products within 3 months of study enrollment or planned administration of any of these products during the study period. * Any known or suspected allergy to any constituent of influenza vaccines; a history of anaphylactic-type reaction to consumption of eggs; or a history of severe adverse reaction to a previous influenza vaccine. * Known pregnancy or a positive urine beta-human chorionic gonadotropin test result prior to either vaccination. * Lactating or nursing. * Women of child bearing potential who lack a history of reliable contraceptive practices. The provision of this history does NOT replace the requirement to perform, and obtain negative results in pregnancy urine tests prior to treatments. * Known use of an analgesic or antipyretic medication within 12 hours prior to first treatment.