This study will assess safety and immunogenicity of GSK Biologicals' H5N1 flu candidate vaccines GSK2590066A and GSK2340273A in healthy adults 18 - 49 years old.

Inclusion Criteria:

• Subjects who the investigator believes can and will comply with the requirements of the protocol.
• Written informed consent obtained from the subject.
• Male and female adults, 18-49 years of age at the time of the first vaccination.
• Satisfactory baseline medical assessment by history and physical examination.
• Safety laboratory test results within the parameters specified in the protocol.
• Access to a consistent means of telephone contact
• Female subjects of non-childbearing potential may be enrolled in the study. Female subjects of childbearing potential may be enrolled in the study, if the subject: has practiced adequate contraception for 30 days prior to vaccination, and has a negative urine pregnancy test on the day of first vaccination, and has agreed to continue adequate contraception during the entire treatment period and for 2 months after completion of the vaccination series.

Exclusion Criteria:

• Medical history of physician-confirmed infection with an H5N1 virus.
• Increased risk of occupational exposure to H5N1 influenza viruses.
• Previous vaccination at any time with an H5N1 vaccine, or with an oil-in water adjuvanted influenza vaccine.
• Planned administration of an adjuvanted influenza vaccine or an H5N1 pandemic vaccine during the entire study period.
• Use of any investigational or non-registered product other than the study vaccine(s) within 30 days preceding the first dose of study vaccine, or planned use during the study period.
• Presence of significant acute or chronic, uncontrolled medical or psychiatric illness.
• Presence of neurological or psychiatric diagnoses which, although stable, are deemed by the investigator to render the potential subject unable/unlikely to provide accurate safety reports.
• Evidence of current substance abuse, including alcohol, by medical history.
• Presence of a temperature >= 38.0ºC (≥100.4ºF), or acute symptoms greater than "mild" severity on the scheduled date of first dose.
• Diagnosed with cancer, or treatment for cancer, within 3 years. Persons with a history of cancer who are disease-free without treatment for 3 years or more are eligible.
• Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history and physical examination.
• Receipt of systemic glucocorticoids within 1 month prior to study enrollment, or any other cytotoxic or immunosuppressive drug within 6 months of study enrollment.
• 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 significant disorder of coagulation or treatment with warfarin derivatives or heparin. Persons receiving individual doses of low molecular weight heparin, outside of 24 hours prior to dosing, are eligible. Persons receiving prophylactic antiplatelet medications.
• An acute evolving neurological disorder or history of Guillain-Barré syndrome.
• Administration of an inactivated seasonal influenza vaccine within 14 days before the first study vaccine dose, or of any other vaccine(s) not foreseen by the study protocol within 30 days before the first study vaccine dose. The administration of live attenuated trivalent seasonal influenza virus vaccine (LAIV) is allowed.
• Planned administration of any vaccine(s) not foreseen by the study protocol through completion of the Day 42 visit. The administration of LAIV is allowed.
• Any known or suspected allergy to any constituent of influenza vaccines or to latex, or history of severe reaction to a previous influenza vaccination.
• Known pregnancy or a positive urine beta-human chorionic gonadotropin (β-hCG) test result prior to the first study vaccine dose.
• Lactating or nursing women.

Patient-level data for this study will be made available through www.clinicalstudydatarequest.com following the timelines and process described on this site.