Immunogenicity and Safety Study of GlaxoSmithKline (GSK) Biologicals' Influenza Vaccine(s) GSK3206641A and GSK3206640A Administered in Adults 18 to 64 Years of Age

Inclusion Criteria: * Male or female adults who are 18 to 64 years of age (inclusive) at the time of first study vaccination. * Written informed consent obtained from subject. * Subjects who the investigator believes can and will comply with the requirements of the protocol . * Healthy subjects as established by medical history and physical examination. * Access to a consistent means of telephone contact. * For subjects who undergo a screening visit: results of all safety laboratory tests obtained at the screening visit must be within reference ranges. Results of any repeat testing cannot be used to qualify a subject for enrolment. * Female subjects of non-childbearing potential may be enrolled in the study. Non-childbearing potential is defined as current tubal ligation, hysterectomy, ovariectomy or post-menopause. * Female subjects of childbearing potential may be enrolled in the study, if they * have practiced adequate contraception for 30 days prior to vaccination, and * have a negative pregnancy test on the day of vaccination, and * agree to continue to practice adequate contraception until 2 months after the last dose administered. Exclusion Criteria: * Presence or evidence 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. * Presence or evidence of substance abuse. * Diagnosed with cancer, or treatment for cancer within three years. * Diagnosed with excessive daytime sleepiness, or narcolepsy; or history of narcolepsy in a subject's parent, sibling or child. * Presence of a temperature ≥ 38.0ºC (≥100.4ºF), 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 (HIV) infection. * Receipt of systemic glucocorticoids within 30 days prior to the first dose of study vaccine/placebo, or any other cytotoxic, immunosuppressive or immune-modifying drugs within 6 months of first study vaccine/ placebo dose. * Any significant disorder of coagulation or treatment with warfarin derivatives or heparin. * An acute evolving neurological disorder or Guillain Barré Syndrome within 42 days of receipt of prior seasonal or pandemic influenza vaccine. * Administration of an inactive vaccine within 14 days or of a live attenuated vaccine within 30 days before the first dose of study vaccine/placebo. * Planned administration of any vaccine other than the study vaccine/placebo before blood sampling at the Day 42 visit. * Previous administration of any H7 vaccine or physician-confirmed H7 disease. * Use of any investigational or non-registered product other than the study vaccine within 30 days preceding the first dose of study vaccine/placebo, or planned use during the study period. * Receipt of any immunoglobulins and/or any blood products within 90 days before the first dose of study vaccine/placebo, or planned administration of any of these products during the study period. * Any known or suspected allergy to any constituent of influenza vaccines or component used in the manufacturing process of the study vaccine including 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 (β-hCG) test result before the first dose of study vaccine/placebo. * Lactating or nursing women. * Any condition which, in the opinion of the investigator, prevents the subject from participating in the study.