Safety and Immunogenicity of Different Dosing Schedules of GlaxoSmithkline (GSK) Biologicals' Herpes Zoster (HZ) Vaccine in Adults 50 Years of Age or Older

Inclusion Criteria: * Subjects who, in the opinion of the investigator, can and will comply with the requirements of the protocol. * A male or female aged 50 years or older at the time of the first vaccination. * Written informed consent obtained from the subject. * Female subjects of non-childbearing potential may be enrolled in the study. * Non-childbearing potential is defined as pre-menarche, current tubal ligation, hysterectomy, ovariectomy or post-menopause. * 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 pregnancy test on the day of vaccination, and * has agreed to continue adequate contraception during the entire treatment period and for two months after completion of the vaccination series. Exclusion Criteria: * Use of any investigational or non-registered product other than the study vaccine within 30 days preceding the first dose of study vaccine, or planned use during the study period. * Chronic administration of immunosuppressants or other immune-modifying drugs within six months prior to the first vaccine dose. For corticosteroids, a prednisone dose of \< 20 mg/day, or equivalent, is allowed. Inhaled, topical and intra-articular corticosteroids are allowed. * Administration or planned administration of a live vaccine in the period starting 30 days before and ending 30 days after either dose of study vaccine. * Administration or planned administration of a non-replicating vaccine within eight days prior to or within 14 days after either dose of study vaccine. * Administration of long-acting immune-modifying drugs (e.g. infliximab) within six months prior to the first vaccine dose or expected administration at any time during the study period. * Previous vaccination against varicella or HZ (either registered product or participation in a previous vaccine study). * Planned administration during the study of an HZ or varicella vaccine (including an investigational or non-registered vaccine) other than the study vaccine. * History of HZ. * History of any reaction or hypersensitivity likely to be exacerbated by any component of the vaccine(s). * Any confirmed or suspected immunosuppressive or immunodeficient condition resulting from disease (e.g. malignancy, human immunodeficiency virus \[HIV\] infection) or immunosuppressive/cytotoxic therapy (e.g. medications used during cancer chemotherapy, organ transplantation or to treat autoimmune disorders). * Acute disease and/or fever at the time of enrolment. * Fever is defined as temperature ≥ 37.5°C (99.5°F) for oral, axillary or tympanic route, or ≥ 38.0°C (100.4°F) for rectal route. The preferred route for recording temperature in this study will be oral. * Subjects with a minor illness (such as mild diarrhoea, mild upper respiratory infection) without fever may be enrolled at the discretion of the investigator. * Administration of immunoglobulins and/or any blood products within the three months preceding the first dose of study vaccine or planned administration during the study period. * Significant underlying illness that, in the opinion of the investigator, would be expected to prevent completion of the study. * Any other condition that, in the opinion of the investigator, might interfere with the evaluations required by the study. * Pregnant or lactating female. * Female planning to become pregnant during the entire treatment period and for two months after completion of the vaccination series, or planning to discontinue contraceptive precautions (if of childbearing potential).