Immunogenicity and Safety Study of GlaxoSmithKline (GSK) Biologicals' Herpes Zoster Subunit (HZ/su) Vaccine (GSK1437173A) in Adults ≥ 65 Years of Age With and Without Zostavax® Vaccination at Least 5 Years Earlier

Inclusion Criteria: * Subjects who, in the opinion of the investigator, can and will comply with the requirements of the protocol. * A male or female ≥ 65 years of age at the time of the first vaccination. * Written informed consent obtained from the subject prior to performing any study specific procedure. For the No prev-Zvax group only: • No previous vaccination with Zostavax. For the Prev-Zvax group only: • Previous vaccination with Zostavax ≥ 5 calendar years earlier. * Documentation indicating the date of previous Zostavax vaccination will be required. Exclusion Criteria: * Previous vaccination with Zostavax \< 5 calendar years earlier and/or anyone that ever received more than a single dose of Zostavax. * Previous vaccination against VZV, administration of HZ/su vaccine or any other investigational or non-registered HZ vaccine (except Zostavax for the Prev-Zvax group). * Use of any investigational or non-registered product other than the study vaccine during the period starting 30 days before the first dose of study vaccine, or planned use during the study period. * Chronic administration (defined as \> 14 consecutive days) of immunosuppressants or other immune-modifying drugs in the period starting 6 months prior to the first dose of vaccine. (For corticosteroids, a prednisone dose of \< 20 mg/day, or equivalent, is allowed.) Inhaled, topical and intra-articular corticosteroids are allowed. * Administration of long-acting immune-modifying drugs (e.g., infliximab) in the period starting 6 months prior to the first vaccine dose or expected administration at any time during the study period. * Administration or planned administration of a live vaccine in the period starting 30 days before the first dose of study vaccine and ending 30 days after the last dose of study vaccine, or, administration or planned administration of a non-replicating vaccine in the period starting 8 days prior to and ending 14 days after either dose of study vaccine. * Current participation in or planned concurrent participation in another clinical study, at any time during the study period, in which the subject has been or will be exposed to an investigational or a non-investigational product. * Planned administration of an HZ vaccine (including an investigational or non-registered vaccine) other than the study vaccine during the entire study. * History of HZ or any suspected HZ between the screening visit and Visit 1. * History of any reaction or hypersensitivity likely to be exacerbated by any component of the vaccine/product. * 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) by oral route, axillary or tympanic setting, or ≥ 38.0°C/100.4°F on rectal setting. The recommended route for recording temperature in this study will be oral. * Subjects with a minor illness (such as mild diarrhea, mild upper respiratory infection) without fever may be enrolled at the discretion of the investigator. * Administration of immunoglobulins and/or any blood products in the period starting 3 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. * Any condition which, in the judgment of the investigator, would make intramuscular (IM) injection unsafe.