The Aim of This Study is to Investigate the Persistence of Antibody Response in Adults up to 15 Years After One Booster Dose of GlaxoSmithKline (GSK) Biologicals' Encepur Adults Vaccine

Inclusion Criteria: Inclusion criteria for all subjects: * Subjects who, in the opinion of the investigator, can and will comply with the requirements of the protocol. * Written informed consent obtained from the subject prior to performance of any study specific procedure. * Subjects who have participated in study V48P7E2 (NCT01562444) and who received in the parent V48P7 study one of the following schedules: rapid, conventional, or accelerated conventional and a booster vaccination in study V48P7E1 (NCT00387634) or before study V48P7E1 (NCT00387634) (only rapid schedule). Additional inclusion criteria for subjects who will need a second booster dose: * Healthy subjects as established by medical history and clinical examination before entering into the study. * Female subjects of non-childbearing potential may be enrolled in the study. Non-childbearing potential is defined as pre-menarche, current bilateral tubal ligation or occlusion, hysterectomy, bilateral ovariectomy or post-menopause. * Female subjects of childbearing potential can receive the booster vaccine 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 for 2 months after booster administration. Exclusion Criteria: Each subject must not be: * Unwilling or unable to give written informed consent to participate in the study. * Perceived to be unreliable or unavailable to complete the study. Each subject must not have: * Clinical conditions representing a contraindication to blood draws. * Any other clinical condition that, in the opinion of the investigator, might interfere with the results of the study or pose additional risk to the subject due to participation in the study. * Received an investigational or non-registered medicinal product within 30 days prior to informed consent. * Concurrently participating 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 vaccine/product. * Levels of NT\<10 in V48P7E2 (NCT01562444) study. * Previous vaccination against TBE or other Flavivirus diseases with other TBE and Flavivirus vaccines (e.g. Yellow fever vaccine, Dengue fever vaccine, Japanese encephalitis vaccine) before, during and after completion of the V48P7E2 (NCT01562444) and before starting TBEV POLYGELINE FREE-025 EXT 21 study. * Primary immunization with TBE vaccine in the parent study V48P7 according to the modified conventional (MC) schedule. * History of confirmed TBE infection. * Known exposure to other Flaviviruses. Each subject who will receive the second booster vaccination in this study additionally to the exclusion criteria above must not have: * Hypersensitivity, including allergy, to any component of vaccines, medicinal products or medical equipment whose use is foreseen in this study. * Clinical conditions representing a contraindication to intramuscular vaccination. * Progressive, unstable or uncontrolled clinical conditions. * Abnormal function of the immune system resulting from: Clinical conditions. Systemic administration of corticosteroids for more than 14 consecutive days within 90 days prior to informed consent. This will mean prednisone ≥20 mg/day (for adult subjects) or equivalent. Inhaled and topical steroids are allowed. Administration of antineoplastic and immuno-modulating agents or radiotherapy within 90 days prior to vaccination. * Received immunoglobulins or any blood products within 180 days prior to vaccination. * Administration of long-acting immune-modifying drugs at any time during the study period. * Acute disease and/or fever at the day of booster vaccination. * Expected general decrease in immune response. * Organic brain disturbances, including seizure disorders. * Progressive neurological disorders. * Suffered febrile or afebrile convulsions. * Serious chronic illness. * History of any reaction or hypersensitivity likely to be exacerbated by any component of the vaccine or chemically related substances. * Individuals who received any other vaccines within 14 days (for inactivated vaccines) or 28 days (for live vaccines) prior to vaccination in this study or who are planning to receive any vaccine within 28 days from the study vaccines. * Pregnant.