Immunogenicity and Safety of Booster Dose of PoliorixTM Vaccine in Previously Vaccinated Toddlers

Inclusion Criteria: * Subjects who the investigator believes that their parent(s)/Legally Acceptable Representative(s) can and will comply with the requirements of the protocol. * Subjects who received the complete three-dose primary vaccination course in study NCT01021293. * Healthy male or female toddlers 18 to 24 months of age at the time of Visit 1 (Day 0). * Written informed consent obtained from the parent(s)/ Legally Acceptable Representative(s) of the subject. * Healthy subjects as established by medical history and clinical examination before entering into the study. Exclusion Criteria: * Child in care. * Use of any investigational or non-registered product other than the study vaccine(s) within 30 days preceding the booster dose of study vaccine(s), or planned use during the study period. * Chronic administration of immunosuppressants or other immune-modifying drugs within six months prior to Visit 1 (Day 0). * Administration of immunoglobulins and/or any blood products within the 3 months preceding Visit 1 (Day 0) or planned administration during the study period. * Administration of a vaccine not foreseen by the study protocol within 30 days of Visit 1 (Day 0) or planned administration during the study period. * 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 product. * Evidence of previous booster vaccination against poliomyelitis or the disease since the conclusion visit of Study NCT01021293. * History of seizures or progressive neurological disease. * Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history and physical examination. * History of any reaction or hypersensitivity likely to be exacerbated by any component of the vaccine. * Major congenital defects or serious chronic illness. * Acute disease and/or fever at the time of enrolment.