A Study to Explore the Existence of Horizontal Transmission of the RIX4414 Vaccine Strain Between Twins Within a Family.

Inclusion Criteria: * Subjects with a live twin living in the same household who is also enrolled in this study. * Born after a gestation period of ≥32 weeks, * Discharged from hospital neonatal care stay, * Subjects who the investigator believes that their parents/guardians can and will comply with the requirements of the protocol should be enrolled in the study. * A male or female between, and including, 6 and 14 weeks of age at the time of the first study vaccination. * Healthy subjects as established by medical history and clinical examination before entering into the study. * Written informed consent obtained from the parent or guardian of the subjects. Exclusion Criteria: * Use of any investigational or non-registered product (drug or vaccine) other than the study vaccine(s) within 30 days preceding the first dose of study vaccine, or planned use during the study period. * Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history and physical examination (no laboratory testing required). * Any clinically significant history of chronic gastrointestinal disease. * History of allergic disease or reactions likely to be exacerbated by any component of the vaccine. * Acute disease at time of enrolment. * Administration of immunoglobulins and/or any blood products since birth or planned administration during the study period. * Contact with an immunosuppressed individual. * 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 (pharmaceutical product or device). * Chronic administration of immunosuppressants since birth. * Gastroenteritis within 7 days preceding the first study vaccine administration. * Documented HIV-positive subject.