Comparison of GSK Measles-mumps-rubella-varicella (MMRV) Vaccine Versus PriorixTM

Inclusion Criteria: * 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. * Male or female subjects between and including 9 and 10 months of age at the time of the first vaccination. * Written informed consent obtained from the the parent or guardian of the subject. * Healthy subjects as established by medical history and clinical examination before entering into the study. Exclusion Criteria: * Use of any investigational or non-registered product other than the study vaccines 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. * Planned administration/administration of a vaccine not foreseen by the study protocol starting 30 days prior to administration of any dose of the study vaccine, up to 42 days after the vaccine dose with the exception of hepatitis A vaccine and oral poliovirus vaccine . * 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-registered product. * Previous vaccination against measles, mumps, rubella and varicella. * History of measles, mumps, rubella and/or varicella diseases. * Known exposure to measles, mumps, rubella and/or varicella within 30 days prior…