Immunogenicity and Safety Study of GlaxoSmithKline (GSK) Biologicals' Combined Measles-mumps-rubella (MMR) Vaccine in Children in Their Second Year of Life

This trial is a Phase IIIA, randomized, observer-blind, controlled, multi-center, multi-country study with four parallel groups. This study will evaluate the immunogenicity and safety of GSK Biologicals' trivalent investigational MMR vaccine (referred to as Inv\_MMR vaccine, throughout this document) in contrast to the US standard of care comparator vaccine (M-M-R II, Merck and Co., Inc., referred to as Com\_MMR throughout this document) in children during their second year of life. The first dose of this two-dose study is designed to establish the end of shelf-life potency of Inv\_MMR vaccine. The Inv\_MMR vaccine will be given as one of two lots; one of a minimum potency, designated Inv\_MMR\_Min; and the other at a mid-range or medium potency designated Inv\_MMR\_Med to two groups. The second dose for both of these Inv\_MMR groups will have a potency within the release range of the marketed vaccine. The Com\_MMR vaccine will consist of two lots designated Com\_MMR\_L1 and Com\_MMR\_L2 and will be analyzed as pooled lots within the study. The first MMR vaccine dose will be co-administered with Varivax, Havrix and (in the US sub-cohort only) Prevnar 13 which are routinely administered to children of this age in the US.