Consistency Study of GlaxoSmithKline (GSK) Biologicals' MMR Vaccine (209762) (Priorix) Comparing Immunogenicity and Safety to Merck & Co., Inc.'s MMR Vaccine (M-M-R II), in Children 12 to 15 Months of Age

The purpose of this study is to evaluate consistency in terms of the immune response to three different lots of GSK Biologicals' trivalent MMR vaccine manufactured to target potencies, and compare its immunogenicity to Merck \& Co., Inc.'s MMR vaccine, which is approved for use in the United States (US).

This study will evaluate the consistency of the immune response to three different lots of GSK Biologicals' trivalent investigational MMR vaccine (referred to as INV_MMR vaccine, throughout this document) and compare its immunogenicity 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 INV_MMR vaccine will be given as one of three consistency lots manufactured to target potencies designated as INV_MMR_L1, INV_MMR_L2 and INV_MMR_L3. The COM_MMR vaccine will be given as one of two lots designated COM_MMR_L1 and COM_MMR_L2 and will be analysed as pooled lots within the study. The MMR vaccine will be co-administered with Varivax (VV), Havrix (HAV) and (in the US sub-cohort only) Prevnar 13 (PCV-13) which are routinely administered to children of this age in the US.

Eligibility Criteria:
Inclusion Criteria:

* Male or female child between 12 and 15 months of age at the time of vaccination.
* The investigator believes that the parent(s) or Legally Acceptable Representative(s) (LAR(s)) of the child, can, and will comply with the requirements of the protocol.
* Written informed consent obtained from the parent(s)/LAR(s) of the child.
* Child is in stable health as determined by investigator's clinical examination and assessment of child's medical history.

For US children only:

• Child that previously received a 3-dose series of Prevnar 13 only (i.e., no doses given as Prevnar/Prevenar), with the last dose at least 60 days prior to study entry.

Exclusion Criteria:

* Child in care.
* Use of any investigational or non-registered product other than the study vaccine(s) during the period starting 30 days before the day of study vaccination (i.e., 30 days prior to Day 0) or planned use during the entire study period.
* Concurrently participating in another clinical study, in which the child has been or will be exposed to an investigational or a non-investigational product.
* Chronic administration of immunosuppressants, or other immune-modifying drugs during the period starting 180 days prior to the first vaccine dose or any planned administration of immunosuppressive and immune-modifying drugs during the entire study.

  * For corticosteroids, this will mean prednisone, ≥0.5 mg/kg/day or equivalent.
  * Inhaled and topical steroids are allowed.
* Planned administration/ administration of a vaccine not foreseen by the study protocol during the period starting 30 days prior to study vaccination at Visit 1 and ending at Visit 2. Please Note:

  * Inactivated influenza (Flu) vaccine and Haemophilus influenzae type b conjugate vaccine (Hib) vaccines may be given at any time, including the day of study vaccination (Flu and Hib vaccines must be administered at a different location than the study vaccine/s).
  * Any other age appropriate vaccine may be given starting at Visit 2 and anytime thereafter.
* Administration of immunoglobulins and/or any blood products during the period starting 180 days prior to study vaccination at Visit 1 or planned administration from the date of vaccination through the immunogenicity evaluation at Visit 2.
* History of measles, mumps, rubella, varicella/zoster and/or hepatitis A disease.
* Known exposure to measles, mumps, rubella and/or varicella/zoster during the period starting within 30 days prior to first study vaccination.
* Previous vaccination against measles, mumps, rubella, hepatitis A and/or varicella virus.
* Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history and physical examination.
* A family history of congenital or hereditary immunodeficiency.
* History of allergic disease or reactions likely to be exacerbated by any component of the vaccines, including hypersensitivity to neomycin, latex or gelatin.
* Blood dyscrasias, leukemia, lymphomas of any type, or other malignant neoplasms affecting the bone marrow or lymphatic systems.
* Acute disease at the time of enrollment. All vaccines can be administered to persons with a minor illness such as diarrhea, mild upper respiratory infection without fever.
* Active untreated tuberculosis based on medical history.
* Any other condition which, in the opinion of the investigator, prevents the child from participating in the study.

For US children only:

* Child that previously received a vaccination with heptavalent Prevnar/Prevenar (prior vaccination should be with 3 doses of Prevnar 13 only).
* Child that previously received a fourth dose of any pneumococcal conjugate vaccine.