Safety and Immunogenicity Study of GlaxoSmithKline (GSK) Biologicals' Measles, Mumps and Rubella (MMR) Vaccine (209762) Compared to Merck & Co., Inc.'s MMR Vaccine in Healthy Children 12 to 15 Months of Age

The purpose of this study is to evaluate the immunogenicity and safety of GSK Biologicals' trivalent MMR (Priorix), comparing it to Merck's MMR vaccine (M-M-R II), which is approved for use in the US in healthy children 12 to 15 months of age.

This study will evaluate the safety of GSK's trivalent MMR vaccine (referred to as INV_MMR vaccine) at a potency that will be used to define maximum release limits for the INV_MMR in comparison to the US standard of care (M-M-R II/ M-M-R VaxPro vaccine referred to as COM_MMR vaccine). In order to obtain more representative data on the comparator vaccine, the COM_MMR used in this study will consist of two lots designated COM_MMR_L1 and COM_MMR_L2. Throughout the study COM_MMR_L1 and COM_MMR_L2 will be analyzed as pooled lots. This study is intended to support licensure of GSK's MMR vaccine in the US.

All children will receive Varivax and Havrix vaccines, concomitantly with MMR containing vaccine at 12 to 15 months of age. Prevnar 13 will be administered only to US children. At the end of the study, GSK will provide a second dose of Havrix and/or varicella vaccine to participants enrolled in selected non-US countries if local health departments do not routinely provide hepatitis A and varicella vaccination. The second dose of Havrix and varicella vaccine is not part of the study procedures.

Eligibility Criteria:
Inclusion Criteria:

* Male or female child between 12 and 15 months of age (e.g., from the 1 year birthday until the day before age 16 months) at the time of vaccination.
* Subjects' parent(s)/Legally Acceptable Representative(s) \[LAR(s)\] who, in the opinion of the investigator, 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: a child who received all routine vaccinations as per ACIP recommendations prior to study entry: completion of hepatitis B and rotavirus series and completion of the primary series of diphtheria, tetanus, pertussis, poliovirus, Haemophilus influenzae type b (Hib) and pneumococcal vaccines. The 3-dose infant series of Prevnar 13 should be completed at least 60 days prior to study vaccination.

Exclusion Criteria:

* Child in care.
* Use of any investigational or non-registered product (drug or vaccine) 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 (pharmaceutical product or device).
* Chronic administration (defined as 14 or more consecutive days) of immunosuppressants, or other immune-modifying drugs during the period starting 180 days prior to the study vaccination at Visit 1 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 the day of study vaccination at Visit 1 and ending at Visit 2. Please Note:

  * Inactivated influenza (Flu) vaccine and monovalent 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 before the 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 (no laboratory testing required).
* Blood dyscrasias, leukemia, lymphomas of any type, or other malignant neoplasms affecting the bone marrow or lymphatic systems.
* 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.
* Acute disease at the time of enrollment. (Acute disease is defined as the presence of a moderate or severe illness with or without fever). Fever is defined as temperature ≥38.0°C/100.4°F by any age appropriate route. 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: a child that previously received a fourth dose of PCV-13 vaccine.