Immunogenicity and Safety Study of GlaxoSmithKline (GSK) Biologicals' Combined Measles-mumps-rubella (MMR) Vaccine in Subjects Four to Six Years of Age

The purpose of this study is to support licensure of GSK Biologicals' MMR vaccine (Priorix®) in the US by generating immunogenicity and safety data in contrast to the US standard of care, Merck's MMR vaccine (M-M-R®II), when given as a second dose to children four to six years of age.

The GSK Biologicals' MMR vaccine (Priorix®) and Merck's MMR vaccine (M-M-R®II) are referred to as Inv_MMR vaccine and Com_MMR vaccine respectively. 2 lots of the comparator vaccine (Com_MMR_L1 and Com_MMR_L2) will be used, but the 2 lots will be analysed as a pool.

The Inv_MMR vaccine will be administered as a second dose to children who already received a first dose Com_MMR vaccine. Since the second dose of a MMR vaccine in the US is routinely co-administered with DTaP-IPV vaccine (Kinrix®) and varicella vaccine (VV) (ProQuad® or Varivax®), some children will receive one dose of these vaccines along with either of the MMR vaccines.

Eligibility Criteria:
Inclusion Criteria:

* Subjects who the investigator believes that they and/or their parent(s) or LAR/s can and will comply with the requirements of the protocol.
* Male or female subjects 4 to 6 years of age at the time of vaccination.
* Written informed consent is obtained from the parent(s)/LAR(s) of the subject (assent will be obtained from subjects in line with local rules and regulations).
* Subjects in stable health as determined by investigator's physical examination and assessment of subjects' medical history.
* Subjects received either a single dose of M-M-R II, M-M-R VaxPro or ProQuad in the second year of life.
* For subjects enrolled in the sub-cohort receiving co-administered DTaP-IPV and VV:

  * subjects received previous DTaP vaccine doses with INFANRIX® and/or PEDIARIX® for the first three doses and INFANRIX® for the fourth dose of the DTaP-containing vaccine.
  * subjects received a first dose of VV in the second year of life.

Exclusion Criteria:

* Child in care.
* Use of any investigational or non-registered product other than the study vaccine during the period starting 30 days before the day of study vaccination/s or planned during the entire study period.
* Previous vaccination with a second dose of measles, mumps, rubella containing vaccine/s.
* Chronic administration of immunosuppressants or other immune-modifying drugs during the period starting 180 days prior to Day 0 or any planned administration of immunosuppressive and immune-modifying drugs during the entire study. Inhaled and topical steroids are allowed.
* Administration of immunoglobulins and/or any blood products during the period starting 180 days before entering the study or planned administration from the date of vaccination through the immunogenicity evaluation at Visit 2.
* Planned administration/ administration of a vaccine not foreseen by the study protocol during the period starting 30 days prior to the study vaccination/s and ending 42 days after the vaccination/s (at Visit 2), with the exception of live intranasal or inactivated influenza (flu) vaccine, which may be given at any time during the study, including the day of study vaccination/s. Inactivated influenza vaccine must be administered at a different location from the study vaccine. Any age appropriate vaccine may be given starting at Visit 2, and anytime thereafter.
* 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.
* History of measles, mumps, and/or rubella disease.
* Known exposure to measles, mumps and/or rubella during the period starting 30 days prior to enrollment.
* Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history and physical examination.
* History of allergic disease or reactions likely to be exacerbated by any component of the vaccine(s), including systemic hypersensitivity to neomycin 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. Acute disease is defined as the presence of a moderate or severe illness with or without fever. Fever is defined as temperature ≥38°C (100.4°F) measured 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 according to the subject's medical history.
* Any other condition which, in the opinion of the investigator, prevents the subject from participating in the study.

In addition, for subjects enrolled in the sub-cohort receiving co-administered DTaP-IPV+VV:

* Previous vaccination with a second dose of varicella-containing vaccine.
* Receipt of any varicella-containing vaccine during the period starting 90 days before the day of study vaccination.
* History of varicella/zoster disease.
* Known exposure to varicella/zoster during the period starting 30 days prior to enrollment.
* History of diphtheria, tetanus, pertussis, and/or poliomyelitis disease.
* Vaccination against diphtheria, tetanus, pertussis or polio given after the second year of life.
* Occurrence of transient thrombocytopenia or neurological complications following an earlier immunization against diphtheria and/or tetanus toxoids.
* Following a previous administration of DTP vaccine: temperature ≥40.6°C (\>105°F) during the period starting 48 hours not due to another identifiable cause, collapse or shock-like state during the period starting 48 hours, persistent, inconsolable crying lasting three hours or more within 48 hours, seizures with or without fever occurring during the period starting three days, or encephalopathy of unknown aetiology occurring during the period starting 7 days of a previous administration of DTP vaccine.
* Hypersensitivity reaction to any component of the DTaP-IPV and/or varicella vaccines.