A Safety and Immune Study of 2 Types of GlaxoSmithKline's Varicella Vaccines Given as a 2-doses Course to Healthy Children 12-23 Months of Age.

The purpose of this study is to evaluate the safety and immunogenicity of 2 formulations of GSK Biologicals' varicella vaccines given as a 2-dose course in the second year of life.

GSK Biologicals has removed human serum albumin (a stabilizer) from its varicella vaccine to minimize as much as possible the use of animal or human-derived products in the production of vaccines. The study is intended to provide information on the safety and immunogenicity of GlaxoSmithKline (GSK) Biologicals' candidate varicella vaccine formulated without human serum albumin (HSA) in contrast to Varilrix™ (GSK) which contains HSA when both are used in a two-dose schedule, with the first and second doses given approximately 42 days apart in the second year of life.

The immunogenicity sub-cohort will be comprised of approximately 400 subjects, representing approximately 100 subjects enrolled in each of the participating countries.

Rationale for amendment 1: Sites in the UK can perform home visits. For subjects participating through home visits, the subject's parent(s) / Legally Acceptable Representative(s) \[LAR(s)\] will be requested to sign a Recruitment/Randomisation agreement to provide personal information and to agree to have their child randomised before providing written consent to participate in the study (to be provided at the 1st home visit).

Eligibility Criteria:
Inclusion Criteria:

* Subjects' parent(s)/ LAR(s) who, in the opinion of the investigator, can and will comply with the requirements of the protocol.
* A male or female between, and including, 12 and 23 months of age (i.e. 12 months to a day before 24 months) at the time of the first study vaccination.
* Written informed consent obtained from the parent(s)/LAR(s) of the subject prior to performing any study specific procedure.
* Subjects in stable health as determined by investigator's clinical examination and assessment of subject's medical history.
* Subjects must have had prior administration of a dose of measles, mumps and rubella (MMR) vaccine at least 30 days (Day -31 or earlier) prior to study vaccination at Day 0.

Exclusion Criteria:

* Child in care.
* Use of any investigational or non-registered product other than the study vaccines during the period starting 30 days before the day of study vaccination (i.e., 30 days prior to Visit 1/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 (defined as 14 or more consecutive days) 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 live viral vaccine not foreseen by the study protocol during the period starting 30 days prior to study vaccination at Visit 1/Day 0 until study end. Non study live viral vaccines can be administered at Visit 3 (Day 84) after completion of study procedures.
* Planned administration/ administration of an inactivated vaccine not foreseen by the study protocol during the period starting 7 days prior to each vaccination (at Visit 1/Day 0 and Visit 2/Day 42) and ending 14 days after each vaccination. Outside of this period, non-study inactivated vaccines can be administered as per standard of care.
* Administration of immunoglobulins and/or any blood products during the period starting 180 days prior to the first vaccine dose or planned administration from the date of first study vaccination through the entire study.
* History of varicella or zoster.
* Known exposure to varicella/zoster during the period starting within 30 days prior to first study vaccination.
* Previous vaccination against varicella.
* Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history and physical examination (no laboratory testing required).
* Subjects with blood dyscrasias, leukemia, and lymphomas of any type.
* 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 or latex.
* Major congenital defects or serious chronic illness.
* Acute disease and/or fever at the time of enrolment.

  * Fever is defined as temperature ≥38. 0°C/100.4°F by any age appropriate route.
  * Subjects with a minor illness without fever may be enrolled at the discretion of the investigator.
* 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.