Evaluate Vaccine Against Chickenpox and a Combined Vaccine Against 4 Viral Childhood Diseases: Measles, Mumps, Rubella and Chickenpox

An observer-blind study to evaluate GlaxoSmithKline Biologicals' live attenuated varicella vaccine and GlaxoSmithKline Biologicals' combined measles-mumps-rubella-varicella vaccine in the prevention of varicella disease in children. The Protocol Posting has been updated in order to comply with the FDA Amendment Act, Sep 2007.

According to treatment group allocation, participants will receive study vaccines and be followed for antibody titres and occurrence of varicella disease. This study is conducted in 2 phases. Phase A includes the vaccination period and an observation period for efficacy. The efficacy endpoints will be evaluated over at least two years after vaccination. During this period, the immunogenicity endpoints will be evaluated with respect to the immune response 43 days after vaccination and the persistence of antibodies over two years to varicella (for all subjects) and to measles, mumps and rubella (for a subset of subjects). Regarding the safety endpoints, SAEs (including any complicated varicella cases if observed) will be assessed for all subjects during the whole Phase A duration, whereas, solicited (local and general) and unsolicited adverse events will be assessed in a subset of subjects within a 43-day period after vaccination. Phase B is an extension of Phase A. It is a long-term follow-up until Year 10 to examine the long-term efficacy of the study vaccines against clinical varicella disease as well as the long-term persistence of antibodies to varicella (for all subjects) and to measles, mumps and rubella (in a subset of subjects) after vaccination.