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.