Immunogenicity, Safety of Measles-mumps-rubella-varicella Vaccine (MeMuRu-OKA) Compared to Priorix™ Given With Varilrix™

Inclusion Criteria: * Children must be healthy to participate Exclusion Criteria: * Immunosuppressive (including HIV) conditions, allergic diseases, neurological disorders, known anaphylactic reaction to MMR vaccine, and fever (axillary temperature ³ 37.5°C at the time of vaccination) are excluding factors. * Children must have received one dose (but not more) of MMR at least 6 weeks before entering the study. * They must not receive or have received other non-registered drug or vaccine within 30 days prior to study start, or immunosuppressants for more than 14 days. * Immunoglobulins or any blood products are prohibited during the 6 months before and during the study, as well as vaccine other than that foreseen by the protocol, 30 days before until 56 days after vaccination. * Children must not have been vaccinated against varicella. * They must not have had measles, mumps, rubella or varicella, or have been exposed to those diseases within 30 days prior to study start. * New-born infants (\< 5 weeks of age), pregnant women without previous exposure to chickenpox, and immunodeficient persons cannot live in the same household as the vaccinated child.