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 and of varicella vaccine 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. 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.