As measles-mumps-rubella (MMR) vaccination is established as routine childhood practice in most industrialised countries and varicella vaccination is now being introduced in many countries during the second year of life, a combined measles-mumps-rubella-varicella vaccine was developed for administration convenience and improved compliance to vaccination. To account for situations where children have received a first dose of MMR vaccine without varicella, this study will evaluate the effect of the combined measles-mumps-rubella-varicella vaccine given in place of the second dose of MMR vaccine. A second dose of the monovalent varicella vaccine will be given to all children participating to this trial since there is a current debate on the need of a second dose to induce a full protection against varicella.

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.

Patient-level data for this study will be made available through www.clinicalstudydatarequest.com following the timelines and process described on this site.