Measles is a vaccine-preventable disease, which can be life-threatening in immunosuppressed children. Currently, measles vaccine is not recommended in pediatric orthotopic liver transplant recipients, because it is a live-attenuated vaccine.

We want to assess the influence of immunosuppression on immunity against measles in previously vaccinated children and to evaluate the induction of B cell and T cell response against measles elicited by vaccination in children at least 12 months after transplantation.

Eligible children in Group 2 will receive a standard dose (0.5 ml) of MMR vaccine during the first medical visit (V1). The lot number and the expiration date will both be recorded on the patient's case report form (CRF). A serological evaluation 4-8 weeks after MMR will identify children requiring an additional dose given 1-2 months apart, as currently recommended for subjects 1 year-old or with limited immune competence (i.e. HIV-infected children). Serological evaluation 4-8 weeks after the second dose or at the one-year follow-up will identify eventual non-responder requiring a third dose. Three will be the maximal number of administrated dose according to this protocol. The persistence of measles-specific antibodies will be assessed yearly, when patients come for their routine visit to the transplant center.

Children who do not need MMR immunization because of protective levels will be monitored yearly for maintenance of antibody levels during routine yearly visits/ blood samplings and will not have further intervention.

Inclusion Criteria:

• Age ≥ 12 months
• Measles-specific IgG antibodies negative (<0.2 IU/L), as detected by the routine ELISA assay
• ≥ 12 months from the time of transplantation and ≥ 2 months from the time of an acute rejection episode
• Steroids < 2 mg/kg/day, tacrolimus < 0.3mg/kg/day and tacrolimus level < 8 ng/ml for > 1 month.
• Total lymphocyte count ≥ 750 cells/ul at time of immunization

Exclusion Criteria:

• Known wild-type measles exposure during the last four weeks
• Measles-containing immunoglobulins administered within the 5 months preceding the measles vaccine. If the child receives measles-containing Ig before an additional dose of MMR vaccine, he/she will be withdrawn from the study
• Antiviral agents administered during the last four weeks
• Febrile illness (>38.5°) in the 72 hours before vaccine administration
• Chronic aspirin therapy
• Any other immunization with a live-attenuated vaccine during the last four weeks
• Pregnancy