During a 12 month follow-up period the investigators will register disease activity and side-effects at different moments in time to determine safety of vaccination. The efficacy of the vaccine will be studied according to antibody levels and function against measles, mumps and rubella in the blood. Tregs will be isolated and their functionality will be determined using the blood cells collected during follow-up. This enables us to study the role influence of vaccination on regulatory mechanisms in our immune system.