As reported in a recent issue of Eurosurveillance, a mumps outbreak is ongoing in the Netherlands despite high vaccination coverage of 90-95% [1]. The reported mumps cases are restricted to geographic regions with a high percentage of residents who are members of a religious community that rejects vaccination. Consequently, two thirds of the mumps patients were not vaccinated. However, also vaccinated individuals in these regions were affected [1]. Since 1987, the measles-mumps-rubella (MMR) combination vaccine produced by the Netherlands Vaccine Institute (NVI) is part of the Dutch national immunisation programme and administered at the ages of 14 months and nine years.