A measles epidemic is emerging in the Netherlands. The hunderds of cases are mainly in areas where people live who don't vaccinate their children because of religious reasons. If 90% of the people or more are vaccinated measles is not epidemic because of something that is called herd immunity. A disease like measles spread from person to person, and if enough people are vaccinated, the disease cannot spread and is not epidemic. But in certain areas in the Netherlands, there live many very religious groups, so called fundamentalists Protestants, do not vaccinate their children because of their religious beliefs. As a consequence, these areas, called the Bible belt (see figure on the right), have vaccination rates below 90%. As a consequence these areas are more vulnerable to outbreaks. This not only affect religious communities, but also young children (< 14 months), who have not yet been vaccinated are at risk. This problem shows the conflict between religious beliefs of one group affecting the health of their children and the children outside the religious groups. What is the best solution to this? Some people call to make vaccination mandatory, other argue that this can become counter productive since imposing vaccination (which is now voluntary) stimulate the anti-vaccination lobby groups. The current outbreak, which is likely to cause the lives of some of the children, is a consequences of imperfect public good provision by the community. But a solution is not obvious since different values and beliefs are involved.