For contagious diseases like measles a successful immunization program can result in herd protection. Small outbreaks may still occur but fade out soon, because the possibilities for the pathogen to spread in the ‘herd’ are very small. This implies that people who refuse to participate in such a program will still benefit from the protection it offers, but they don’t do their part in maintaining protection. Isn’t that a case of freeriding—and isn’t that unfair towards all the people who do collaborate? If so, that might be considered an additional ground for making vaccination mandatory or compulsory.In this paper I argue that vaccination refusal can be considered as freeriding, but that this might not be unfair. The public good of herd protection is a peculiar public good because it supervenes on private benefits that are enjoyed by all who do opt for vaccination. For vaccinated individuals, the additional benefit of herd protection comes about, as it were, for free, and hence they can’t complain that others benefit without sharing in the burdens. There are however still other grounds for making vaccination compulsory or at least for seeing refusal as a morally wrong choice.