I've heard it said before that preventable disease outbreaks like this happen because children who are typically not yet old enough to be vaccinated come into contact with a more mature individual who was never vaccinated.
If so, it seems to me that the only reason this kind of thing keeps happening is because of THEIR choice... and their choice is directly affecting the lives of other children that they could communicate the disease to.
As for how to really get them to support vaccinations? I can only suggest something that is at least mostly preventable through vaccination, but particularly virulent and lethal as what may be the only thing to have any impact. It won't necessarily convince them to do anything about it if they succumb themselves, but the memory of the incident will stick around for at least a couple of generations in the survivors.