  We consider three regions with different public health conditions. In the
absence of migration among these regions, the first two have good health
conditions and the disease free state is stable; for the third region, on the
other hand, the only stable state is the endemic one. When migration is
included in the model, we assume that the second region has a disease risk that
makes its inhabitants prone to accept to be vaccinated, while the population in
the first region tends to reject the vaccination, considered riskier that the
disease. Therefore, the second region is a "buffer zone" between the two
extremal regions. We study the basic reproductive ratio as a function of the
vaccination in all regions and migration among them. This problem is studied
numerically, showing explicit situations in which migration will have an
overall positive effect in the disease dynamics, with and without vaccinations.
We also find explicit formula in the limit of small ("closed borders") and high
migration ("open borders").
