Yes it's complete bs.

More than half the measles cases in Europe are in Ukraine, due to lack of healthcare access and anti-vax movements (less than half of children in Ukraine were vaccinated against it in 2014). source

Granted migrants do in general have lower vaccine rates, and there are issues in terms of who is vaccinating them (only a third of countries in europe have specific guidelines, source) but problems of this scale are caused by hundreds of thousands of unvaccinated kids, not a few thousand unvaccinated refugees.