and assuming that they are contracting other kids with it, the new "american victims" still wouldn't get it if properly vaccinated.
it's not like immigration to our country (especially border states) is some new thing. this is the EXACT reason you get vaccinated...so when you home-schooled, essential oil, non-vaxxers from utah come visit our state to spend a week at disneyland you don't get measles from the poor immigrants fleeing the drug wars in mexico to find asylum in our state since they obviously don't feel comfortable in yours.