The MMR vaccine is what people should get. It's been around for decades.
But as you said, there's no treatment for measles, so if you didn't get vaccinated and get measles, you're SOL. It's not like you can get the MMR at that point.
And I have little doubt the vast majority of those who were unvaccinated were illegals. While those who were vaccinated weren't...and yet still got measles.