I agree it’s a concern, just as similar resurgence of some contagious diseases is in the U.S. Unfortunately, many people haven’t been vaccinated for what were (until recently) the standard contagious illnesses, because they believed there was no risk of exposure to the disease. Oops.
Vaccination rates are definitely part of the equation, and I have no doubt that some parents are still avoiding them because of the reasons you cite as well as a now-debunked scare as suggested in the article, but I don't think that it's entirely inappropriate to consider the possibility that some if not a substantial number of third-world immigrants do not get vaccinated because of basic ignorance to the benefits of vaccinations, a religious or cultural impasse or a general fear and distrust of Western medicine, which brings us back to immigration. If you bring in enough third-worlders, you're going to get a certain percentage that are ignorant, fearful or both.