Immigrants and travelers are the source of the measles, NOT the anti-Vaxxers!
This particular case is one where the groups actually intersect.
The ultra-Orthodox Jews described here probably could have lived outside the public eye for decades even though they never got any vaccinations against measles. What disrupted this whole thing was the frequent travels of some of them between the U.S. and Israel. Once a single traveler was exposed to measles in the Middle East and brought it back to New York City, the entire community of unvaccinated people was at risk.