[wat10000]

Measles is unbelievably infectious. An unvaccinated person has a 90% chance of getting infected if exposed. The virus can survive in the air for hours. In a susceptible population, one infected person will typically infect a dozen other people or more.

Changing the rate of immigration won't make a bit of difference for a disease like this. It only takes one infection in a susceptible population, and then it's game over. Unless your controls are 100% effective (including tourists and returning citizens), the only way to prevent an outbreak is for the vast majority of your people to be uninfectable.

An insufficiently vaccinated population is like a can of food. It might take longer to spoil if there's a pinhole in the side versus if you just crack it open, but it will spoil if there's any breach whatsoever.

So unless you propose to isolate to a degree more extreme than North Korea, blaming immigrants is just bigotry.