So- it surely would have spread if infected immigrants traveled to other cities.

So where is the evidence that this actually occurred?

You answered your question in your first sentence

No, LM. You are suffering a failure to follow an argument-

I asked you to provide proof that the disease spread.

Such proof would be found in cases of measles discovered in immigrants who traveled to those other cities you mentioned.

Now.... Increasingly I will agree with you..... as the CDC under RFKJr continues to muddy its recommendations regarding vaccines and vaccination rates continue to fall as a result, transmission of the disease within the population at large will continue to increase, as it is right now.

And it makes no difference whether the vector for that transmission is an unvaccinated immigrant coming in from Mexico, an unvaccinated schoolchild in North Carolina, or an unvaccinated businessman flying back from a meeting in Calcutta.