The MMR vaccine does not give full immunity(the reason booster shots exist), immigrants can enter the country while carrying the disease, and sometimes live virus vaccines like MMR can leave the people who get them contagious. The only ways to have zero cases of any disease in the country are to either eradicate it globally (like small pox), or to eradicate it nationally and prevent cross border transmission (like polio).

I can't possibly explain the mechanics of disease eradication without mentioning the movement of infected people. I don't want to get reported for bigotry though so I should simply have not replied on this topic to guarantee my continued use of this site. Unfortunately that means all the discussions here are partial. The ability of hacker news users to educate themselves with discussion is severely limited by the self censorship you impose on us. The fact you completely misunderstood what I said is not surprising as you likely choose to live in a censored world of partial arguments that leave you ignorant, uneducated, and comfortably numb. I would still never report you though.

Nothing in the post stated that immigrants are a major source of MMR, only that stopping cross border transmission is a requirement for effective eradication.