“Polio gets reintroduced by immigration, it has a fecal-oral vector. You would need to come in contact with fecal matter and ingest it. Like swimming in a lake where lots of infected people have been. Or changing the diaper of a baby that received the live vaccine”
Or. . . infected illegals working in kitchens and not practicing proper hygiene. Typhoid Mary, anyone?
I don't like to think about that one.