"In all three of these outbreaks, someone who had not been vaccinated traveled overseas and brought the disease back with them"
One thing seems obvious to me. Ban our CITIZENS from reentering the US unless they can show that ALL of their vaccinations are current. We could delay reentry to the US by quarantining them in a place similar to Ellis Island for 21 days (or some suitable time) to make sure they were not carrying in a disease. Those people that have religious, moral (or just plain stupidity in the case of vaxers) could avoid the vaccinations by just being sequestered.
NOTE: Quarantining is not incarceration and has been proven legal such as in the case of "Typhoid Mary" and quarantining by the health department. I don't see any legal problems but IANAL.