I doubted this initially, but you're right about the Polio epidemic. It was initially introduced by someone who received an oral vaccine abroad, and then it spread to unvaccinated individuals in the NY area:
"In July, public-health officials confirmed the first case of polio in New York State in close to a decade. The infected individual was unvaccinated for polio, contrary to New York’s recommended childhood vaccine schedule and school requirements.
The patient seems to have been infected with a vaccine-derived strain of polio, which means they were likely infected by someone who received an oral vaccine (via mouth drops) abroad (the U.S. retired oral vaccines in 2000, and currently administers them through injection). The oral vaccine uses an active (albeit weakened) virus, whereas the injection uses inactive virus; this means that people who receive the oral vaccine can occasionally infect unvaccinated individuals."
