There are small outbreaks in lots of countries now and again. Combination of international travel and patchy vaccine coverage causes that.

The difference with Afghanistan, Nigeria and Pakistan is that it is endemic at least in parts of the countries, meaning it is regularly found in the population and that it is self-sustained. Elsewhere the outbreaks are sporadic and isolated enough that they die back.

There was an outbreak in the USA in 2005 though no one suffered permanent damage: http://www.nytimes.com/2005/11/08/health/08iht-polio.html?pa...