From the Discover: Bad Astronomy blog
See also: http://en.wikipedia.org/wiki/Herd_immunity
How? Through vaccination.
Yup. The first reports of polio were confirmed in April — 413 of them. However, that ended in late June, when no new cases were reported. That is credited to the thousands of doctors and nurses who not only vaccinated at least 97% of the children in each region of the mountainous country, but also flooded the area with multi-lingual informational leaflets, posters, and banners.
And they succeeded! With no new reports, it appears this outbreak was stopped cold.
And with the AVN in Australia getting hammered repeatedly in the press, I can now have some hope that the movement here in the United States, spearheaded by Jenny McCarthy, will die off as well. Vaccinations work, and they save a lot of lives.