EXPLAINER: What to Know About Polio Spreading in New York

The polio virus has been found in New York City sewage, but officials are stressing that the highest risk is for people who haven’t been vaccinated. Polio was once one of the nation’s most feared diseases, with annual outbreaks causing thousands of cases of paralysis. Its elimination in the U.S., officially declared in 1979, is considered one of the nation’s greatest public health victories. Yet cases have cropped up occasionally since then, often among people who had traveled to other countries. Recently, an unvaccinated young adult north of New York City contracted polio. On Friday...