HMM: How polio came back to New York for the first time in decades, silently spread and left a patient paralyzed. “How polio reemerged in New York this year remains the subject of investigation, but public health officials believe the virus originated overseas in a country that still uses the oral polio vaccine. American health officials stopped using the oral vaccine more than 20 years ago because it contains live virus that can — in rare circumstances — mutate to become virulent, but it is still common in other countries.”