A new study from the C.D.C. provides more details about a polio case detected in New York last month, and suggests the virus has been spreading elsewhere for a year.
Health officials in Rockland County offered pop-up polio vaccinations and urged the public to get shots as they investigated whether the disease had spread to others.
An adult who lives in Rockland County was infected by someone who received the oral polio vaccine, which is no longer used in the United States, officials said.