Three doses of the vaccine provides at least 99 percent protection, but in some ZIP codes fewer than two-thirds of children 5 years and younger have received that, worrying health officials.

Though many people infected with polio have no symptoms, about 4 percent will get viral meningitis and about one in 200 will become paralyzed, the health authorities say. Health authorities urged parents of children who were not yet fully vaccinated to bring them to their pediatricians.

“The risk to New Yorkers is real but the defense is so simple — get vaccinated against polio,” said Dr. Ashwin Vasan, the New York City health commissioner. “With polio circulating in our communities there is simply nothing more essential than vaccinating our children to protect them from this virus, and if you’re an unvaccinated or incompletely vaccinated adult, please choose now to get the vaccine.”