The New York City Health Department said on Friday that there had been a detection of the disease in the city.
The findings were called alarming by the health commissioner. The city and New York state are being assessed for the spread of the disease.
It is possible for hundreds of more cases to be undetected if there is a safe and effective vaccine available.
The disease can cause permanent paralysis of the arms and legs. People who are not up to date with their vaccinations are being urged to get their shots.
According to health officials, the risk of an outbreak has increased because of the decline in vaccinations. A majority of New York City children who are 6 months to 5 years old have not completed their vaccinations against the disease.
The majority of children in New York City have received at least one dose of the vaccine. There are some neighborhoods in the city where less than 70% of children in this age group have received three doses of the vaccine.
Last month, New York state health officials confirmed that an unvaccinated adult in Rockland County, a suburb of New York City, caught the disease and was paralyzed. In both Rockland County and Orange County, the disease was found.
The strain of unvaccinated adult caught is related to the sewage samples in Rockland and Orange counties. The New York City metropolitan area has a local spread of the virus, but it is not clear where the chain of transmission started.
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