New York Governor Kathy Hochul declared a state disaster emergency on Friday after samples of the polio virus were discovered in wastewater in three counties outside of New York City.
Hochul's executive order came more than a month after an adult in Rockland County, north of New York City, was diagnosed with the disease in July.
It was the first confirmed case of polio in the United States in nearly a decade.
The declaration would expand the number of people authorised to administer polio vaccines and other steps to accelerate inoculation rates.
The state of emergency will stay in effect until October 9.
The polio virus was present in wastewater samples collected as early as April, Hochul's executive order said.
Virus was detected in wastewater samples taken in Orange, Rockland and Sullivan counties every month since April, indicating the virus was present in the state before the Rockland County case was found in July.
After the disease was detected, New York officials began urging unvaccinated residents to get polio vacations.
While people of all ages are under threat, the virus primarily affects children aged three and younger.
Polio can cause irreversible paralysis in some cases, but it can be prevented by a vaccine first made available in 1955.
There is no known cure. Three injections of the vaccine provide nearly 100 per cent immunity.
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