Health officials announced Friday that polio has been detected in wastewater samples in New York City.
It comes just a few weeks after a case of polio was detected in Rockland County, located north of the city.
The New York State Department of Health and the New York City Department of Health and Mental Hygiene said the polio virus is likely circulating locally.
"For every one case of paralytic polio identified, hundreds more may be undetected," State Health Commissioner Dr. Mary Bassett said in a statement. "The detection of poliovirus in wastewater samples in New York City is alarming, but not surprising."
She continued, "Already, the State Health Department -- working with local and federal partners -- is responding urgently, continuing case investigation and aggressively assessing spread. The best way to keep adults and children polio-free is through safe and effective immunization -- New Yorkers' greatest protection against the worst outcomes of polio, including permanent paralysis and even death."
On July 21, the NYSDOH revealed a patient in Rockland County had contracted a case of vaccine-derived polio, the first case in the United States in nearly a decade.
Since then, it's been revealed the patient was a previously healthy 20-year-old man. He was diagnosed after he went to the hospital when he developed paralysis in his legs.
As of Aug. 12, 20 wastewater samples were genetically linked to the Rockland County patient including 13 samples collected in May, June and July from Rockland County and seven samples collected in June and July from nearby Orange County, health department data shows.
Officials have stressed the importance of getting vaccinated against or staying up-to-date with the immunization schedule. Among unvaccinated people, polio can lead to permanent paralysis in the arms and/or legs and even death.
The statewide rate of polio vaccination -- excluding New York City -- is 78.96% among those who have received at least three doses, state data shows. The Rockland County rate sits at 60.34%. In Orange County, the rate is even lower at 58.66%.
In New York City, 86.2% of children aged 6 months to 5 years have received three doses of the polio vaccine, according to government data. Among the boroughs, Manhattan has the highest rate at 91% while Staten Island has the lowest rate at 81.7%.
"The risk to New Yorkers is real but the defense is so simple -- get vaccinated against polio," City Health Commissioner Dr. Ashwin Vasan said in a statement. "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. Polio is entirely preventable and its reappearance should be a call to action for all of us."
The inactivated poliovirus vaccine, the only vaccine currently used in the U.S., protects 99% of children who get all four recommended doses from polio infection. The vaccine is mandated to attend public schools in New York.
State health officials said the majority of adults do not need the polio vaccine or a booster because they were already vaccinated as children.
It is, however, recommended adults receive one lifetime booster if they are traveling to an area with widespread polio transmission.