ABOVE: Centers for Disease Control and Prevention

Update (September 9): New York’s Governor Kathy Hochul declared the state’s polio outbreak to be a disaster today, a move intended to boost vaccination rates and help contain the virus.

New York State and City health departments issued a statement on Friday (August 12) notifying residents that poliovirus—the virus that causes polio—was detected in the New York City’s wastewater, suggesting it is circulating locally. 

Though the exact locations of the positive samples have not been disclosed, the New York State Department of Health  reports six samples of concern (two in June, and four in July). Poliovirus had already been detected in the wastewater systems of nearby Orange and Rockland counties back in May, reports The New York Times, and its presence in New York City comes three weeks after a confirmed case of polio in a 20-year-old man from Rockland County. 

“The detection of poliovirus in wastewater samples in New York City is alarming, but not surprising,” State Health Commissioner Dr. Mary T. Bassett says in the announcement. “Already, the State Health Department—working with local and federal partners—is responding urgently, continuing case investigation and aggressively assessing spread.” 

According to the US Centers for Disease Control and Prevention (CDC), polio is highly contagious, only infects humans, and is primarily spread via contact with fecal matter; however, the agency notes a less common transmission route is via droplets expelled when a person with the virus sneezes or coughs. Most people infected by the poliovirus exhibit no symptoms, about a quarter experience flu-like symptoms, and between 1 and 5 percent of people develop meningitis (swelling in membranes that surround the brain and spinal cord). In severe cases, as with the man from Rockland county, paralysis develops: The CDC estimates this occurs in 1 out of every 200 to 2,000 people who acquire the virus, and there is no treatment. Between 2 and 10 percent of the people who experience paralysis die when muscles that assist breathing stop functioning.

Most Americans have been vaccinated against the virus, and a recent study found that 90 percent of adults between the ages of 40 and 49 had protective antibodies, the Associated Press reports; about 93 percent of children in the US have received three of the four recommended vaccine doses. In contrast, the New York health departments’ statement reports the percentage of children who’ve received three vaccine doses in Orange County, Rockland County, and New York City is around 59 percent, 60 percent, and 86 percent, respectively.

In the statement, New York City Health Commissioner Ashwin Vasan urges unvaccinated residents to act: “The risk to New Yorkers is real but the defense is so simple—get vaccinated against polio.”