Wastewater monitoring identifies polioviruses in New York City

New York state health authorities announced Friday that polioviruses have been found in wastewater from New York City, further widening the range of areas in the state at risk of seeing polio cases.

It’s unclear if the viruses found in New York City are genetically linked to those that are circulating in Orange and Rockland counties, to the north of Manhattan. In July, state authorities announced the detection of the country’s first paralytic polio case in nearly a decade, a man in his 20s from Rockland County.

“The NYC samples didn’t contain enough genetic material to determine if they were linked to the case patient,” a spokesperson for the Centers for Disease Control and Prevention told STAT by email.

It’s possible the viruses are linked, suggesting some neighborhoods of New York are now part of a transmission network linked to Rockland and Orange counties.

“I think we don’t know for sure that they’re not linked in some sort of way to the Rockland County stuff. It’s not linked yet,” said Kim Thompson, a polio expert who is director of the not-for-profit organization Kid Risk.

Or the New York City detections could be a new importation or importations of vaccine viruses from other parts of the world.

“We live in a global society, and despite our high national vaccination coverage, it only takes only one traveler with polio to bring the disease into the U.S.,” José Romero, director of CDC’s National Center for Immunization and Respiratory Diseases, said in a statement.

Linked or unlinked, the presence of vaccine-derived viruses in sewage samples signals that there is transmission of polio in parts of New York City and in the two counties north of it, which means unvaccinated children or adults are at risk of being infected and potentially becoming paralyzed.

Most people who are infected with polio do not develop symptoms. But for the unlucky few — estimated to be between one and five people out of 1,000 infected — neurological symptoms will occur, including meningitis or paralysis.

“Polio is not gone, in spite of the fact that we’ve been able to enjoy not seeing a lot of transmission for the past couple of decades,” said Thompson. “But it’s still around and it’s still a risk and those who are unvaccinated are rolling the dice in terms of whether or not they might become infected and might become paralyzed.”

A total of six positive sewage samples were collected in June and July in New York City. The state health department did not indicate in which part of the city the positive wastewater samples were drawn and its press office had not replied to questions from STAT at the time of publication.

The viruses detected in the wastewater samples were type 2 Sabin viruses, which come from oral polio vaccine. Oral polio vaccine has not been used in the United States since 2000, which means the viruses were brought into the country in the intestinal tract of someone who had received oral vaccine elsewhere in the world, or someone who had encountered the vaccine viruses elsewhere.

The U.S. uses inactivated polio vaccine. The viruses in it have been killed, so there is no risk of those vaccine viruses circulating and infecting others. Oral poliovirus vaccines use weakened forms of the virus that, if allowed to spread in a population with low immunization rates for a prolonged period of time, can regain the power to paralyze.

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

Bassett and New York City Health Commissioner Ashwin Vasan urged people in the state who are not vaccinated to do so.

“Polio is entirely preventable and its reappearance should be a call to action for all of us,” Vasan said. “The risk to New Yorkers is real but the defense is so simple — get vaccinated against polio.”

In addition to the positive specimens in New York City, analysis of more wastewater samples from Rockland County and adjacent Orange County revealed that the vaccine viruses have been circulating in this area at least since May. The viruses in the 20 positive samples detected in the two counties are genetically linked to the virus that paralyzed the unidentified man in Rockland County.

The presence of polioviruses in this part of New York State is of serious concern to public health authorities because childhood vaccination rates in these counties are dangerously low. Rockland County was the epicenter of a large measles outbreak in 2018-2019 that centered on communities of Hasidic Jews who resist getting their children vaccinated. State health department data show that in Rockland County, only 60% of children have received the recommended three doses of polio-containing vaccine by age 2. In Orange County, the figure is 59%.

Walter Orenstein, a polio expert at Emory University, was dismayed to hear that that the viruses have been circulating in Rockland County for that long.

“If it’s detected in May, June, and July, that’s very concerning,” he said in an interview. “We don’t use oral polio vaccine and to see this much detection of type 2 [vaccine-derived] virus raises concern about whether there’s ongoing transmission of that in the U.S.”

The fact that there is virus circulating in New York City ups the ante, Orenstein suggested, because of the size of the city’s population and the potential for ongoing transmission there. He suggested the city’s health department should consider doing “stool surveys” — collecting stool specimens and checking them for polioviruses — in parts of the city where transmission is suspected to try to figure out where and among whom polioviruses are spreading.

This story has been updated with additional information.