Polio may have been spreading in New York since April

Polio may have been rampant for a year and was present in New York’s sewage as early as April, according to a new report from the Centers for Disease Control and Prevention.

A sewage sample collected in Orange County, NY in April tested positive for the virus, supplanting the area’s earliest known detection. Officials previously announced that the virus had been found in sewage samples from May in neighboring Rockland County.

Changes in the genome of the virus suggest this version has been circulating somewhere in the world for up to a year. Genetically similar versions of the virus were detected in Israel in March and in the UK in June.

The new study provides more details from an ongoing investigation into a polio case that was discovered in New York last month when officials announced a young adult in Rockland County was paralyzed by polio. It was the first polio report in the United States since 2013.

The findings aren’t entirely surprising, especially given that polio, which is highly contagious, often spreads without causing serious symptoms, said Joseph Eisenberg, an infectious disease epidemiologist at the University of Michigan. “It can be pretty widespread and go under the radar before you actually see cases of paralysis,” he said.

Officials had previously warned that the Rockland County patient was most likely the “tip of the iceberg.”

Polio immunization coverage is as low as 37 percent in some county ZIP codes, the new study found.

The patient, who had not been vaccinated against polio, was hospitalized in June after developing symptoms including fever, neck stiffness and lower-limb weakness, according to the study. The polio virus, which mainly spreads through faeces, was then detected in the patient’s stool.

Genome sequencing revealed the patient was infected with a version of the virus derived from the oral polio vaccine, which contains a weakened version of the virus. The oral vaccine has not been used in the United States since 2000. (American children are routinely immunized with an injected vaccine.)

The oral vaccine is safe and effective, but people who get it can shed the weakened virus in their stools for weeks, potentially infecting others. In communities with many unvaccinated people, the virus can continue to circulate and eventually acquire enough mutations to become dangerous again.

The discovery of the Rockland case prompted health experts to begin examining sewage samples collected in the area, including those previously collected to monitor for the coronavirus.

Officials previously announced they had found the virus in 20 sewage samples collected in Rockland and Orange counties, all of which were genetically linked to the patient sample.

The new study found that a 21st sample taken in Orange County in April also tested positive for the virus. However, not enough genomic information was available to conclusively link them to the other samples.

As of Aug. 10, 260 sewage samples from Rockland and Orange Counties had been tested, and polio was detected in 8 percent of them, according to the new study.

“This suggests many communities are staying under the radar,” John Dennehy, a virologist and wastewater monitoring expert at Queens College, said in an email.

The virus was also found in six sewage samples from New York City.

The Rockland County patient was most likely exposed to polio one to three weeks before developing symptoms, the report said. The patient did not travel abroad during this time, but attended “a large gathering,” according to the study.

Polio was detected in Rockland County sewage 25 days before the patient developed symptoms, suggesting others had previously been infected.

“The fact that we saw it in the sewage 25 days ago means it’s probably not even the second case,” said Dr. Eisenberg.

People who have received three doses of the inactivated polio vaccine are well protected against the virus, but the virus poses a potential risk to unvaccinated people, including children who are too young to be vaccinated.

Nationally, polio vaccination rates are relatively high. But there are parts of the country, including New York, where vaccination rates are much lower and the pandemic has thrown back child vaccination campaigns.

As of July 2020, just 67 percent of Rockland County children older than 24 months had received three doses of the polio vaccine, a number that has fallen to 60 percent as of this month, according to the study.

After Rockland County’s case was discovered, the local health department launched a vaccination campaign, but the number of shots given “was not enough to significantly increase vaccination rates,” the researchers reported.

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