A sewage sample collected in April in Orange County, New York, tested positive for the virus, overturning the earliest known detection in the area. Officials had previously announced that the virus had been found in sewage samples dating back to May in neighboring Rockland County. Changes in the virus’s genome suggest that 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 Britain in June. The new study provides more details from an ongoing investigation into a case of polio that was identified in New York last month, when officials announced that a young adult in Rockland County had been paralyzed by polio. It was the first report of polio in the United States since 2013. The findings are not surprising, especially since 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 circulate quite extensively, being under the radar, before you actually start seeing cases of paralysis,” he said. Officials had previously warned that the Rockland County patient was likely the “tip of the iceberg.” In at least one of the county’s ZIP codes, just 37 percent of children under 24 months old have received three doses of the polio vaccine, according to the new study. The patient, who had not been vaccinated against polio, was admitted to the hospital in June after developing symptoms including fever, neck stiffness and lower limb weakness, according to the study. The polio virus, which is spread primarily through feces, was subsequently found in the patient’s feces. Genomic sequencing revealed that the patient was infected with a version of the virus derived from the oral polio vaccine, which contains an attenuated version of the virus. The oral vaccine has not been used in the United States since 2000. (American children are routinely immunized with an injectable vaccine.) The oral vaccine is safe and effective, but people who receive it can shed the weakened virus in their stool 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 testing sewage samples collected in the area, including those previously collected for coronavirus surveillance. Officials had previously announced that they had found the virus in 20 samples of sewage collected in Rockland and Orange counties, and that all had been genetically linked to the patient sample. The new study revealed that a 21st sample, collected in Orange County in April, also tested positive for the virus. However, there was not enough genomic information available to definitively link them to the other samples. Two hundred sixty samples of sewage from Rockland and Orange counties had been tested as of Aug. 10, and polio was detected in 8 percent of them, according to the new study. “This suggests that there is a lot of community spread under the radar,” John Dennehy, a virologist and wastewater surveillance expert at Queens College, said in an email. The virus has also been found in six sewage samples from New York City. The Rockland County patient was likely exposed to polio one to three weeks before developing symptoms, the report noted. The patient did not travel abroad during that time, but attended “a large gathering,” according to the study. Polio was detected in sewage in Rockland County 25 days before the patient developed symptoms, suggesting others had been infected in the past. “The fact that we’re seeing 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 is 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 pockets of the country, including New York, where vaccination rates are much lower and the pandemic has delayed childhood vaccination campaigns. As of July 2020, just 67 percent of Rockland County children under 24 months old had received three doses of the polio vaccine, a rate that dropped to 60 percent this month, the study found. After the Rockland County case was identified, the local Health Department launched a vaccination campaign, but the number of shots given was “not sufficient to significantly increase” vaccination rates, the researchers said.
