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The same strain of the polio virus paralyzed an unvaccinated young man in Rockland County, New York this summer, still spreading to several areas of the state as of early October waste water research released by the Centers for Disease Control and Prevention on Friday.

The finding suggests the virus continues to pose a serious threat to those in the area who are unvaccinated or undervaccinated. In the three counties with persistent transmission—Rockland, Orange, and Sullivan—vaccination rates are alarmingly low.

In Rockland, for example, the polio vaccination rate among children under 2 years old is just 37 percent in one county zip code, data of the state. In the Orange zip code, the vaccination rate is just 31 percent. Rockland and Orange county vaccination rates are 60 percent and about 59 percent, respectively.

Sullivan County did not provide data on vaccination rates by zip code to the state. But in press release from Augustcounty health director Nancy McGraw suggested that some areas of the county have rates similar to Rockland and Orange.

“The overall polio vaccination rate in Sullivan County is 62.33 percent, but there are some areas of the county with lower vaccination rates, and because polio can spread so easily, it’s critical that everyone be vaccinated,” McGraw said at the time. “Healthcare offers a safe and proven vaccine available to children two months of age and older. We are working with the state to provide the vaccine to adult providers. If adults need the vaccine, we encourage it [sic] contact your healthcare provider.”

Most adults and children in the US are vaccinated against polio. Since 2000, the country has relied on the inactivated polio vaccine (IPV), which is given in three doses before the age of 24 months, with a fourth shot between the ages of 4 and 6. The first three doses alone are 99 percent to 100 percent effective in preventing polio, but vaccination coverage rates show the percentage of 2-year-olds who followed the recommended vaccination schedule for the first three shots.

Risk assessment

But in low-vaccination hotspots, such as several counties in New York, poliovirus—in this case, a revertant virus derived from an oral vaccine used overseas and transmitted among unvaccinated people—can continue to spread. In a new CDC study released today, health officials looked at wastewater surveillance data to find out where and how widespread it is.

They looked for poliovirus among 1,076 samples taken from 48 sewage sheds serving Rockland and 12 surrounding counties between March 9, 2022 and October 11, 2022. A total of 89 (about 8 percent) samples taken from 10 sewage sheds yielded a positive result for poliovirus. Of the 89 samples, 82 were from counties outside of New York, collected from sewage sheds in Nassau, Orange, Rockland, and Sullivan counties. Of those 82 positive samples, 81 were genetically related to a patient from Rockland County, and one from Orange County did not have enough genetic data to determine a relationship.

The remaining seven of the 89 positive samples were from New York, one of which was linked to the Rockland case, and five of which were of insufficient quality to determine a link. Interestingly, one was from a different polio virus that was not linked to the Rockland case, suggesting that more than one strain of polio virus was introduced into the United States.

The polio strain in Rockland’s case was genetically linked to the spread of the viruses London and Israel.

The fact that samples taken on October 4, 5 and 6 tested positive for polio, which has already paralyzed one person, suggests others are still at risk in the US.

“[A]All unvaccinated or undervaccinated adults or children living or working in Kings, Orange, Queens, Rockland, or Sullivan counties, New York should complete the IPV series now,” the study authors concluded.