The same strain of poliovirus that paralyzed an unvaccinated young man in New York’s Rockland County this summer is still spreading in several areas of the state as of early October, according to a wastewater surveillance study published by the Centers for Disease Control and Prevention on Friday.
The finding suggests that the virus continues to pose a serious threat to anyone in the area that is unvaccinated or under-vaccinated. The three counties with sustained transmission—Rockland, Orange, and Sullivan—have pockets of alarmingly low vaccination rates.
In Rockland, for instance, one county zip code has a polio vaccination rate among children under 2 years old of just 37 percent, according to state data. In Orange, a zip code has a vaccination rate of just 31 percent. County-wide vaccination rates of Rockland and Orange are 60 percent and about 59 percent, respectively.
Sullivan County hasn’t provided the state with zip code-level vaccination rate data. But in a press release from August, the county’s Public Health Director, Nancy McGraw, suggested some areas of the county have low rates similar to Rockland and Orange.
“Sullivan County has an overall 62.33 percent vaccination rate for polio, but there are some areas of the County with lower vaccination rates, and because polio can spread very easily, it’s important that everyone is vaccinated,” McGraw said at the time. “Public Health is offering a safe and proven vaccine available to children two months of age or older. We are working with the State to get vaccine to providers for adults. If adults need vaccine, we encourage then [sic] to contact their healthcare provider.”
Most adults and children in the US are vaccinated against polio. Since 2000, the country has relied on 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. Just the first three doses are 99 percent to 100 percent effective at preventing paralytic disease, though, and vaccination coverage rates report the percentage of 2-year-olds that have followed the recommended vaccination schedule for the first three shots.
Assessing risk
But, in pockets of low vaccination, such as those in several counties in New York, poliovirus—in this case, a revertant virus derived from an oral vaccine used abroad that transmitted among unvaccinated people—can continue spreading. In the CDC’s new study out today, health officials sifted through sewage surveillance data to see where and how extensive that spread is.
They looked for poliovirus among 1,076 samples taken from 48 sewersheds serving Rockland and 12 surrounding counties between March 9, 2022, to October 11, 2022. In all, 89 (about 8 percent) samples taken from 10 sewersheds tested positive for the poliovirus. Of the 89 samples, 82 were from counties outside of New York City, taken from sewersheds in Nassau, Orange, Rockland, and Sullivan counties. Of those 82 positive samples, 81 were genetically linked to the Rockland County patient, and one, which was from Orange county, didn’t have adequate enough genetic data to determine linkage.
The remaining seven of the 89 positive samples were from New York City, one of which was linked to the Rockland case, and five were of inadequate quality to determine linkage. Interestingly, one was of a different poliovirus that was not linked to the Rockland case, suggesting more than one strain of poliovirus was introduced to the US.
The strain of poliovirus in the Rockland case has been genetically linked to viruses spreading in London and Israel.
The fact that samples as recent as October 4, 5, and 6 tested positive for the poliovirus that has already paralyzed one person, suggests that others are still at risk in the US.
“[A]ny unvaccinated or undervaccinated adult or child living or working in Kings, Orange, Queens, Rockland, or Sullivan counties, New York should complete the IPV series now,” the authors of the study concluded.