The United States has had one confirmed case of paralytic polio in the past three decades. That case occurred in 2022 in Rockland County, New York, involving an unvaccinated young adult. Before that, the last case of wild poliovirus acquired within the country was in 1979, and the last imported case of wild poliovirus was in 1993.
The 2022 New York Case
In June 2022, a young adult in Rockland County, New York, went to an emergency department after five days of low-grade fever, neck stiffness, back and abdominal pain, constipation, and two days of weakness in both legs. The patient had never been vaccinated against polio. Testing confirmed vaccine-derived poliovirus type 2 in stool samples collected about 11 days after symptoms began.
This was not wild poliovirus. It was a vaccine-derived strain, meaning it originated from the oral polio vaccine (OPV) used in other countries. The oral vaccine contains a weakened live virus that, in rare cases, can mutate as it passes through a community with low vaccination rates. Genetic sequencing showed the virus had accumulated enough mutations to suggest it had been circulating person-to-person for roughly a year, though where that transmission occurred before reaching New York is unknown.
The U.S. has used only the inactivated (injected) polio vaccine since 2000, so the vaccine-derived virus did not originate domestically. It was likely introduced through travel from a region still using the oral vaccine.
Why Cases Are So Rare
Polio vaccination coverage among U.S. children remains high. About 92% of children born in 2021 and 2022 received at least three doses of the polio vaccine by age 24 months, based on the most recent CDC immunization survey data. That level of coverage makes widespread transmission extremely unlikely, even when a case is introduced from abroad.
The 2022 case happened in a community where vaccination rates were significantly lower than the national average. Rockland County had pockets of undervaccinated populations, which is exactly the type of setting where an imported virus can gain a foothold. The CDC considers communities with less than 80% three-dose polio vaccination coverage in children to be at elevated risk.
Wild Poliovirus vs. Vaccine-Derived Poliovirus
There are three types of poliovirus (types 1, 2, and 3), and each requires its own specific immunity. Wild poliovirus is the form that circulates naturally and caused the massive outbreaks of the 20th century. It has been eliminated from the U.S. since 1979 and from most of the world, with only a handful of countries still reporting wild cases.
Vaccine-derived poliovirus comes from the weakened virus in the oral polio vaccine. In communities with very low vaccination, this weakened virus can spread from person to person long enough to mutate back toward a form that causes paralysis. These cases are classified differently from wild poliovirus, but they cause the same disease. When vaccine-derived virus is found circulating in a community, it’s called circulating vaccine-derived poliovirus (cVDPV). The 2022 New York case fell into this category.
How the U.S. Monitors for Polio
The primary way the U.S. detects polio is through clinical surveillance. When a patient develops sudden onset of floppy paralysis with decreased or absent reflexes and no more likely diagnosis, testing for poliovirus is triggered. A confirmed case requires both those clinical signs and laboratory detection of the virus.
After the 2022 case, health authorities also turned to wastewater surveillance. Sewage testing can detect poliovirus circulating in a community even when most infected people show no symptoms, which is the majority of polio infections. The CDC does not recommend routine wastewater testing for polio nationwide because overall vaccination rates are high. But targeted testing is recommended for communities with low coverage or significant travel connections to countries with active outbreaks. Wastewater samples are screened with a broad test that picks up all poliovirus types, and any positive results are sent to the CDC for confirmation and genetic sequencing.
One important limitation: finding poliovirus in wastewater cannot tell you how many people are infected. It confirms the virus is present in a community but not the scale of transmission.
What Most Polio Infections Look Like
The vast majority of people infected with poliovirus never develop paralysis. About 70% of infections cause no symptoms at all. A smaller percentage experience mild flu-like illness: fever, fatigue, sore throat, nausea. Paralysis occurs in roughly 1 in 200 infections, depending on the virus type. That means a single paralytic case like the one in 2022 likely represented a larger number of undetected, asymptomatic infections in the surrounding community, which is part of why wastewater testing was deployed.
Current Risk in the U.S.
As of the most recent data, there are zero active polio cases in the United States. The country’s high vaccination rates, use of the inactivated vaccine (which cannot cause vaccine-derived outbreaks), and robust surveillance make a large-scale return of polio extremely unlikely. The risk concentrates in small communities with unusually low vaccination coverage, particularly those with travel ties to regions where poliovirus still circulates. For any individual who has completed the standard childhood vaccine series, the risk of paralytic polio is near zero.