How Many Cases of Polio Are There in the US?

The United States currently has zero active cases of polio. The last confirmed case of paralytic poliomyelitis in the country occurred in June 2022, when an unvaccinated young man in Rockland County, New York, developed limb weakness caused by a vaccine-derived poliovirus. That single case triggered a massive public health response and revealed something unsettling: the virus had been silently spreading in parts of New York for weeks before anyone noticed.

The 2022 Case and What It Revealed

In July 2022, the New York State Department of Health notified the CDC that poliovirus type 2 had been detected in stool specimens from a 20-year-old unvaccinated man living in Rockland County, New York. He had initially experienced fever, neck stiffness, gastrointestinal symptoms, and limb weakness before being hospitalized with acute flaccid weakness. Testing confirmed the virus was a vaccine-derived poliovirus type 2, meaning it originated from the live oral polio vaccine used in other countries, not from wild poliovirus circulating in nature.¹

This was the first case of paralytic polio in the United States since 2013 and the first documented instance of community transmission of poliovirus in the country since 2005.² The patient, described in one report as a Hungarian traveler, had not been vaccinated against polio.³ He survived, but the virus left lasting damage.

What made the case more alarming than a single unlucky infection was the wastewater evidence. Related polioviruses were found in sewage samples from Rockland County as early as 25 days before the patient’s symptoms started and continued to appear up to 41 days after.¹ Since the vast majority of polio infections cause no paralysis and often no symptoms at all, the single paralytic case almost certainly represented a much larger pool of silent infections spreading through the community.

Silent Spread in the Sewage

After the Rockland County case was identified, seven U.S. jurisdictions, spanning five states and two cities, began testing wastewater for poliovirus. In New York state alone (outside New York City), 86 wastewater samples from seven sewersheds across four counties tested positive for poliovirus type 2 that was genetically linked to the Rockland County patient’s virus. In New York City, six additional positive samples were found between June and October 2022, also linked to the outbreak.²

Researchers also identified a second, genetically distinct vaccine-derived poliovirus type 2 in a New York City sample collected in July 2022, meaning there were actually two separate importation events into the country, not just one.⁴ That second virus did not produce any known paralytic case, but its very presence underscored how easily poliovirus can enter the country undetected. The other participating jurisdictions, including Connecticut, New Jersey, Michigan, and Illinois, found no poliovirus in their wastewater.

The wastewater findings were crucial because they changed the picture from one paralyzed person to evidence of ongoing community transmission across multiple counties. If only one in roughly a hundred to a few hundred polio infections results in paralysis (the well-known ratio for poliovirus), even a single paralytic case implies hundreds of undetected infections.

Why Vaccine-Derived Poliovirus, Not Wild Poliovirus

People sometimes assume a polio case means the wild virus somehow crossed an ocean. The 2022 New York case did not involve wild poliovirus at all. The virus was vaccine-derived, which means it originally came from the live oral polio vaccine (OPV) still used in many countries. OPV contains weakened poliovirus that replicates in the gut, triggering a strong immune response. In rare circumstances, though, that weakened virus can mutate as it passes from person to person in an under-vaccinated community, eventually regaining the ability to cause paralysis.

The United States stopped using OPV for routine immunization in 2000, switching entirely to the inactivated poliovirus vaccine (IPV), which is given by injection. That switch happened because the only cases of paralytic polio occurring in the U.S. by the late 1990s were caused by the oral vaccine itself. Starting in 1999, the Advisory Committee on Immunization Practices, the American Academy of Pediatrics, and the American Academy of Family Physicians recommended IPV for the first two doses, phasing out routine OPV use.⁵ The decision eliminated the small but real risk of vaccine-associated paralysis within the U.S., but it introduced a different vulnerability, one that played out two decades later in Rockland County.

The IPV Trade-Off

IPV is excellent at preventing paralysis. A fully vaccinated person who encounters poliovirus is extremely unlikely to develop the disease. But IPV does not do a great job of stopping the virus from replicating in the gut and being shed in stool. A systematic review found that people vaccinated with OPV were far less likely to shed poliovirus after being exposed compared to unvaccinated people, while IPV provided no meaningful protection against fecal shedding at all.⁶ In other words, IPV-vaccinated people can still carry and pass the virus through their stool without ever knowing it.

This distinction matters. Populations vaccinated entirely with IPV exhibit high levels of asymptomatic fecal shedding, which contributes to person-to-person spread.⁷ There is a nuance, though: IPV can boost intestinal mucosal immunity in people who were previously vaccinated with OPV, producing even stronger mucosal protection than an additional dose of OPV would.⁸ That benefit applies mainly to older adults who received OPV as children, not to young Americans who have only ever received IPV. The practical result is that while no vaccinated American is likely to become paralyzed, the virus could theoretically circulate quietly through an IPV-vaccinated population, posing a real danger only to the unvaccinated people within it.

National Vaccination Rates and Local Gaps

At the national level, polio vaccination rates in the U.S. look reassuring. Coverage for three or more doses of poliovirus vaccine among children by age 24 months has been consistently at or above 90% for over a decade, with the most recent data showing about 92% coverage.⁹ That figure looks good in a headline but hides significant variation at the local level.

Rockland County, where the 2022 case occurred, is historically a county with low vaccination coverage.² Some communities within the county have polio vaccination rates far below the national average. Clusters of unvaccinated or under-vaccinated children create pockets of susceptibility that could sustain local outbreaks and produce paralytic cases.¹⁰ These pockets are often geographically concentrated in communities with religious or philosophical objections to vaccination, making them vulnerable even when the surrounding area is well-protected.

This pattern, high national averages masking dangerously low local rates, is exactly how a disease that has been absent for decades can suddenly reappear. A vaccine-derived poliovirus entering a community with 60% coverage behaves very differently than one entering a community with 95% coverage. The 2022 New York outbreak was not a fluke; it was a predictable consequence of localized under-vaccination meeting an imported virus.

How Poliovirus Keeps Getting Into the Country

The virus that paralyzed the Rockland County patient did not originate in the United States. Vaccine-derived polioviruses circulate in parts of Africa, the Middle East, and Asia where OPV is still used and vaccination coverage is patchy. International travel is the bridge. Someone infected abroad, or recently vaccinated with OPV abroad, can carry the virus into the U.S. in their gut and shed it in the sewage system without ever feeling sick. The 2022 investigation showed two separate importation events occurred within a short window, which is a strong indication that these introductions are not vanishingly rare.⁴

Wild poliovirus itself remains endemic in only two countries, Afghanistan and Pakistan. But vaccine-derived polioviruses have been detected in dozens of countries across multiple continents in recent years. As long as any form of poliovirus circulates anywhere in the world and international travel continues, the risk of importation into the U.S. is not zero. What keeps that importation from becoming an outbreak is vaccination coverage, and as Rockland County demonstrated, the relevant coverage is local, not national.

Poliovirus vs. Other Causes of Paralysis

One reason the 2022 case drew such attention is that polio-like paralysis had already been showing up in American children without any poliovirus involvement. Starting in 2014, clusters of acute flaccid myelitis, a condition that looks clinically similar to paralytic polio, began appearing in the United States, mostly in children. The suspected cause was a different virus entirely: enterovirus D68. Surges of enterovirus D68 in 2014 and 2016 coincided in timing and geography with spikes in acute flaccid myelitis cases, though proving a direct causal link proved frustratingly difficult because the virus was rarely found in spinal fluid or affected tissue.¹¹

When the Rockland County patient presented with limb weakness, clinicians initially considered acute flaccid myelitis as a possible diagnosis.¹² It was only the stool testing that confirmed poliovirus. This overlap matters because doctors working in the U.S. have not seen paralytic polio in their careers and might not immediately suspect it. The 2022 case served as a wake-up call that poliovirus needs to remain on the list of possibilities when a patient presents with sudden paralysis, particularly if they are unvaccinated.

The Cost of a Single Case

Responding to even one polio case turned out to be enormously expensive. Following the Rockland County confirmation, the New York State Department of Health, local health departments, and the CDC launched an investigation and response effort. Just two components of that response, provider outreach and reviewing immunization records at childcare and pre-kindergarten facilities in Rockland County, cost an estimated $138,514 and consumed over 2,500 hours of labor.¹³ That figure covers only a fraction of the total response, which also included wastewater surveillance across multiple states, emergency vaccination campaigns, laboratory testing, and epidemiological investigation. The total bill was orders of magnitude higher.

These costs are, by definition, avoidable for a vaccine-preventable disease. Every dollar spent chasing a polio outbreak is a dollar that routine vaccination would have made unnecessary. From a public health economics standpoint, the 2022 response made a clear case that maintaining high, uniform vaccination coverage is dramatically cheaper than responding to the consequences of letting it slip.

Polio Survivors Still Living in the U.S.

While new polio cases in the U.S. are extraordinarily rare, the legacy of the disease is very much alive. Millions of Americans contracted polio during the epidemics of the 1940s and 1950s, and a substantial number of survivors still live with its effects. Globally, about 20 million polio survivors exist, and a sizable proportion are Americans now in their 60s, 70s, and 80s.

Many of these survivors face a condition called post-polio syndrome, a group of symptoms that emerge 15 to 30 years after the original infection. Estimates of how many survivors develop it vary widely, ranging from about 15% to 80%, depending on the study and the criteria used.¹⁴ Symptoms typically include new muscle weakness, fatigue, muscle and joint pain, difficulty swallowing, and breathing trouble. Some survivors also report cold intolerance, sleep problems, and cardiovascular issues.

As these survivors age, their challenges compound. Polio survivors frequently experience accelerated functional decline, and falls are a serious hazard. Roughly two-thirds of polio survivors report major falls, and about a third of those result in fractures, often at the hip or thigh bone.¹⁵ Osteoporosis, arthritis, and cardiopulmonary dysfunction are common co-occurring conditions. For this population, polio is not a historical curiosity but an ongoing medical reality that shapes their daily lives. The health system still bears a significant burden from a disease that last caused widespread epidemics in the U.S. over half a century ago.

What Wastewater Surveillance Changed

Before 2022, the U.S. did not routinely test wastewater for poliovirus. The Rockland County case, along with the COVID-era expansion of sewage monitoring, changed that. The fact that poliovirus was detectable in wastewater weeks before the paralytic case was identified demonstrated that sewage surveillance could serve as an early-warning system for a virus that mostly spreads silently.

The 2022–2023 wastewater testing effort covered seven jurisdictions, and while poliovirus was found only in New York, the effort proved the concept. The positive samples from multiple counties and the identification of two separate importation events would not have been possible through clinical surveillance alone, since only one person developed symptoms severe enough to seek medical care and get tested.² For a virus where the overwhelming majority of infections are invisible, wastewater may be the only realistic way to know whether poliovirus is circulating in a community before someone becomes paralyzed.

Whether the U.S. will maintain and expand routine poliovirus wastewater surveillance in the long term remains an open question. The infrastructure built for SARS-CoV-2 monitoring gave public health agencies a head start, but sustained funding and political will are different things. If the surveillance lapses, the next importation event could again go unnoticed until it produces a paralytic case, by which point the virus may have been spreading for weeks.

1
PubMed Central. Public Health Response to a Case of Paralytic Poliomyelitis in an Unvaccinated Person and Detection of Poliovirus in Wastewater – New York, June-August 2022
2
Emerging Infectious Diseases. Wastewater Surveillance for Poliovirus in Selected Jurisdictions, United States, 2022–2023
3
PubMed Central. Polio returns to the USA: An epidemiological alert
4
PubMed Central. Wastewater Surveillance for Poliovirus in Selected Jurisdictions, United States, 2022-2023
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Seminars in Pediatric Infectious Diseases. Polio vaccination schedules in the United States: The rationale for change
6
PLoS Pathogens. Systematic Review of Mucosal Immunity Induced by Oral and Inactivated Poliovirus Vaccines against Virus Shedding following Oral Poliovirus Challenge
7
PubMed Central. Oral live attenuated polio vaccines induce enhanced T-cell responses with broad antigen recognition compared to inactivated polio vaccines
8
PubMed Central. Impact of inactivated poliovirus vaccine on mucosal immunity: implications for the polio eradication endgame
9
Morbidity and Mortality Weekly Report. Vaccination Coverage by Age 24 Months Among Children Born in 2021 and 2022 — National Immunization Survey-Child, United States, 2022–2024
10
PubMed Central. Trends in the risk of U.S. polio outbreaks and poliovirus vaccine availability for response
11
PubMed Central. Enterovirus D68 and acute flaccid myelitis-evaluating the evidence for causality
12
PubMed. Re-Emergence of Poliovirus in the United States: Considerations and Implications
13
PubMed Central. 2022 Polio outbreak, Rockland County, NY: Cost evaluation of strategies to prevent future outbreaks of vaccine-preventable diseases
14
PubMed Central. Postpolio Syndrome: A Review of Lived Experiences of Patients
15
Ewha Medical Journal. Aging with disability in polio survivors: a narrative review