How Long Has Polio Been Circulating in the U.S.?


 The virus has likely been circulating in U.S. cities intermittently for years, experts say.

The fact that poliovirus was detected in New York City wastewater samples as far back as April of this year shouldn’t be surprising, as the virus likely has been circulating for longer and more widely than previously believed, several experts told MedPage Today.

“I think you’re gonna see over the next weeks more and more reports of poliovirus in wastewater elsewhere,” said Vincent Racaniello, PhD, a virologist at Columbia University in New York City.

Poliovirus probably still circulated in the U.S. after 2000, when officials stopped giving the oral polio vaccine, he said. That version protects against paralysis and provides short-term protection against intestinal infection from poliovirus.

The transition to injectable polio vaccine, which is equally as effective against paralysis but not against intestinal infection, meant that the U.S. population was more susceptible to transmitting vaccine-associated poliovirus, he explained.

This circulation is likely occasional and sporadic, he said, but the threat to vulnerable populations is still high.

“Here’s the thing: polio is here in the U.S. It’s not gone,” Racaniello said. “It’s in the wastewater. It could contaminate you, so if you’re not vaccinated, that could be a problem.”

Calls for Nationwide Surveillance

Racaniello said there’s value in learning more about the circulation of the virus, especially for communities with low vaccination rates.

The first step to understanding how long and how broadly poliovirus is circulating, he said, is to start testing wastewater everywhere. The CDC used stored wastewater from April to confirm that the virus had been circulating then, but it is just as possible to conduct nationwide surveillance for poliovirus now, he noted.

In fact, Racaniello said, he has long believed that this kind of surveillance should be done routinely to provide an early detection system for poliovirus.

“Ten years ago, I said to the CDC, you should really be looking in the sewage for poliovirus because of this issue where it could come in from overseas and be in our sewage,” he said. “If someone is unvaccinated, that would be a threat to them, but [the CDC] never did it.”

Davida Smyth, PhD, of Texas A&M University-San Antonio, pointed out that the National Wastewater Surveillance System (NWSS) was established to detect COVID-19 in 2020, so the infrastructure to conduct a wide search for the spread of polio is available.

The primary issue, she said, is that the collaboration that academic researchers have enjoyed with the CDC in surveillance of COVID-19 is so far absent with poliovirus.

“I imagine the CDC is testing those samples for polio, even as we speak, given the nature of what has happened,” Smyth said.

Better coordination with academia and better surveillance, she said, is crucial for finding any potential pockets of poliovirus circulating in other communities around the U.S.

In fact, she said, she is “absolutely convinced” that more polio will be found in the coming weeks.

MedPage Today contacted the CDC to ask whether there are plans to use the NWSS to look for polio around the U.S., but as of press time had not received a response.

Smyth noted that most areas in the country have high rates of polio vaccination, but she is concerned about pockets of rural America where vaccination has dipped in recent years. Most states boast polio vaccination rates over 90%, but Smyth said in some regions, the percentages may be as low as the mid-30s.

“[In] the vast majority of the United States, the vaccination rates are quite high, but the COVID pandemic has led to a decrease in vaccination rates,” Smyth told MedPage Today. “The rates are going down. They’re dipping below 90%, which is shocking, frankly.”

Smyth said the decline is largely due to a lack of opportunity or access to healthcare in some areas, but vaccine hesitancy around the COVID-19 vaccine might be affecting polio vaccinations as well.

“There’s a variety of reasons why people don’t get vaccinated,” she said. “The problem is children are very vulnerable. So if you have a population where the vaccination rates drop, those are exactly the kinds of areas where we need to do this surveillance.”

Racaniello echoed the importance of polio vaccination in adults as well. If patients don’t have a record of their shot, “just vaccinate them,” he said, “because there’s no downside to getting vaccinated again.”

Re-evaluating the Polio Endgame

The recent case of paralytic polio infection and concerns over the wider circulation of poliovirus have also altered some of the thinking around the goal of polio eradication.

In fact, William Schaffner, MD, of Vanderbilt University Medical Center in Nashville, highlighted the unique difficulty of preventing the spread of poliovirus.

“As you can imagine, we’ve gotten into polio endgame,” he told MedPage Today. “I think the notion has now been modified. Eradication isn’t going to be as neat and clean and quick as we once thought. Once we get rid of all paralytic disease, we will have to keep vaccinating for a long time, because there will still be circulating vaccine-associated viruses — some of which will mutate back.”

Schaffner compared the final push to eradicate polio with the successful eradication of smallpox. When the last case of smallpox ended, he explained, public health officials were able to end smallpox vaccination campaigns. For polio, however, he said, it will likely not be that simple, and it will be necessary “to keep vaccinating for quite a long time.”

He said that as public health officials in the U.S. and globally continue to grapple with the nuances of eradicating poliovirus, healthcare providers and their patients will have to come to terms with the simple fact that polio is a real health concern.

“[It’s] the reverse of the old saying, ‘it’s gone, but not forgotten,'” Schaffner said. “Polio is forgotten, but it’s not gone.”

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