Polio not seen in recent NY wastewater tests: Why it's too early to let down guard

For the first time since a young man in Rockland County was left paralyzed by polio, batches of recent wastewater testing in downstate counties showed no polio. But health officials say it’s way too early to draw conclusions about virus spread, especially with thousands of unvaccinated young children still vulnerable to the virus.

According to the U.S. Centers for Disease Control and Prevention, for a country to be removed from the Global Polio Eradication Initiative’s list of countries with circulating vaccine-derived poliovirus detections, the minimum is 12 months without a detection.

But wastewater testing for polio is relatively new in the United States, so the patterns and thresholds are not yet well understood, said Dr. Eli Rosenberg, deputy director of science for the New York State Department of Health's Office of Public Health. “Polio was eradicated for 40 years. Now we have this technology on board to tell us some information,” Rosenberg said. "We’re still learning.”

Plus, an enterovirus like polio traditionally hits seasonally, with large outbreaks in the summer. “We have to look at the 1950s, when there would be a lull in winter and roar back in summer,” Rosenberg said. Every summer before the development of polio vaccinations, thousands of children would fall ill with paralytic polio, with spikes often coming in August.

“OK, the signal has died down for the winter,” Rosenberg said. “Is polio doing its typical seasonal thing? We don’t know.”

The Rockland resident became ill in July. The state has documented polio in wastewater going back to March, using samples saved from COVID testing protocols.

So far, the Rockland man is the only person found to have had the virus. But health officials on the national, state and local level have been on high alert because polio is stealthy and deadly: Some 99% of people who contract polio never know they had it; others can be paralyzed or die from the virus.

The Rockland resident had never been vaccinated against polio.

The state Department of Health chart for polio detection shows red if the virus was detected in wastewater and blue if polio was not found. Counties where polio had been detected in wastewater included Rockland, Orange, Sullivan, Nassau and parts of New York City.

“If we were in normal times,” Rosenberg said, rather than an era of growing childhood vaccination hesitancy, “this would all be blue.”

Rosenberg called it a “sign of how vulnerable we’ve let our children get.”

Risks for polio spread

The virus could recirculate in warmer months, as it did when it was endemic. But, Rosenberg said, international travel could also reimport the virus here.

The virus strain found in Rockland and other places has been linked to Israel and London.

“To get a fire, you need fuel and a match,” Rosenberg said, “and it’s very similar with the polio virus.”

The match could be another case brought to the region via travel or latent virus already here resurfacing when the weather warms.

The fuel, Rosenberg said, is vaccination resistance that lingers in places like Rockland and Orange counties, which had among the lowest rates of polio vaccination in the state among children ages 2 and under.

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Vaccine hesitancy existed before COVID. A measles outbreak sickened 312 in Rockland almost four years ago. But resistance to vaccinations grew with skepticism over vaccinations for COVID-19.

A recent Kaiser Family Foundation survey showed an increase in the number of adults, including parents, who oppose mandatory childhood vaccinations for school attendance.

While 71% of adults still support mandating childhood vaccinations for healthy children, that’s down from 83% in 2019. Opposition among parents to requiring childhood vaccines now stands at 35%, up from 23% in 2019.

“We know there are more than 21,753 children in Rockland and Orange counties who are not up-to-date with their polio vaccinations,” said Samantha Fuld, spokesperson for the state Department of Health.

That is despite concerted efforts by the state, the U.S. Centers for Disease Control and Prevention and county health departments.

Rockland County Executive Ed Day said that vaccination efforts in that county have yielded results. “Since July 21, 12,603 polio vaccines have been administered to Rockland residents,” Day said, with 77% administered to children ages 4 and under and 16% to ages 5 to 18.

Even with stepped-up efforts, Rosenberg said, “We haven’t moved the needle enough in vaccination.”

Childhood vaccination compliance in New York is mandatory for school attendance, and as of 2019, only documented medical exemptions are accepted. The state this month sent every school, public, private and parochial, a letter reminding them that they can be fined up to $2,000 per student, per day, if students are allowed to attend without vaccination documentation. The state also plans 200 audits this year to ensure school vaccination records are up to snuff.

“We have, as a county, seen outbreaks of vaccine-preventable diseases and the unfortunate low vaccination rates in our county has undoubtedly contributed to the polio case,” Rockland County Health Commissioner Dr. Patricia Schnabel-Ruppert said. “It is our obligation to protect all our residents from these debilitating and potentially fatal diseases. The law requiring childhood vaccinations has been in place for many years for this very reason.”

What wastewater can't show

Because oral-fecal transmission is common with polio, wastewater testing was used decades ago to determine if a water source was a vector for polio.

But in the U.S. and many countries with modern water supply and sewer systems, wastewater doesn’t pose a threat of disease transmission anymore, so wastewater testing for polio usually isn't done.

Wastewater testing for polio is somewhat binary: it can detect presence but not gauge the level of virus present in the community. That differs from wastewater testing for COVID, for example, which can show if the virus is increasing or decreasing in a community over time.

The CDC in September 2020 established the National Wastewater Surveillance System to help communities track COVID rates by gauging virus shedding. New York and other places relied on wastewater data to measure COVID levels as home testing kits became more prevalent and test results were often unknown.

When the Rockland polio case was detected, the CDC had months of previous wastewater samples from COVID tracking to figure out where polio exposure existed and for how long.

"The National Wastewater Surveillance System, originally developed for SARS-CoV-2 monitoring, has provided an opportunity to track the spread of the poliovirus outbreak in New York," said Dr. Janell Routh, Acute Flaccid Myelitis and Domestic Polio team lead in CDC’s Division of Viral Diseases. "Fortunately, there is still only one case of paralysis, but wastewater detections have confirmed ongoing transmission in the area."

Testing then started in several counties throughout New York State. On Nov. 30, the CDC announced it would start testing wastewater for polio in Michigan and parts of Pennsylvania, places with vaccination rates that leave the population at risk.

"Using wastewater testing for poliovirus, combined with clinical surveillance for polio, have proven to be good tools to help direct response efforts, including focused vaccination activities, to areas found to be most at risk," the CDC's Routh said.

Rosenberg urged caution in extrapolating too much from recent wastewater results, citing the cyclical nature of polio, the porous vaccination rate in the region and the relatively new use of wastewater testing in this way.

“This is an unsettled,” Rosenberg said. “Proving a negative is hard.”

Nancy Cutler writes about People & Policy. Follow her on Twitter at @nancyrockland. 

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