With growing concern about the circulation of vaccine-derived polioviruses in the United States, the Centers for Disease Control and Prevention said Wednesday that it would work with select communities across the country to conduct wastewater surveillance for the viruses.
The launch of the initiative follows the discovery over the summer of vaccine-derived polioviruses circulating in the sewage of a number of counties in and around New York City. That discovery was made after an unvaccinated man in his 20s was partially paralyzed by polioviruses in July. Since then at least 82 genetically linked viruses have been recovered in sewage samples collected from five counties in and around New York.
The CDC said the work will start in two communities: Oakland County, Mich., and an as-yet-unnamed county in the Philadelphia area. The surveillance may later extend to other parts of the country where polio vaccination rates are low or to locations that have ties to the communities in New York state where polioviruses have been found in wastewater.
“Wastewater testing can be an important tool to help us understand if poliovirus may be circulating in communities in certain circumstances,” José Romero, director of CDC’s National Center for Immunization and Respiratory Diseases, said in a statement.
Some lower-income countries have long used wastewater surveillance to look for the presence of polioviruses. But the Global Polio Eradication Initiative, the partnership that runs the effort to rid the world of polio, only recommends wastewater surveillance for countries like the United States — countries with good sanitation systems and high vaccination rates — when there is an outbreak of polio.
Janell Routh, CDC’s team lead for domestic polio, said the agency has approached some locales to see if they would be willing to conduct wastewater surveillance. In other cases, public health officials have approached the CDC to propose conducting this surveillance, noting they could build it into existing Covid-19 wastewater surveillance.
But looking for polioviruses isn’t as simple as looking for SARS-CoV-2, the virus that causes Covid. That’s because finding viruses triggers the need to make a number of decisions. Risk analyses have to be conducted. Vaccination drives may be needed, if local rates are low. Polio containment protocols that are designed to ensure that viruses in stored diagnostic samples don’t inadvertently reseed polio into the world after eradication will also kick in, requiring hospitals in areas where polioviruses are found in sewage to take precautions with the storage and destruction of stool and respiratory samples, Routh explained.
“Jurisdictions thought: We have this in place. Why not move forward? And it’s been good to have the conversations about ‘Hey, let’s take a step back and think through all of the implications,’” she said.
Romero said careful planning needs to be done before a community undertakes this type of surveillance.
“Finding a poliovirus in a community may not be significant at that moment,” Romero told STAT. “Somebody travels from a region of the world where they use oral polio vaccine, defecates, and it’s in the sewer system — that in and of itself may not be something to be alarmed about. But the jurisdiction needs to be poised to react if you do find something. So all the pieces need to be in place before you go forward on this testing.”
Polio was a global scourge before the development and deployment of polio vaccines in the 1950s and 1960s. The infection is silent in most children, but a small percentage will develop paralysis, often in the limbs. It is not reversible. Sometimes the muscles of the chest are affected, leaving victims unable to breathe on their own.
In 1988, buoyed by the success of the smallpox eradication campaign, the World Health Organization, the CDC, UNICEF (the U.N. Children’s Fund), and the service club Rotary International launched a campaign to try to rid the world of polio. Later the Bill and Melinda Gates Foundation and Gavi, the Vaccine Alliance, joined the effort.
In the years since, two of three types of poliovirus have been snuffed out, but type 1 polio remains, circulating in very low numbers in Pakistan and Afghanistan. Last year polioviruses from Pakistan spread to East Africa, which is currently trying to stop spread there.
So far this year 30 children have been paralyzed by wild polioviruses, as they are called. But in addition to the wild viruses, vaccine-derived viruses circulate — and they are found more broadly. These viruses come from oral polio vaccine, which is used in a number of countries. (The U.S. uses only injectable vaccine, which contains killed viruses.) Several dozen countries have reported finding vaccine-derived viruses this year, and over 500 children have been paralyzed by these viruses.
The vaccine viruses can spread from child to child in places where hygiene is poor and clean water is not available. That sometimes helps the eradication effort; vaccinators don’t need to reach every child. But if the weakened viruses in the oral vaccine circulate for long enough, they can acquire mutations that restore their virulence, rendering them capable of paralyzing an unvaccinated person who ingests them. That is what happened in the New York case.
Kim Thompson, a polio expert and president of the nonprofit Kid Risk, said conducting wastewater surveillance will make sense for some communities, but not for all.
“With the busy holiday travel season here and ongoing detections of polioviruses suggesting continuing transmission in New York, it makes sense for states with known connections to the transmission areas to consider their own wastewater sampling, particularly if their communities are similarly under-vaccinated for polio,” she said in an email.
“For most areas with high polio immunization coverage, the value of testing information will not likely exceed its costs, but higher risk areas may find benefits that lead them to prioritize polio testing.”
Thompson noted, though, that public health authorities in places that conduct the surveillance will need to figure out in advance how to communicate about positive findings, if they arise. Some might be false positives or one-off detections while others may need to be acted on, she said.
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