New York State reported Thursday that it has detected a case of vaccine-derived polio in an unvaccinated adult in Rockland County, north of New York City, the first such case in the United States since 2013.

The unidentified individual developed paralysis, said Beth Cefalu, Rockland County’s director of strategic communications. Polio paralysis is irreversible.

The area where the case was detected was the epicenter of a large measles outbreak in 2018-2019 that was fueled by low vaccination rates among communities of Hasidic Jews. The outbreak went on for so long that the country almost lost its measles-free status. The memory of that episode is provoking concern that the area might be ripe for additional vaccine-derived polio cases to occur.

“I think it’s concerning because … it can spread,” said Walter Orenstein, a polio expert at Emory University. “If there are unvaccinated communities, it can cause a polio outbreak.”

“The inactivated polio vaccine we have is very effective and very safe and could have prevented this,” he said. “We need to restore our confidence in vaccines.”

The Centers for Disease Control and Prevention said in a statement that while the risk is low for people who are vaccinated, there is risk for those who have not had the recommended three doses of injectable polio vaccine.

“Most of the U.S. population has protection against polio because they were vaccinated during childhood, but in some communities with low vaccine coverage, there are unvaccinated people at risk,” the statement said. “Polio and its neurologic effects cannot be cured, but can be prevented through vaccination.”

The New York State department of health said in a statement that the person was infected with a type 2 vaccine-derived poliovirus, which would have come from oral polio vaccine used in a number of countries, but not the United States. The U.S. stopped using oral polio vaccine in 2000.

Cefalu told STAT the case is still being investigated, but it is believed the individual had not recently traveled outside the country to a place where type 2 vaccine-derived polio viruses are spreading. If that is the case, that would indicate someone else inadvertently imported the virus, suggesting there may be additional undetected transmission. Only a small portion of people infected with polioviruses will go on to be paralyzed.

Kimberly Thompson, a polio expert who is president of the nonprofit organization Kid Risk, said it’s not a surprise to see a vaccine-derived case pop up in this country, noting public health authorities in the United Kingdom recently discovered vaccine-derived polioviruses  in sewage in London, indicating some transmission there. 

“With Covid having disrupted immunization (even in the U.S.) and travel now having resumed and much more type 2 poliovirus transmission happening … it’s been only a matter of time before we’d have some detection of polioviruses in sewage, as happened recently in the U.K, or more tragically, a case,” Thompson told STAT in an email. “There’s just a lot more polio going around than there should be.”

The oral vaccine contains live but weakened polioviruses, which immunized children excrete in their stools. In places where hygiene is poor, these viruses can spread from child to child, immunizing others as they do. But as they spread, the vaccine viruses can regain the power to paralyze. Such cases are called vaccine-derived polio.

The United States uses injectable polio vaccine that contains killed viruses to teach the immune system to recognize and fight off polio. It cannot cause paralysis.

Mary Bassett, New York State’s health commissioner, said people who are vaccinated against polio do not face a risk from the newly discovered case. But children who are not immunized against the virus should receive the vaccine.

“Based on what we know about this case, and polio in general, the Department of Health strongly recommends that unvaccinated individuals get vaccinated or boosted with the FDA-approved IPV polio vaccine as soon as possible,” Bassett said.

Rockland County will host vaccine clinics on Friday and Monday, the department’s statement said.

The United States used to have upwards of 20,000 paralytic polio cases a year in the early and mid-1950s, Orenstein said, recalling that as a 7-year-old in 1955 he was reluctant to be vaccinated when the Salk polio vaccine — the injected form — was released. “My mother said to me: ‘Better you should cry than I should cry,’’’ he said.

With the advent of effective polio vaccines, the disease retreated in much of the developed world. The last recorded case of domestically acquired wild polio was in 1979, though there was an imported case in 1993.

But over the years there have been rare imported cases of vaccine-derived polio, from countries where the oral vaccine is still in use.

Following the flow of money through the health care industry.

Orenstein said detecting where the virus in the New York case came from is critical. That work can be done by comparing the genetic sequence of the individual’s virus with others in a database the polio eradication program maintains.

The world has been trying to eradicate polio for decades, with two of the original three types of polio — types 2 and 3 — having been driven out of existence. But the remaining version, type 1, has defied efforts to end its spread to date.

Wild-type polio cases are at low numbers; the viruses are only endemic at this point in Afghanistan and Pakistan, which have recorded a total of 12 cases this year. But recently it was discovered that viruses from Pakistan had made their way to Malawi and Mozambique, a highly unwelcome development.

Meanwhile, the numbers of vaccine-derived cases have exploded in Africa and some other parts of the world after the failure of an effort in 2016 to take type 2 viruses out of the oral vaccine.

It was felt that given the fact that wild type 2 viruses no longer existed, it was not ethical to use oral vaccine containing type 2 viruses, because of the risk they would regain the power to paralyze.

In a coordinated move called “the switch,” countries around the world were told to stop using trivalent oral vaccine — vaccine that contained all three types of polioviruses — and begin to use a bivalent form that did not include type 2. In the years since, chains of transmission of type 2 vaccine-derived virus have spread to more than 40 countries around the world and the polio eradication program has struggled to contain the spread.

So far this year 167 children in 12 countries have been paralyzed by type 2 vaccine viruses, not including the individual in New York.

The Global Polio Eradication Program, which leads the effort to rid the world of polio, said in a statement that the discovery highlights the importance of countries continuing to be on the lookout for polio, noting “any form of poliovirus anywhere is a threat to children everywhere.”

“It is vital that all countries, in particular those with a high volume of travel and contact with polio-affected countries and areas, strengthen surveillance in order to rapidly detect any new virus importation and to facilitate a rapid response,” the statement said. “Countries, territories, and areas should also maintain uniformly high routine immunization coverage … to protect children from polio and to minimize the consequences of any new virus being introduced.”

The polio eradication program is a partnership involving the World Health Organization, the United Nations Children’s Fund, the service group Rotary International, the Centers for Disease Control and Prevention and the Bill and Melinda Gates Foundation.