Understanding Polio's Emergence in New York

Unlike COVID-19 or the flu, polio is entirely and permanently preventable. In fact, until this year, there had not been one case of polio that originated in this country since 1979. A case in 1993 was brought to these shores by someone who had traveled to a country where the disease was endemic.

As long as you and your children are vaccinated, you have nothing to worry about. But if you are unvaccinated or under-vaccinated, doctors and public health officials urge you to waste no time in getting the polio vaccine, which confers lifelong protection against a potentially disabling disease.

The public health picture

A handful of polio-caused paralysis cases in New York, London and Jerusalem may seem minor compared to the massive global impact of the COVID-19 pandemic. But in public health terms, the recent polio outbreak is anything but minor. That’s because the poliovirus causes paralysis in fewer than 1 in 200 of the people it infects, according to the World Health Organization (WHO). Think of the one case of paralysis in New York’s Rockland County as the tip of a very large iceberg.

Says Dr. Karen Acker, Assistant Professor of Clinical Pediatrics at Weill Cornell Medicine and Assistant Attending at Phyllis and David Komansky Children’s Hospital at NewYork-Presbyterian Hospital, “The poliovirus generally causes nothing more than cold symptoms. In the vast majority of cases, people experience mild symptoms or no symptoms at all.” Then, there’s that one terrible case of paralysis, usually a child.

The history of polio is one marked by tragedy followed by a happy ending: a vaccine capable of blocking its disabling impact, permanently. That’s the ending we thought we had since 1979. Now, after more than 40 years, the disease is on the rise again.

Remembering the polio epidemic

The polio epidemic in the U.S. peaked in the late 1940s and 1950s. The Centers for Disease Control and Prevention (CDC) estimates that the disease disabled roughly 35,000 people a year, mostly children. During the summer, parents were afraid to let their children go outdoors. Playgrounds and swimming pools were considered breading grounds of contagion.

President Franklin Delano Roosevelt contracted polio as an adult. Unable to walk, he lived with his disability, and governed the country, with skill and dignity. Roosevelt’s plight became more widely known after his death in 1945 and served to draw attention to a public health crisis that demanded all the resources the country could muster.

Then, in 1955, Jonas Salk developed a vaccine that sharply curbed the polio epidemic. The end was in sight.

In 1961, Albert Sabin created a second vaccine—an oral formulation administered in a child-friendly sugar cube. Both vaccines confer lifelong immunity to polio, and both are still in widespread use today.

Back to the present

In 1979, there were no remaining cases of polio-related paralysis in the U.S., and the world seemed to be en route to eradicating polio once and for all. That goal is still a ways off, public health experts say.

The vast majority of people in the U.S. have received all the required doses of the Salk or Sabin vaccine. “Polio is actually a showcase for how well vaccines work,” says Dr. Acker.

However, vaccines are only as effective as the campaigns to get people vaccinated. If you or your children are unvaccinated, or if you have not received a complete series of vaccine doses, you are vulnerable to infection by the polio virus—and to that 1 chance in more than 200 that you’ll suffer the worst outcomes of the disease.

The good news is that it’s never too late to decide to get vaccinated.

Unpacking the problem

Let’s return to the two polio vaccines: Salk’s injectable version and Sabin’s oral formulation.

The injectable vaccine uses inactivated (dead) virus to stimulate a powerful, lifelong immune response against polio—especially against its most feared consequences: paralysis and even death. However, the oral vaccine is more effective in curbing transmission.

Still, the oral vaccine has an important downside. As Dr. Acker explains, “The oral formula contains weakened but live virus, which can be shed in the stool. Vaccine-derived polio virus has been found in New York’s waste water—both in the city and surrounding metropolitan area.”

The latest source of infection

We can thank the city’s waste water measurement system for its role in assessing the extent of polio infection and spread, she says. The system has been strengthened during the COVID-19 pandemic to measure the presence of the new coronavirus and other sources of infection, including the poliovirus.

“To be clear, the oral vaccine doesn’t cause infection. But the viral shedding we’ve seen in waste water tells us that people are being exposed to the virus. If it mutates enough, it can infect an unvaccinated person. In fact, it already has.”

Originally, there were three strains of wild poliovirus: types 1, 2 and 3. Types 2 and 3 have been eradicated through global health efforts, but type 1 continues to circulate in Pakistan and Afghanistan. With these two exceptions, polio outbreaks in other parts of the world are caused by the strain contained in the oral polio vaccine, including the case seen in New York this past July, Dr. Acker says. “That vaccine-derived strain doesn’t cause problems if everyone is vaccinated, but if there are enough unvaccinated or under-vaccinated people around, and if the weakened virus from the vaccine circulates in that community long enough, it can revert to a form that can cause paralytic disease.”

The vaccine challenge

The polio virus has an uncanny way of finding unvaccinated individuals, Dr. Acker says. Entire communities of unvaccinated people in Rockland County and other areas in or near New York City are at risk for contracting and spreading the virus.

Again, the majority of us have lifelong immunity from polio, thanks to prior vaccination. Even older adults who received the vaccine as children during the 1950s or 1960s are protected. But the small, unvaccinated minority are at risk.

Persuading individuals and communities to get vaccinated is a major public health priority, Dr. Acker says.

Vaccination guidelines


  • Adults who are unvaccinated against polio, or who are unsure if they have been fully immunized, should receive their first dose at any time—as soon as possible; their first dose at any time—as soon as possible; their second dose 1 to 2 months later; and their third dose 6 to 12 months after the second.
  • Adults who have had 1 or 2 doses in the past should get their remaining 1 or 2 doses, no matter how long it has been since their earlier dose(s).
  • Some health-care workers and travelers to countries where polio remains endemic—even if they have been fully vaccinated in the past—are eligible to receive one lifetime booster dose of the injectable vaccine. The booster is not recommended for any other groups or individuals.


  • All children should receive 4 doses of the polio vaccine: their first dose at 2 months; their second dose at 4 months; their third dose at 6 through 18 months; and their fourth dose at 4 through 6 years of age.
  • Children under 4 months of age are protected by antibodies from their mother.
  • All of Weill Cornell’s primary care sites routinely vaccinate all children for polio via the inactivated, injectable vaccine during their 2-month, 4-month, 6-month and 4-year-old wellness visits.

If you wish to discuss your vaccination status, please schedule a visit with your primary care doctor on Connect or by calling 646-962-8000.

For more information about the polio vaccine, please visit CDC.

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