Most American parents hardly think about polio beyond the time their child is immunized against the disease. But there was a time in this country when polio paralyzed 20,000 people in a year, killing many.
Vaccines have turned the tide against the virus. There has been only one case in the United States in the past decade, involving international travel.
This could change very quickly if polio vaccination rates decline or the vaccine becomes less accessible.
Robert F. Kennedy Jr., a longtime vaccine skeptic who could become secretary of Health and Human Services, said the idea that vaccination has nearly eradicated polio is “a myth.”
And while Mr. Kennedy has said he has no intention of taking vaccines away from Americans, he has long argued that they are not as safe and effective as claimed.
As recently as 2023, he claimed that batches of an early version of the polio vaccine, contaminated with a virus, caused tumors “that killed many, many, many, many, many more people than polio ever did.” The contamination was real, but research never demonstrated a link to cancer.
Aaron Siri, an attorney and counsel to Mr. Kennedy, represented a client seeking to challenge the approval or distribution of some polio vaccines on the grounds that they may be unsafe.
These efforts seem unlikely to succeed. And there is broad support for vaccination among prominent Republicans, including President-elect Donald J. Trump and Senator Mitch McConnell, who had polio as a child.
But the secretary of Health and Human Services has the authority to discourage vaccination in less direct ways. He or she could withdraw federal funding for childhood vaccination programs, hasten the end of school graduation in already vaccine-unfriendly states or fuel doubts about vaccinations, exacerbating declining immunization rates.
If polio vaccination rates decline, scientists say, the virus could creep into pockets of the country where significant numbers of people are unvaccinated, once again wreaking havoc. The virus may have been nearly eradicated in its original form, but its reemergence remains a constant threat.
Any decisions the Trump administration makes about the polio vaccine will likely have repercussions around the world, said Dr. David Heymann, an infectious disease physician at the London School of Hygiene and Tropical Medicine and former polio eradication leader at the World Organization of Healthcare.
“If the United States takes away the license, many other countries will do the same thing,” he said. A resurgence of polio when it is so close to eradication “would be very, very, very, very sad.”
Before 1955, when the vaccine was introduced, polio disabled more than 15,000 Americans each year and hundreds of thousands more around the world. In 1952 alone he killed 3,000 Americans after paralysis left them unable to breathe.
Many of those who survived are still living with the consequences.
“People really underestimate how terrible polio was,” said Dr. Karen Kowalske, a physician and polio specialist at the University of Texas Southwestern Medical Center in Dallas.
Many of those who have recovered now suffer from “post-polio syndrome”: some of the original symptoms, including muscle weakness and breathing problems, return.
Dr. Kowalske cares for about 100 post-polio patients who require braces, wheelchairs or other devices to deal with progressive weakness. Some are elderly people who became infected before the vaccine was available; others are middle-aged immigrants from countries where polio has been a problem much longer than in the United States.
For some survivors, the idea of polio returning is unfathomable.
Carol Paulk contracted the disease in 1943, when she was just 3 years old. His right leg never recovered, and for the rest of his life he walked with a noticeable limp and was in almost constant pain.
Mrs. Paulk is among the luckier ones. Until recently he did not suffer from the breathing, swallowing or digestion problems that often plague polio survivors.
She had “a wonderful, wonderful life” with a husband and three daughters, a law degree and extensive travel abroad.
But always, everywhere, he calculates how far away the next place is, how long his energy will last, and whether a certain activity is worth the next day’s debilitating pain.
She did not participate in the 1963 March on Washington or play sports, as she desperately wanted, nor did she hike, ski, or bike with her husband.
If there was a public hearing on the polio vaccine now, “I would go, take off my brace, show them my leg and ask them, is this what they want for their children?” he said.
Today, polio disables many fewer children. Vaccination has eliminated the virus from most of the planet, reducing the number of cases by more than 99.9% and preventing an estimated 20 million cases of paralysis.
However, the virus has proven to be a stubborn enemy and its eradication has been thwarted time and again.
As of 2024, 20 countries have reported cases of polio, and the virus has been detected in wastewater in five European countries, decades after its official elimination from the region, and in Australia.
“Any reduction in coverage rates increases the risk of polio everywhere,” said Oliver Rosenbauer, spokesman for the World Health Organization’s polio eradication program.
There are three types of poliovirus, and eradication requires the disappearance of all three. For years, the goal has been incredibly close.
Type 2 was declared missing in 2015 and type 3 in 2019. Type 1 now circulates only in Afghanistan and Pakistan. In 2021, the two countries together have had just five cases; in 2024 they had 93.
But these figures only tell part of the story. In a surprising twist, an oral vaccine used in some parts of the world has kept the poliovirus circulating long after it should have died out.
In most low- and middle-income countries, health officials still rely on an oral vaccine administered as two drops on the tongue. It is cheap and easy to administer and prevents transmission of the virus.
But it contains a weakened virus, which vaccinated children can spread into the environment through feces. When there are enough unvaccinated children to infect, the pathogen slowly spreads, regaining its virulence and eventually causing paralysis.
The problem is this: Since 2016, the oral vaccine used for routine immunization has not protected against type 2 virus. Global health authorities deliberately decided to reformulate the vaccine on the basis that the natural type 2 virus had disappeared.
This proved premature. In some parts of the world, orally vaccinated children shed more type 2 virus than officials expected. When some unimmunized children, or those given the new oral vaccine, encountered this “vaccine-derived” type 2 virus, they became infected and paralyzed.
Vaccine-derived poliovirus now paralyzes more children than the natural virus does. For example, Nigeria eliminated all so-called wild-type polio in 2020. But in 2024, the country recorded 93 cases of the type 2 vaccine-derived virus, more than a third of the global total.
None of this is a problem for Americans, as long as they are vaccinated.
The inactivated polio vaccine (IPV) used for routine immunization of American children protects against all three types of polio. These formulations contain dead viruses and therefore cannot cause disease or return to a dangerous form.
But like some other vaccines for infectious diseases, they do not completely prevent infection or transmission of the virus. This aspect is among the criticisms leveled at Siri, Kennedy’s advisor.
However, it is less important than the vaccines’ near-perfect power to prevent paralysis, experts said.
“Yes, yes, that’s right, IPV does not prevent transmission,” said Dr. William Petri, an infectious disease physician and former chair of the WHO Polio Research Committee. “But, boy, this is the best thing since sliced bread to prevent paralysis.”
This means, however, that people vaccinated against IPV can keep the virus circulating, even when they themselves are protected against disease and paralysis.
So here’s a realistic scenario that worries researchers: Someone who was vaccinated with the oral polio vaccine in another country could bring the virus to the United States, and then spread it, in its weakened form. This has already happened in other countries.
As long as the majority of the population remains vaccinated, an epidemic is unlikely. But if the virus makes its way into communities with low vaccination rates, it could spread and then revert to a virulent form that can cause paralysis.
That’s what happened in New York in 2022, when polio struck an unvaccinated 20-year-old member of an ultra-Orthodox Jewish community in Rockland County.
The vaccination rate in that county was just over 60%, compared to the national average of 93%.
The virus that paralyzed the young man had been circulating for months and was later detected in wastewater in several New York counties with vaccination rates hovering around 60%, prompting the state to declare an emergency.
Genetically related polioviruses have been detected in wastewater samples in Britain, Israel and Canada, suggesting widespread transmission. Authorities later found two separate vaccine-derived type 2 polioviruses in New York wastewater, suggesting two separate importations.
If polio were to reemerge in the United States, it is unlikely to be as bad as in pre-vaccine decades. Many older people still remember that as children they were not allowed to swim in rivers or pools, or anywhere the virus could lurk.
“The reason we weren’t allowed to play in the rivers in the 1950s is because raw sewage was dumped into the rivers,” Dr. Heymann said.
That’s no longer the case, so “there wouldn’t immediately be massive transmission in the United States,” he added.
But even if only a few children were paralyzed, “it would be terrible.”