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Most American parents hardly think about polio after the moment their child is immunized against the disease. But there was a time in this country when polio paralyzed 20,000 people a year, killing many of them.
Vaccines have turned the tide against viruses. In the past decade, only one case has been reported in the United States, linked to international travel.
That could change very quickly if polio vaccination rates drop or if the vaccine becomes less available.
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 “mythology.”
And while Mr. Kennedy said he has no plans to take vaccines away from Americans, he has long argued they are not as safe and effective as claimed.
As recently as 2023, he said batches of an early version of the polio vaccine, contaminated with the virus, caused a cancer “that killed many, many, many, many, many more people than polio ever did.” The contamination was real, but research never proved a link to cancer.
Aaron Siri, a lawyer and adviser to Mr. Kennedy, represented a client who wants to challenge the approval or distribution of some polio vaccines on the grounds that they may be unsafe.
These efforts seem unlikely to succeed. There is widespread 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, accelerate the end of school mandates in already vaccine-averse states, or foster skepticism about vaccines, exacerbating declining immunization rates.
If polio vaccination rates fall, scientists say, the virus could slip into pockets of the country where significant numbers of people are unvaccinated, wreaking further havoc. The virus may be nearly eradicated in its original form, but resurgence remains a constant threat.
Any decision the Trump administration makes regarding the polio vaccine is likely to affect the entire world, said Dr. David Heymann, an infectious disease doctor at the London School of Hygiene and Tropical Medicine and former head of polio eradication at the World Health Organization.
“If the US takes away the license, then 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 worldwide. In 1952 alone, it killed 3,000 Americans after they lost their ability to breathe due to paralysis.
Many of those who survived are still living with the consequences.
“People really underestimate how horrible polio was,” said Dr. Karen Kowalske, a physician and polio specialist at the University of Texas Southwestern Medical Center in Dallas.
Many who have recovered now suffer from “post-polio syndrome”: some of the original symptoms, including muscle weakness and respiratory problems, return.
dr. Kowalske cares for about 100 post-polio patients who need braces, wheelchairs or other devices to cope with progressive weakness. Some are elderly people who became infected before the vaccine became 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 fell ill in 1943, when she was only 3 years old. Her right leg never recovered, and for the rest of her life she walked with a severe limp and was in almost constant pain.
Mrs. Paulk is among the luckier ones. Until recently, she did not suffer from the breathing, swallowing or digestion problems that often plague polio survivors.
She had a “wonderful, wonderful life” with her husband and three daughters, a law degree and extensive travels abroad.
But always, everywhere, she calculates how far the next seat is, how long her energy will last, and whether a particular activity is worth the debilitating pain of the next day.
She did not participate in the March on Washington in 1963, nor did she play sports, as she desperately wanted, nor did she go hiking, skiing and cycling with her husband.
If there was a public debate about the polio vaccine now, “I would go, take off my brace, let them see my leg and ask them if they want that for their children?” she said.
Polio now causes far fewer disabled children. Vaccination has wiped out the virus from much of the planet, reducing cases by more than 99.9 percent and preventing an estimated 20 million cases of paralysis.
Still, the virus proved to be a stubborn foe, and eradication slowed time and time again.
In 2024, 20 countries reported cases of polio, and the virus was detected in wastewater in five European countries, decades after official elimination from the region, and in Australia.
“Any reduction in coverage increases the risk of polio anywhere,” said Oliver Rosenbauer, spokesman for the World Health Organization’s polio eradication program.
There are three types of poliovirus, and eradication requires all three to disappear. For years, the goal was tantalizingly close.
Type 2 was declared defeated in 2015 and Type 3 in 2019. Type 1 is now circulating only in Afghanistan and Pakistan. In 2021, the two countries combined had only five cases; In 2024, they had 93.
But those numbers tell only part of the story. In a surprising twist, an oral vaccine used in some parts of the world has kept poliovirus in circulation long after it should have died out.
In most low- and middle-income countries, health officials still rely on an oral vaccine given as two drops on the tongue. It is cheap and easy to use and prevents the transmission of viruses.
But it contains a weakened virus, which vaccinated children can spread into the environment with their feces. When there are enough unvaccinated children to infect, the pathogen slowly spreads, regaining its virulence and eventually causing paralysis.
The problem is this: As of 2016, the oral vaccine used for routine immunization did not protect against the type 2 virus. Global health authorities made a deliberate decision to reformulate the vaccine based on the fact that the naturally occurring type 2 virus had disappeared.
That turned out to be premature. Orally vaccinated children in some parts of the world shed more type 2 virus than officials expected. When some unvaccinated children, or those who received the newer oral vaccine, encountered this type 2 “vaccine” virus, they became infected and paralyzed.
Vaccine-derived poliovirus now paralyzes more children than the natural virus. For example, Nigeria eliminated all so-called wild types of polio in 2020. But in 2024, 93 cases of vaccine-derived virus type 2 were recorded in the country, which is more than one third of the total worldwide.
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 virus and therefore cannot cause disease or revert to a dangerous form.
However, like some other infectious disease vaccines, they do not completely prevent infection or transmission of the virus. This aspect is among the criticisms of Mr. Siri, Mr. Kennedy’s adviser.
Still, that’s less important than the vaccine’s near-perfect power to prevent paralysis, experts say.
“Yes, yes, it’s true, IPV does not prevent transmission,” said Dr. William Petri, infectious disease physician and former chairman of the WHO Polio Research Committee. “But, boy, it’s the best thing since sliced bread in preventing paralysis.”
However, this means that people vaccinated with IPV can keep the virus circulating, even when they themselves are protected from disease and paralysis.
Here’s a realistic scenario that worries researchers: Someone vaccinated with oral polio vaccine in another country could bring the virus into the United States and then shed it, in its weakened form. This has already happened in other countries.
As long as the majority of the population is vaccinated, it is unlikely to cause an outbreak. But if the virus makes its way into communities with low vaccination rates, it can spread and then revert to a virulent form that can cause paralysis.
This happened in New York in 2022, when polio struck a 20-year-old unvaccinated member of the ultra-Orthodox Jewish community in Rockland County.
The vaccination rate in that county was slightly higher than 60 percent, compared to the national average of 93 percent.
The virus that paralyzed the young man circulated for months, and was later discovered in the sewers of several New York counties with a vaccination rate hovering around 60 percent, prompting the state to declare a state of emergency.
Genetically related polioviruses have been detected in sewage samples in Britain, Israel and Canada, suggesting widespread transmission. Authorities later found two different type 2 vaccine-derived polioviruses in New York’s sewage, indicating two separate imports.
If polio were to reappear in the United States, it is unlikely that it would be as dire as it was in the decades before vaccination. Many older adults still remember that as children they were not allowed to swim in rivers or pools, or anywhere the virus might lurk.
“The reason we weren’t allowed to play in the rivers in the 50s was because the sewage was dumped into the rivers,” said Dr. Heymann.
That’s no longer the case, so “there wouldn’t be immediate mass transmission in the US,” he added.
But even if only a few children were left paralyzed, “that would be terrible.”
