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 one year, killing many of them.
Vaccines turned the tide against the virus. In the past decade, there has been only one case in the United States, linked to international travel.
That could change very quickly if polio vaccination rates fell or the vaccine became less affordable.
Robert F. Kennedy Jr., a longtime vaccine skeptic who may become secretary of Health and Human Services, said the idea that vaccination has nearly eradicated polio is “a mythology.”
And while Mr. Kennedy has said he has no plans to take vaccines away from Americans, he has long claimed they are not as safe and effective as he claims.
As recently as 2023, he said batches of an early version of the virus-tainted polio vaccine caused cancers “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, lawyer and advisor to Mr. Kennedy, represented a client seeking to challenge the approval or distribution of certain polio vaccines on the grounds that they may be unsafe.
These efforts seem unlikely to succeed. And 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 power to discourage vaccination in less direct ways. It could withdraw federal funding for childhood vaccination programs, hasten the end of school mandates in states that are already vaccine-averse, or fuel skepticism about vaccines, exacerbating declining vaccination 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 havoc once again. The virus may have been nearly eradicated in its original form, but a resurgence remains a constant threat.
Any decision by the Trump administration on the polio vaccine is likely to have ripple effects around the world, said Dr. David Heymann, an infectious disease specialist 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 crippled more than 15,000 Americans each year and hundreds of thousands more worldwide. In 1952 alone it 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 horrible polio was,” said Dr. Karen Kowalske, a physician and polio specialist at the University of Texas Southwestern Medical Center in Dallas.
Many who recovered now suffer from “post-polio syndrome”: Some of the original symptoms, including muscle weakness and breathing problems, return.
Dr. Kowalske tends to about 100 post-polio patients who need braces, wheelchairs or other devices to cope with progressive weakness. Some are older adults who were infected before the vaccine was available. Others are middle-aged immigrants from countries where polio has remained 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. Her right leg never recovered and for the rest of her life she walked with a severe limp and was in almost constant pain.
Ms. Paulk is one of the luckiest. Until recently, he did not experience the breathing, swallowing or digestive problems that often plague polio survivors.
He had a “wonderful, wonderful life” with a wife and three daughters, a law degree and extensive foreign travel.
But always, everywhere, she calculates how far the next position is, how long her energy will last, and whether a given activity is worth the pain-killing the next day.
She didn’t participate in the 1963 March on Washington or play sports, as she desperately wanted, or go hiking, skiing and biking with her husband.
If there was a public hearing on the polio vaccine now, “I would go, take off my splint and let them see my leg and ask them, is this what they want for their children?” she said.
Polio cripples far fewer children now. Vaccination has cleared the virus from most of the world, reducing the number of cases by more than 99.9 percent and preventing an estimated 20 million cases of paralysis.
However, the virus has proved a stubborn foe and eradication has been repeated time and time again.
In 2024, 20 countries reported cases of polio, and the virus was detected in sewage in five European countries, decades after it was officially eradicated from the region, and in Australia.
“Any reduction in coverage rates 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 be gone. For years, the goal has been tantalizingly close.
Type 2 was declared defeated in 2015 and Type 3 in 2019. Type 1 is now only in circulation in Afghanistan and Pakistan. In 2021, the two countries combined had just five cases. in 2024 they had 93.
But these figures tell only part of the story. In a surprising twist, an oral vaccine used in some parts of the world has kept the polio virus circulating long after it should have disappeared.
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 administer and prevents transmission of the virus.
But it contains weakened virus, which vaccinated children can lose into the environment through their feces. When there are enough unvaccinated children to become infected, 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 does not protect against Type 2. World health authorities made a deliberate decision to reformulate the vaccine on the grounds that the Type 2 virus that answered nature had disappeared.
This proved premature. More Type 2 virus had been shed by orally vaccinated children in some parts of the world than officials expected. When some unimmunized children, or those who had received the newer oral vaccine, encountered this “vaccine-derived” Type 2 virus, they became infected and paralyzed.
Vaccine-derived poliovirus now paralyzes more children than the naturally occurring virus. For example, Nigeria eliminated all so-called wild-type polio in 2020. But in 2024, the country had 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 children from America protects against all three types of polio. These preparations contain dead virus and therefore cannot cause disease or revert 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 of Mr. Siri, adviser to Mr. Kennedy.
But it’s less important than the near-perfect power of vaccines to prevent paralysis, experts said.
“Yes, yes, it’s true, IPV does not prevent transmission,” said Dr. William Petrie, an infectious disease physician and former chairman of the WHO’s polio research committee. “But, boy, this is the best thing since sliced ​​bread to prevent paralysis.”
It does mean, however, that people who have been vaccinated with IPV can keep the virus circulating, even when they themselves are protected from disease and paralysis.
So here’s a realistic scenario that worries researchers: Someone vaccinated with the 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 most of the population remains vaccinated, this is unlikely to cause an outbreak. But if the virus enters communities with low vaccination rates, it can spread and then revert to an infectious form that can cause paralysis.
This happened in New York in 2022, when polio struck a 20-year-old unvaccinated member of an ultra-Orthodox Jewish community in Rockland County.
The vaccination rate in that county was just over 60 percent, compared to the national average of 93 percent.
The virus that paralyzed the young man circulated for months and was later found in the sewage of several New York counties with vaccination rates hovering around 60%, prompting the state to declare a state of emergency.
Genetically related polioviruses were 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 sewage, suggesting two separate introductions.
If polio were to reappear in the United States, it is unlikely to be as horrific as it was in the decades before vaccination. Many older people still remember that as children they were not allowed to swim in rivers or pools or anywhere the virus might be hiding.
“The reason we weren’t allowed to play in rivers in the 50s is because raw sewage was thrown into the rivers,” said Dr. Heymann.
That’s no longer the case, so “there won’t be a mass broadcast immediately in the US,” he added.
But even if just a few children were paralyzed, “it would be awful.”
