How delayed vaccination could lead to a resurgence of polio

Most American parents don’t think about polio beyond the moment 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 have turned the tide against the virus. In the last decade, there has been only one case in the United States, linked to international travel.

That could change very quickly if polio vaccination rates drop or the vaccine becomes less accessible.

Robert F. Kennedy Jr., a longtime vaccine skeptic who may become the secretary of health and human services, said the idea that vaccination nearly eradicated polio is “a mythology.”

And while Mr. Kennedy said he did not plan to take vaccines out of the Americans, he has long argued that they are not as safe and effective as claimed.

Until 2023, he said that batches of an early version of the polio vaccine, contaminated with a virus, caused cancers “that killed many, many, many, many, many more people than polio. The contamination it was true, but the research it never bore a link with cancer.

Aaron Siri, lawyer and adviser to Mr. Kennedy, represented a client who seeks to challenge the approval or distribution of certain polio vaccines on the grounds that they may be unsafe.

Those efforts seem unlikely to succeed. And there is general 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 funds for childhood vaccination programsaccelerate the end of the school mandates in the states already contempt for vaccines or fuel doubts about the shots, exacerbating a decrease in immunization rates.

If polio vaccination rates fall, scientists say, the virus could break out into pockets of the country where significant numbers of people are not vaccinated, wreaking havoc once again. The virus may be almost eradicated in its original form, but resurgence remains a constant threat.

Any decision the Trump administration makes on the polio vaccine is likely to reverberate around the globe, said Dr. David Heymann, an infectious disease physician at the London School of Hygiene and Tropical Medicine and former head of eradication of polio in the World Health Organization.

“If the United States takes the license, then many other countries will do the same thing,” he said. Resurrecting 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 a 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 have recovered now suffer “post-polio syndrome”: Some of the original symptoms, including muscle weakness and respiratory 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 became infected before the vaccine was available; others are middle-aged immigrants from countries where polio has been a problem for 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 only 3. Her right leg never recovered, and for the rest of her life she walked with a pronounced limp and was in almost constant pain.

Ms. Paulk is among the luckiest. Until recently, he did not suffer from the breathing, swallowing or digestive 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, it is calculated how far is the next seat, how long his energy will last and if a certain activity is worth debilitating the pain the next day.

She did not 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, and take off my brace, and let them see my leg and ask them, is this what they want for their children?” she said.

Polio disables much less now. Vaccination has cleared the virus from most of the planet, reducing the number of cases by more than 99.9 percent and preventing about 20 million cases of paralysis.

However, the virus has become a stubborn enemy, and eradication has been postponed several times.

In 2024, 20 countries reported cases of poliomyelitis, and the virus was 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, a spokesman for the World Health Organization’s polio eradication program.

There are three types of poliovirus, and eradication requires that all three disappear. For years, the goal has been very close.

Type 2 was declared obsolete in 2015, and type 3 in 2019. Type 1 now circulates only in Afghanistan and Pakistan. In 2021, the two countries together had only 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 poliovirus circulating long after it should have died.

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 the transmission of the virus.

But it contains a weakened virus, which vaccinated children can spread into the environment through their feces. When there are enough unvaccinated children to infect them, the pathogen slowly spreads, regaining its virulence and eventually causing paralysis.

The problem is this: Since 2016, the oral vaccine used for routine immunization does not protect against the Type 2 virus. Global health authorities have made a deliberate decision to reformulate the vaccine on the grounds that the Type 2 virus natural had disappeared.

What you do it became premature. More type 2 virus has been spread by orally vaccinated children in some parts of the world than officials had anticipated. When some unimmunized children, or those given 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 natural virus. For example, Nigeria eliminated all wild-type polio in 2020. But in 2024, the country saw 93 cases of the virus derived from the Type 2 vaccine, 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 virus, and thus cannot cause disease or turn into 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. SiriMr. Kennedy’s advice.

However, it is less important than the almost perfect power of vaccines to prevent paralysis, experts said.

“Yes, yes, it’s true, IPV does not prevent transmission,” said Dr. William Petri, 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 means, however, that people vaccinated with 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 into 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, this is not likely to start an epidemic. 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.

That’s what 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 had been circulating for months, and was later detected in the sewers of several New York counties with vaccination rates hovering around 60 percent, prompting the state to declare an emergency.

Genetically linked polioviruses have been detected in sewage samples in Britain, Israel and Canada, suggesting widespread transmission. Authorities later found two different vaccine-derived type 2 polioviruses in New York sewage, suggesting two separate imports.

If polio were to reappear in the United States, it is unlikely to be as dire as in the pre-vaccine decades. Many older adults still remember that as children they were not allowed to swim in rivers or pools, or anywhere the virus could settle.

“The reason we weren’t allowed to play in the rivers in the ’50s is that raw sewage was being dumped into the rivers,” said Dr. Heymann.

That’s no longer the case, so “there won’t be a massive broadcast immediately in the United States,” he added.

But even if a few children become paralyzed, “it would be terrible.”