RFK Jr.'s key advisor petitioned to revoke approval of the polio vaccine. Photos show the US's last outbreak.

Polio mainly affects children under the age of five. Most people only have mild symptoms, but one in 200 cases causes irreversible paralysis. Between 5% and 10% of paralyzed patients die when muscles used for breathing can no longer move, according to the World Health Organization. 

Polio was first identified in 1909, though it had been around for centuries, and the US had a serious outbreak in 1916, which started in New York. 

At the time, doctors understood very little about the disease, including how to treat and prevent it. 

An estimated 6,000 people died and 21,000 had resulting paralysis from the 1916 outbreak.

The number of polio cases rose from eight per 100,000 in 1944 to 37 per 100,000 in 1952, according to Yale Medical Magazine. During that period, about 60,000 children were contracting the disease each year.

There was an increase in people over the age of 10 getting the virus, too. 

Early on, some doctors would put patients in full-body casts, which could make paralysis permanent. 

Roosevelt sought relief by taking dips in Georgia's warm springs. 

During a 1940s polio outbreak, the Hickory Emergency Infantile Paralysis Hospital in North Carolina tried treating patients with boiled wool "hot packs" for the skin and physical therapy.

Bellows inside the large metal box provided suction to help patients breathe when they could no longer do so on their own. The device was first used to save the life of an eight-year-old patient in 1928. 

Farrow, the daughter of director John Farrow and the actress and Tarzan-girl Maureen O'Sullivan, became ill during an LA polio outbreak in the summer of 1954.

"What I saw will never leave me — in the hospitals and in the public wards for contagious diseases," Farrow said in 2000. 

Roosevelt founded the organization with his former law partner, Basil O'Connor, to help fund research into a polio vaccine. 

Roosevelt knew the effects of polio first-hand. He was diagnosed with polio in 1921 at the age of 39 and used a wheelchair, mainly in private, while he was president. 

These campaigns helped raise half of all donations to health charities in the US, PBS reported.

At the University of Pittsburgh School of Medicine, Salk began developing a vaccine in the early 1950s.

He grew polioviruses on cultures of monkeys' kidney cells and then used formaldehyde to kill the virus.

When he injected the dead virus into live monkeys, it protected them from the disease, according to the Science History Institute.

Salk first injected children who had already had polio. He noted that their antibody levels rose after vaccination, a promising sign that it helped the body fight the infection. 

In the early 1950s, over 220,000 children were injected with gamma globulin, proteins in blood plasma that are rich in antibodies. The hope was that the serum would boost kids' immune systems and keep them from contracting polio. 

After looking at the data, though, a committee of epidemiologists and other experts concluded that gamma globulin wasn't effective. 

In 1954, the National Foundation for Infantile Paralysis sponsored a trial to test Salk's vaccine. 

Nearly 2 million children between 6 and 9 years old participated. They were called "Polio Pioneers."

Participants were divided into three groups: the first group received the vaccine, the second received a placebo, and the third received neither the vaccine nor a placebo. 

The following year, in 1955, the vaccine was declared 90% effective against Types 2 and 3 poliovirus. It was 60% to 70% effective against Type 1.

At a press conference, Thomas Francis Jr., director of the Poliomyelitis Vaccine Evaluation Center at the University of Michigan, called the vaccine "Safe, effective, and potent."

It was headline news. "The story has blanketed the front pages of all the papers I have seen along a 1,600-mile route from New York to Saint Louis, to Memphis and Dallas," Alistair Cooke reported for The Guardian at the time. 

It took mere hours for Salk's vaccine to be licensed for use after the announcement of its efficacy.

NFIP had already funded facilities that could start producing the vaccine right away. The US sent some vaccines to Europe, and some countries started up their own productions. 

Children needed three shots, each costing between $3 and $5 (around $35-$59 today), according to The Conversation.

One of the facilities manufacturing the vaccine, Cutter Laboratories, had kept the live polio virus in hundreds of thousands of doses.

In April 1955, over 400,000 children received the improperly prepared vaccines. The mistake led to 260 cases of polio-based paralysis and several deaths, according to the National Institutes of Health. 

The incident at Cutter Laboratories panicked many parents and the vaccine was pulled from the market on April 27, 1955. 

However, after a massive effort to recheck all the vaccines confirmed they were safe to use, immunization resumed on May 15, 1955. Worldwide, hundreds of thousands of children received the vaccine. 

If people were hesitant to have their children vaccinated, Elvis may have helped persuade them. After he got the jab in the fall of 1956, many followed suit. 

Within six months, 80% of America's youngest generation were vaccinated, Scientific American reported in 2021. 

Roosevelt's foundation was heavily involved in promoting the vaccine and recruited celebrities like Louis Armstrong and Ella Fitzgerald for their campaigns.

"There was a very early recognition that you couldn't just have white people talking about the vaccine,"  Stacey D. Stewart, former president and CEO of the March of Dimes, told NPR in 2021. 

Between 1953 and 1957, cases in the US dropped from 35,000 to 5,300 a year, according to the BBC.  

Sabin disagreed with Salk's method of using a vaccine with a killed virus. Instead, he preferred a live, yet weakened form that could be taken by mouth instead of injected. 

Once Sabin showed his version was effective using a trial in the Soviet Union, it was approved for use in the US in 1961.  

Because Sabin's vaccine was inexpensive and easy to administer many countries began using the oral method. In fact, the song "A Spoonful of Sugar (Helps the Medicine Go Down)" in the 1964 film "Mary Poppins" was inspired by Sabin's polio vaccine.

During the 2010s, the world eradicated polio Types 2 and 3. Only Type 1 remains. The World Health Organization hopes to wipe out the final strain by 2026, but that goal is impossible without polio vaccines. 

This story was originally published on August 13, 2022, and updated on December 16, 2024. Jake Johnson contributed to a previous version of this post.