Just like with Covid vaccines, polio vaccines had plenty of serious side effects, and just like with the Covid vaccines, the warnings were ignored. From Peter Skurkiss at americanthinker.com:
Prior to the 1950s, paralytic polio was a scourge. FDR was crippled from it while in his 30s, the March of Dimes was started to combat it, and photos of rows and rows of children in iron lungs were common in the media. From this situation, vaccines were developed to combat the disease.
Polio is caused by one of three types of poliovirus that can cause paralysis and death. In the 1950s, two vaccines were independently developed to combat it, one by Jonas Salk and the other by Albert Sabin. Polio was eradicated, and today those vaccines are thought of as miracle drugs. But were they?
In the early 1950s, Salk was the first to come out with a vaccine. His was designed to treat all three polio viruses at once. His approach seemed basic enough. It was to grow polioviruses in the lab, kill them, and then inject healthy children with the dead viruses. The idea was that the dead viruses could not reproduce, so they could not harm the children. The children’s immune system, however, would detect the injected viruses and produce effective antibodies against them, thus creating immunity against polio.
Just prior to beginning mass inoculations, samples of the Salk vaccine were sent to the National Institutes of Health (NIH) for safety testing.
There, when bacteriologist Dr. Bernice Eddy injected the vaccine into her monkeys, some of them fell down paralyzed. She concluded that the virus was not entirely dead as promised. Instead, the virus was active and could reproduce in its host. Eddy sounded the alarm and presented her findings. A debate ensued in the corridors of power. Advocates for caution were overruled, and the mass inoculation proceeded on schedule.