13/08/2026
One of the biggest clinical trials in history helped defeat polio.
In the early 1950s, polio was one of the most feared diseases in the world: causing nearly 60,000 cases a year in the U.S. alone, with around a third of those affected left paralysed.
In 1954, scientists set out to test something that could change everything: a new vaccine developed by Jonas Salk.
To find out if it worked, over 1.8 million children across the United States took part in the trial, making it one of the largest clinical trials ever conducted. Hundreds of thousands of children received either the vaccine or a placebo, while over a million more were studied as part of the research.
It wasn't just doctors and scientists involved: an incredible 325,000 volunteers, including nurses, teachers, and everyday citizens, helped run the trial. There was no technology involved either: results were tracked by hand, using pencils and paper.
When the results came in the following year, they showed the vaccine was 80–90% effective at preventing paralytic polio: a huge breakthrough that helped protect millions of children around the world.
This trial laid the groundwork for how large-scale clinical trials and vaccine studies are still run today.
*Source: Meldrum M. "A calculated risk": the Salk polio vaccine field trials of 1954. BMJ. 1998;317(7167):1233-1236.*
