First Successful Polio Vaccine

In 1952, the American physician and researcher Jonas Salk completed the development of an inactivated polio vaccine and began testing it in people. It was the first vaccine to offer real protection against a disease that had terrified families around the world, and its eventual rollout helped turn polio from a recurring seasonal dread into a largely preventable illness.

Poliomyelitis is caused by a virus that spreads mainly through contaminated food, water, and contact with fecal matter. Most infections cause few or no symptoms, but a small share attack the nervous system and can cause paralysis or death. In the early twentieth century, epidemics grew more frequent and severe in industrial countries, often peaking in summer. The United States saw particularly large outbreaks in the late 1940s and early 1950s, with tens of thousands of cases in the worst years. Parents kept children away from pools and crowds, and images of children in leg braces or iron lungs became familiar. President Franklin D. Roosevelt, who was paralyzed by an illness diagnosed as polio, helped inspire the National Foundation for Infantile Paralysis, which later became the March of Dimes and funded much of the research.

Salk, working at the University of Pittsburgh with foundation support, pursued a "killed-virus" approach. Researchers had by then learned to grow poliovirus in cell cultures, and they knew there were three virus types. Salk's team prepared vaccine from virus inactivated with formaldehyde, aiming to trigger immunity without causing disease. In 1952 he began trials on small groups, including children who had already recovered from polio, and later extended them to others, with early results showing the vaccine raised antibody levels.

The decisive proof came in 1954, when a very large field trial, organized by the National Foundation and evaluated by Thomas Francis Jr., enrolled well over a million schoolchildren. In April 1955 the results were announced as showing the vaccine was safe and effective, prompting national celebration and a licensing decision the same day. Soon afterward, the "Cutter incident," in which improperly inactivated vaccine from one manufacturer caused cases of paralysis, led to tighter safety regulation.

Salk's vaccine was followed by Albert Sabin's oral vaccine, which used weakened live virus and became widely used from the early 1960s because it was cheap and easy to give. Vaccination campaigns drove polio cases down sharply in many countries, and the disease was eliminated from the Americas in the late twentieth century. A global eradication effort began in 1988, and wild poliovirus now persists in only a few places. Salk is also remembered for declining to patent the vaccine, though historians note that patentability was in doubt anyway.