Salk Inactivated Polio Vaccine Field Trial (Francis Report)

In the early 1950s polio paralyzed close to 20,000 Americans a year, and summer epidemics closed swimming pools and other places where children gathered. The 1952 epidemic was the worst on record, with nearly 58,000 reported cases. The National Foundation for Infantile Paralysis, founded by Franklin Roosevelt, had been funding polio research since 1938, and by 1952 Jonas Salk at the University of Pittsburgh was developing a formalin-inactivated vaccine using all three poliovirus serotypes grown in monkey kidney cells.

The 1954 field trial was organized by the National Foundation and evaluated by Thomas Francis Jr. at the University of Michigan, who had no role in developing the vaccine, although Salk had worked with him on influenza vaccine in the 1940s. Francis set strict conditions for the design. About 1.8 million children took part. In some areas children were randomly given vaccine or a placebo injection, and neither families nor health officials knew which; in others, vaccinated children were compared with unvaccinated children who were only observed.

Francis presented his findings on April 12, 1955, at the University of Michigan in Ann Arbor, ten years to the day after Roosevelt's death. The vaccine was 80 to 90 percent effective against paralytic polio. The National Foundation staged the event with a showmanship that displeased many scientists. The federal government licensed the vaccine that afternoon, and large stockpiles were released immediately.

Within ten days, polio began appearing in children given vaccine from one manufacturer whose lots contained live virus. There were 260 cases, 94 in vaccinated children and 166 in their contacts, and 11 deaths, and vaccination stopped until the cause was found. After it resumed, paralytic polio in the United States fell from close to 20,000 cases a year before the vaccine to about 2,500 in 1960. Albert Sabin's live attenuated oral vaccine, which was easier to give and produced intestinal immunity that blocked transmission, began supplementing the Salk vaccine in the early 1960s. The last case of polio from wild virus acquired in the United States occurred in 1979.

Salk was not an author of the Francis report. In 1988 the World Health Assembly launched the Global Polio Eradication Initiative, when polio was endemic in more than 125 countries; by the 2020s wild poliovirus remained endemic only in Afghanistan and Pakistan.