Since the late nineteenth century, there had been a number of small, localized outbreaks of poliomyelitis, a viral disease commonly known as infantile paralysis, or polio. Though many recovered from the virus, it carried with it the risk of death or disablement. The first epidemic in the United States took place in 1916, beginning with several cases in Brooklyn, New York. Over 6,000 people died, with one-third of the deceased in New York City. The disease disproportionately affected children. Of the 717 polio cases in Philadelphia during the outbreak, 456 were children between the ages of six months and three years.
By the 1940s and 1950s, polio had emerged as an epidemic. Outbreaks occurred nearly every year, usually in the summer months. Although the disease was more likely to cause paralysis in adults, parents were extremely fearful of exposure. With no cure, they attempted prevention by removing their children from communal spaces, such as public pools and movie theaters.
In 1952, among the worst years of the polio epidemic in the US, Jonas Salk tested the first polio vaccine. A large, widely publicized field trial in 1954 involved the participation of 1.8 million children in elementary schools across the country. The tests showed the vaccine to be safe and effective, and, in 1955, a campaign for mass inoculation began.