In the 1950s, the polio virus terrified American families. Parents tried “social distancing”—ineffectively and out of fear. Polio was not part the life they had signed up for. In the otherwise comfortable World War II era, the spread of polio showed that middle-class families could not build worlds entirely in their control.

For the Texas town of San Angelo on the Concho River, halfway between Lubbock and San Antonio, the spring of 1949 brought disease, uncertainty and most of all, fear. A series of deaths and a surge of patients unable to breathe prompted the airlifting of medical equipment with C-47 military transporters.

Fearful of the spread of the contagious virus, the city closed pools, swimming holes, movie theaters, schools and churches, forcing priests to reach out to their congregations on local radio. Some motorists who had to stop for gas in San Angelo would not fill up their deflated tires, afraid they’d bring home air containing the infectious virus. And one of the town’s best physicians diagnosed his patients based on his “clinical impression” rather than taking the chance of getting infected during the administration of the proper diagnostic test, writes Gareth Williams, Paralyzed with Fear: The Story of Polio. The scene repeated itself across the nation, especially on the Eastern seaboard and Midwest.

The virus was poliomyelitis, a highly contagious disease with symptoms including common flu-like symptoms such as sore throat, fever, tiredness, headache, a stiff neck and stomach ache. For a few though, polio affected the brain and spinal cord, which could lead meningitis and, for one out of 200, paralysis. For two to 10 of those suffering paralysis, the end result was death.

Transmitted primarily via feces but also through airborne droplets from person to person, polio took six to 20 days to incubate and remained contagious for up to two weeks after. The disease had first emerged in the United States in 1894, but the first large epidemic happened in 1916 when public health experts recorded 27,000 cases and 6,000 deaths—roughly a third in New York City alone.

After rabies and smallpox, polio was only the third viral disease scientists had discovered at the time, writes David Oshinksi in Polio: An American Story. But a lot remained unknown. Some blamed Italian immigrants, others pointed to car exhausts, a few believed cats were to blame. But its long incubation period, among other things, made it difficult even for experts to determine how the virus transferred.

The prevalence of polio in late spring and summer popularized the “fly theory,” explains Vincent Cirillo in the American Entomologist. Most middle-class Americans tended to associate disease with flies, dirt and poverty. And the seasonal surge of the disease in summer and apparent dormancy in winter matched the rise and fall of the mosquito population.

After World War II, Americans doused their neighborhoods, homes and children with the highly toxic pesticide DDT in the hope of banishing polio, Elena Conis reports in the journal Environmental History. Yet, the number of cases grew larger each season. There were 25,000 cases in 1946—as many as in 1916, writes Oshinski—and the number grew almost every year up to its peak of 52,000 in 1952.

There were signs of hope. The 1930s had seen significant improvements in the iron lung, a negative pressure chamber that could assist the breathing process for severely paralyzed patients. The March of Dimes organization campaigned aggressively to fund the development of a vaccine. And the comparable odds of contracting the disease remained small, the odds of long-term consequences minute, to say nothing of death.

The Journal of Pediatrics, parenting guru Benjamin Spock, every expert and most editorial boards warned against irrational “polio hysteria.” And yet, Oshinski tells us, headlines and images of polio victims were familiar features on the front pages in the summer months. American parents were petrified. A 1952 survey found that Americans feared only nuclear annihilation more than polio.

The random pattern the disease struck made parents feel helpless, as was the lack of a cure. As middle-class parents saw it, something like this was not supposed to happen. Infectious disease had been the leading cause of death in 1900, it was no longer in 1950. They had survived the Great Depression, fought and won World War II, and returned safely from a dangerous world. Oshinski shares this recollection of a journalist from that time: “Into this buoyant postwar era came a fearsome disease to haunt their lives and to help spoil for those young parents the idealized notion of what family life would be. Polio was a crack in the fantasy.”

By 1955 epidemiological evidence had clearly established that mosquitoes and flies played no important role in polio epidemics and Jonas Salk had announced he’d developed a polio vaccine, making the issue moot. Today, new cases of polio have largely been eliminated in the United States. Salk was awarded the Presidential Medal of Freedom in 1977.