Small localized paralytic polio epidemics began to appear in Europe and the United States around 1900. Outbreaks reached pandemic proportions in Europe, North America, Australia, and New Zealand during the first half of the 20th century.
By 1950, the peak age incidence of paralytic poliomyelitis in the United States had shifted from infants to children aged five to nine years, when the risk of paralysis is greater; about one-third of the cases were reported in persons over 15 years of age. Accordingly, the rate of paralysis and death due to polio infection also increased during this time.
In the United States, the 1952 polio epidemic became the worst outbreak in the nation's history. Of the nearly 58,000 cases reported that year, 3,145 people died and 21,269 were left with mild to disabling paralysis.