Abstract
Throughout the 1950s parents greeted each summer with mounting anxiety as outbreaks of polio were responsible annually for 20000 to 25 000 cases of paralytic disease. In 1954, the Francis field trial demonstrated the efficacy of inactivated polio virus vaccine (IPV) in the prevention of this dread infection. Beginning in 1955, widespread use of IPV resulted in a marked decline in the annual reported incidence of polio. In 1959, however, there was an incipient upswing in the number of people contracting polio, a significant proportion of whom had previously received three or more injections of IPV Coupled with the dramatic reports of the success of oral polio virus vaccine (OPV) in Europe and other parts of the world, a shift took place in 1961 in the United States with a transition from the IPV to an OPV program. Soon thereafter, reported cases of paralytic disease due

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