The polio vaccine was first used in the early 1950s. The first effective polio vaccine was developed by Jonas Salk and his team in 1952. After initial testing, the vaccine began large-scale use in February 1954 with American schoolchildren. The results of the first major field trials were announced on April 12, 1955, confirming the vaccine's effectiveness. Following licensure in 1955, mass vaccination campaigns began, leading to a dramatic decline in polio cases in the United States and worldwide.