Two vaccines are used throughout the world to combat polio. The first was developed by Jonas Salk, first tested in 1952 using the HeLa cell, and announced to the world by Salk on April 12, 1955. The Salk vaccine, or "inactivated poliovirus vaccine" (IPV), consists of an injected dose of killed poliovirus. In 1954, the vaccine was tested for its ability to prevent polio; its field trials grew to be the largest medical experiment in history. In 1955, it was chosen for use throughout the United States. By 1957, following mass immunizations promoted by the March of Dimes, the annual number of polio cases in the United States was reduced, from a peak of nearly 58,000 cases, to 5,600 cases.