sentences:  In 1954, the vaccine was tested for its ability to prevent polio; the field trials involving the Salk vaccine would grow to be the largest medical experiment in history.Immediately following licensing, vaccination campaigns were launched, 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.Eight years after Salk's success, Albert Sabin developed an "oral polio vaccine" (OPV) using live but weakened ("attenuated") virus.