Jonas Edward Salk was an American medical researcher and virologist. He discovered and developed one of the first successful polio vaccines. Born in New York City, he attended New York University School of Medicine, later choosing to do medical research instead of becoming a practicing physician. In 1939, after earning his medical degree, Salk began an internship as a physician scientist at Mount Sinai Hospital. Two years later he was granted a fellowship at the University of Michigan, where he would study flu viruses with his mentor Thomas Francis, Jr.