Cuba through their respective national academies of sciences, in spite of the fact that the two countries did not have formal diplomatic ties. In 1969–72, he lived in Israel, serving as president of Weizmann Institute of Science in Rehovot. After his return to the United States, he worked (1974–82) as a research professor at the Medical University of South Carolina. He later moved to the Washington, D.C., area, where he was a resident scholar at the John E. Fogarty International Center on the NIH campus in Bethesda, Maryland. Polio research With the menace of polio growing, Sabin and other researchers, most notably Jonas Salk in Pittsburgh and Hilary Koprowski and H. R. Cox in New York City and Philadelphia, sought a vaccine to prevent or mitigate the illness. This was complicated because there were multiple strains of the disease. In 1951, the National Foundation for Infantile Paralysis's typing program confirmed the existence of three main serotypes of poliovirus, since known as type 1, type 2, and type 3. Salk developed an inactivated poliovirus vaccine (IPV), a "dead" vaccine given by injection, which was released for use in 1955. It was effective in preventing most of the complications of polio, but did not prevent the initial intestinal infection. By carrying out autopsies of polio victims, Sabin was able to demonstrate that the poliovirus multiplied and attacked the intestines before it moved to the central nervous system. This also suggested that polio virus could be grown in other tissues besides embryonic brain tissue, leading to easier and cheaper methods of vaccine development. John Enders, Thomas Huckle Weller, and Frederick Robbins would successfully grow poliovirus in laboratory cultures of non-nerve tissue in 1949, an achievement that earned them the 1954 Nobel Prize in Physiology or Medicine. Sabin developed an oral vaccine based on mutant strains of polio virus that seemed to stimulate antibody production but not to cause paralysis. Recipients of his live attenuated oral vaccine included himself, family, and colleagues. Sabin's first clinical trials were carried out at the Chillicothe Ohio Reformatory in late 1954. From 1956–1960, he worked with Russian colleagues to perfect the oral vaccine and prove its extraordinary effectiveness and safety. The Sabin vaccine worked in the intestines to block the poliovirus from entering the bloodstream. Between 1955 and 1961, the oral vaccine was tested on at least 100 million people in the USSR, parts of Eastern Europe, Singapore,