Polio vaccine attenuated vaccine strains. In 1958, the National Institutes of Health created a special committee on live polio vaccines. The various vaccines were carefully evaluated for their ability to induce immunity to polio, while retaining a low incidence of neuropathogenicity in monkeys. Large-scale clinical trials performed in the Soviet Union in late 1950s to early 1960s by Mikhail Chumakov and his colleagues demonstrated safety and high efficacy of the vaccine. Based on these results, the Sabin strains were chosen for worldwide distribution. Fifty-seven nucleotide substitutions distinguish the attenuated Sabin 1 strain from its virulent parent (the Mahoney serotype), two nucleotide substitutions
Polio vaccine testing outside the United States, Sabin in Mexico and then in the Soviet Union, and Koprowski in the Congo and Poland. In 1957, Sabin developed a trivalent vaccine, containing attenuated strains of all three types of poliovirus. In 1959, ten million children in the Soviet Union received the Sabin oral vaccine. For this work, Sabin was given the medal of the Order of Friendship Among Peoples, described as the Soviets' highest civilian honor, despite having become an American during the height of the cold war. Sabin's oral vaccine using live virus came into commercial use in 1961. Once Sabin’s oral