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
By His Bootstraps By His Bootstraps "By His Bootstraps" is a 20,000 word science fiction novella by American writer Robert A. Heinlein. It plays with some of the inherent paradoxes that would be caused by time travel. The story was published in the October 1941 issue of "Astounding Science Fiction" under the pen name Anson MacDonald; the same issue has "Common Sense" under Heinlein's name. "By His Bootstraps" was reprinted in Heinlein's 1959 collection "The Menace From Earth", and in several subsequent anthologies, and is now available in at least two audio editions. Under the title "The Time Gate", it was also included