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
A Little Frog Is looking for His Father no a father. Then The Little Frog says to The Little Grasshopper, "Do not cry. I'll be Your Dad..." A Little Frog Is looking for His Father A Little Frog Is looking for His Father () is The 1964 Soviet Russian Stop-motion Animation Film by Roman Kachanov. This Film produced by Soyuzmultfilm studio. The Little Frog looking for, but can not find a dad, who can protect him and play with him. He meets a various animals and asks them to become his dad. All these animals are larger than The Little Frog. An animals do not want to become