Albert Sabin organized by Soviet scientist Mikhail Chumakov. This provided the critical impetus for allowing large-scale clinical trials of OPV in the United States in April 1960 on 180,000 Cincinnati school children. The mass immunization techniques that Sabin pioneered with his associates effectively eradicated polio in Cincinnati. Against considerable opposition from the March of Dimes Foundation, which supported the relatively effective killed vaccine, Sabin prevailed on the Public Health Service to license his three strains of vaccine. While the PHS stalled, the USSR sent millions of doses of the oral vaccine to places with polio epidemics, such as Japan, and reaped the
Polio vaccine attenuate the Sabin 2 strain, and 10 substitutions are involved in attenuating the Sabin 3 strain. The primary attenuating factor common to all three Sabin vaccines is a mutation located in the virus's internal ribosome entry site, which alters stem-loop structures, and reduces the ability of poliovirus to translate its RNA template within the host cell. The attenuated poliovirus in the Sabin vaccine replicates very efficiently in the gut, the primary site of infection and replication, but is unable to replicate efficiently within nervous system tissue. In 1961, type 1 and 2 monovalent oral poliovirus vaccine (MOPV) was licensed, and