Three teams engaged in the vaccine race: a) Lederle's, b) Wistar and c) University of Cincinnati.
More fully, these were Lederle Laboratories, Pearl River, NY under Herald Cox, Wistar Institue of the University of Pennsylvania, Philadelphia, PA under Hilary Koproski, and Microbiology of the University of Cincinnati, Cincinnati, OH under Albert Sabin. The Lederle's attenuated strains has been under development since 1946 by Cox & Koprowski.
Stanley Plotkin then at Wistar worked with Chat 1 in the Belgian Congo, even though such regions are often high in natural antibodies. At
least the Congo was free of Sabin and Salk antibodies that would have
caused epidemiologic confusion.