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With regard to Philadelphia, the reason for using chimpanzee cells advanced by the book is that there were difficulties in obtaining rhesus cells during 1957–1960 because of exportation bans by India. Joe Held, a retired veterinary primatologist who was active at that time, comments as follows in a letter to me dated 20 March 2000: I was in the Koprowski laboratory from August 1957 through June 1961, and never received, worked with, or saw others working with cells from chimpanzees.Macaque cells in suspension or in monolayer were regularly received from Microbiological Associates, a commercial laboratory.
Mass vaccination campaigns were undertaken in the Congo, starting in February 1957 in various villages in northeastern Congo where polio infections were occurring, and leading up to a major campaign in the Ruzizi Valley that was conducted February–April 1958 .
The precursors of the Sabin strains were those developed by Hilary Koprowski, first at the Lederle Laboratories and then at the Wistar Institute in Philadelphia.
The results of the first administration of OPV to humans were published by Koprowski et al.
Testimony by eyewitnesses, historical documents of the time, epidemiological analysis, and analysis of ancillary phylogenetic, virological, and polymerase chain reaction data all indicate that this hypothesis is false.
Poliomyelitis is rapidly disappearing from the world, thanks in large part to the widespread use of the oral polio vaccine (OPV) strains developed by Albert Sabin.