For many reasons; religion, views... The main reason though was that colonial governments, sensing that it would curb their authority and territorial rights, rejected the plan or chose not to act on it at all.
Answer:In 1947, Salk took a position at University of Pittsburgh, where he began conducting research on polio, also known as infantile paralysis. By 1951, Salk had determined that there were three distinct types of polio viruses and was able to develop a "killed virus" vaccine for the disease.
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