Answer:
In 1947, Salk received a job at the University of Pittsburgh, where he started carrying analysis on polio, also identified as infantile paralysis. By 1951, Salk had discovered that there were three separate species of polio-viruses and was capable to produce a "killed virus" vaccine for the infection.
That load of anxiety was exalted regularly when it was declared that Dr. Jonas Salk had produced a vaccine upon the disease. Salk grew world-famous late, but his invention was the outcome of several years of painstaking study.