Jonas Salk when the Salk vaccine was introduced, polio was considered one of the most frightening public health problems in the world. In the postwar United States, annual epidemics were increasingly devastating. The 1952 U.S. epidemic was the worst outbreak in the nation's history. Of nearly 58,000 cases reported that year, 3,145 people died and 21,269 were left with mild to disabling paralysis, with most of its victims being children. The "public reaction was to a plague", said historian William L. O'Neill. "Citizens of urban areas were to be terrified every summer when this frightful visitor returned." According to a 2009 PBS
Jonas Salk "I had an opportunity to spend time in elective periods in my last year in medical school, in a laboratory that was involved in studies on influenza. The influenza virus had just been discovered about a few years before that. And, I saw the opportunity at that time to test the question as to whether we could destroy the virus infectivity and still immunize. And so, by carefully designed experiments, we found it was possible to do so." In 1941, during his postgraduate work in virology, Salk chose a two-month elective to work in the laboratory of Thomas Francis at