Hilary Koprowski he is chair of the department of radiation oncology at Christiana Hospital in Delaware. While at Lederle Laboratories, Koprowski created the world's first polio vaccine, based on an orally administered attenuated polio virus. In researching a potential polio vaccine, he had focused on live viruses that were attenuated (rendered non-virulent) rather than on killed viruses (the latter became the basis for the injected vaccine subsequently developed by Jonas Salk). Koprowski viewed the live vaccine as more powerful, since it entered the intestinal tract directly and could provide lifelong immunity, whereas the Salk vaccine required booster shots. Also, administering a vaccine
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