He earned his undergraduate degree in 1915 from Princeton University and received his medical training at Johns Hopkins School of Medicine, which awarded him an M.D. degree.[2] He began his career as an assistant pathologist at Johns Hopkins in 1919 and 1920, and followed that with an internship at Pennsylvania Hospital in Philadelphia from 1920 to 1922.[2] In 1928, Paul joined the faculty of the Yale School of Medicine as a professor of internal medicine and held the position of professor of preventive medicine starting in 1940, which he retained until his retirement.[2] Paul established the Yale Poliomyelitis Study Unit in 1931 together with James D. Trask, advancing the concept of "clinical epidemiology" in which the path of disease outbreaks in small communities was directly studied.[2] Together with Trask, Paul received the first grant from the National Foundation for Infantile Paralysis (better known as the March of Dimes), which was renewed each year for another 30 years.[2] As part of the study unit, Paul went to Middletown, Connecticut and New Haven into neighborhoods where polio was spreading and collected samples from patients in an effort to understand how the virus spread.[3] Paul's team found that poliovirus was excreted by people afflicted with the condition and could be found in sewage in areas that had experienced outbreaks.[2] In a 1951 article published in The New York Times Magazine in 1951, Paul noted the improvements that had been made in treating and relieving pain in those afflicted with polio, but lamented the lack of progress in prevention of polio. He travelled to the Soviet Union in 1956 as part of a group of five doctors who visited medical facilities there.[2]