After World War II the Koprowskis settled in Pearl River, New York, where Hilary was hired as a researcher for Lederle Laboratories, the pharmaceutical division of American Cyanamid. Here he began his polio experiments, which ultimately led to the creation of the first oral polio vaccine. Koprowski served as director of the Wistar Institute, 1957–91, during which period Wistar achieved international recognition for its vaccine research and became a National Cancer Institute Cancer Center.[citation needed]