Hilary Koprowski was born in Warsaw, Poland, to Paweł (Paul) and Sonia Koprowski. The parents had met in 1906 while Hilary Koprowski’s father was serving in the Russian Army, and they had moved to Warsaw soon after their marriage in 1912. Hilary Koprowski attended Warsaw’s Mikołaj Rej Secondary School, and from age twelve he took piano lessons at the Warsaw Conservatory. He received a medical degree from Warsaw University in 1939. He also received music degrees from the Warsaw Conservatory and, in 1940, from the Santa Cecilia Conservatory in Rome. He adopted scientific research as his life’s work, but never gave up music and composed several musical works. In July 1938, while in medical school, Koprowski married Irena Grasberg.  In 1939, after Germany’s invasion of Poland, Koprowski and his wife, likewise a physician, fled the country, using Koprowski family business connections in Manchester, England. Hilary went to Rome, where he spent a year studying piano at the Santa Cecilia Conservatory; while Irena went to France, where she gave birth to their first child, Claude Koprowski, and worked as an attending physician at a psychiatric hospital.

As the invasion of France loomed in 1940, Irena and the infant escaped from France via Spain and Portugal —where the Koprowski family reunited — to Brazil, where Koprowski worked in Rio de Janeiro for the Rockefeller Foundation. His field of research for several years was finding a live-virus vaccine against yellow fever.  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.

Koprowski died on April 11, 2013, aged 96, in Wynnewood, near Philadelphia, Pennsylvania, of pneumonia.  Hilary Koprowski and his late wife are survived by two sons, Claude (born in Paris, 1940) and Christopher (born 1951). Claude Koprowski is a retired physician. Christopher Koprowski is a physician certified in two specialties, neurology and radio-oncology; 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 by mouth is easy, whereas an injection requires medical facilities and is more expensive.

Koprowski developed his polio vaccine by attenuating the virus in brain cells of a cotton rat, Sigmodon hispidus, a New World species that is susceptible to polio. He administered the vaccine to himself in January 1948 and, on 27 February 1950, to 20 children at Letchworth Village, a home for disabled persons in Rockland County, New York. Seventeen of the 20 children developed antibodies to polio virus — the other three apparently already had antibodies — and none of the children developed complications. Within 10 years, the vaccine was being used on four continents.

Albert Sabin’s subsequent attenuated-live-virus polio vaccine was developed from attenuated polio virus that Sabin had received from Koprowski.  Koprowski was President of Biotechnology Foundation Laboratories, Inc., and Head of the Center for Neurovirology at Thomas Jefferson University.  In 2006 he was awarded a record 50th grant from the National Institutes of Health.  He authored or co-authored over 875 scientific papers and co-edited several scientific journals.  He served as a consultant to the World Health Organization and the Pan American Health Organization.