The competition to find a polio vaccine began in 1938, when Franklin D Roosevelt (himself stricken with the disease) founded the National Foundation for Infantile Paralysis. Jonas Salk, who would develop the first injectable vaccine, concentrated on dead polio virus. Koprowski, though, reasoned that a live but weakened (or attenuated) form of the virus would more closely mimic an actual polio infection.
Many scientists were wary of using the live virus, fearing that even in its weakened state it might still be dangerous. But in January 1948 Koprowski gulped down a preparation made with ground-up cotton-rat brain infected with attenuated polio virus. He survived, and two years later 20 boys and girls at a home for children with learning difficulties were given doses of the same mixture, with no ill effects.
When Koprowski presented his results at a conference in 1951 there was widespread disbelief. But his research caught the attention of Albert Sabin who, in 1955, won the race to get a live-virus vaccine licensed in the United States.
While Salk and Sabin became public figures for their achievement in all but eradicating polio, Koprowski had to fight off allegations that his vaccine trials had launched the global Aids epidemic. In his 1999 book The River: A Journey to the Source of HIV and Aids, the British journalist Edward Hooper suggested that during trials of Koprowski’s vaccine in the Congo in the late 1950s the vaccine had become contaminated with the chimpanzee version of the Aids virus, introducing the infection into the human population. In 2000, however, a special meeting of the Royal Society comprehensively debunked the theory, while tests on Koprowski’s original vaccine samples found no evidence of either chimp cells or any HIV-like virus.
An only child, Hilary Koprowski was born in Warsaw on December 5 1916. A gifted musician, he entered the Warsaw Conservatoire aged 12 and might well have become a concert pianist had he not concluded that he could never be as good as another brilliant piano player in his class.
Instead he switched to Medicine, studying at Warsaw University, where he met his wife, Irena Grasberg. They married in 1938 and, after the Nazi invasion the following year, fled Poland. Hilary went to Rome, where he spent a year at the National Academy of Santa Cecilia, and Irena to France. In 1940 they reunited in Portugal and went to Brazil, where Koprowski worked for the Rockefeller Foundation researching a vaccine against yellow fever.
After the war the Koprowskis settled at Pearl River, New York, where Koprowski became a researcher at Lederle Laboratories, working on the polio vaccine. He served as director of the Wistar Institute in Pennsylvania from 1957, then as director of the Biotechnology Foundation Laboratories at Thomas Jefferson University from 1991 to 2011.
Under Koprowski’s leadership, scientists at Wistar developed the rubella vaccine and a vaccine against rabies that has proved more effective and less painful to inject than the traditional Pasteur vaccine. In the 1970s Koprowski became a pioneer in the field of monoclonal antibodies, which are now used to detect and fight cancer. At Jefferson, he worked on genetically engineering plants to carry vaccines.
But he was never an easy colleague. In 1991 he was fired by the Wistar Institute, which had been haemorrhaging money, and subsequently went to court claiming age discrimination. In 2010, after Jefferson reduced his office space following a cut in funding, he went to court again, claiming that the university was violating disabilities legislation by ignoring his age-related needs.
Koprowski was a member of the National Academy of Sciences and the American Academy of Arts and Sciences and was appointed to the French Legion of Honour.
His wife died last year, and their two sons survive him.
Hilary Koprowski, born December 5 1916, died April 11 2013