He never returned to Poland after the Second World War broke out. As a Pole of Jewish origin, he was in great danger under German occupation. Emigrated, Hilary Koprowski saved thousands of lives with the first vaccine against the polio virus he created after the war.

Hilary Koprowski was a Polish physician. He was particularly interested in viruses and the immune system. In 1939, he finished his medical studies in Warsaw and went to Rome. There, he found the news that Germany had invaded Poland and started the Second World War. Koprowski came from a Jewish family and returning to a country gripped by Nazi terror was therefore extremely dangerous for him.

In 1944, he arrived in the USA, which at the time was struggling to cope with the polio virus and the poliomyelitis caused by it. Even President Roosevelt was ill with it.

Koprowski worked as a professor at the University of Pennsylvania and Thomas Jefferson University in Philadelphia. He conducted research to find a vaccine against polio. He was able to do this during experiments he conducted on Sigmodontinae – rodents from the hamster family. He and his staff took a piece of brain from an infected animal and injected it into another animal. In this way, he obtained a live but significantly weakened virus. Such a vaccine could even be intended for children.

The vaccine was administered for the first time on 27 February 1950. 8 years later, the first mass vaccination with Koprowski’s vaccine took place in the Congo. It was done orally, and more than 250,000 children were vaccinated with it.

In 1951, the vaccine was used in Koprowski’s homeland, Poland. Within four years, the number of polio cases was reduced from more than a thousand a year to 30, and the number of deaths, which had been several hundred in 1959, fell to just two in 1963.