Dr Ludwik Fleck, who fled to Israel from Poland in 1957, made a groundbreaking discovery of a vaccine for typhus whilst a prisoner in the Nazi’s Buchenwald concentration camp during WWII. He managed to fool the Nazis and vaccinated many thousands of Jews.

https://www.aish.com/jw/s/How-an-Imprisoned-Jewish-Doctor-Invented-a-Typhus-Vaccine-in-Buchenwald.html