Topical one today, Edward Jenner pioneered vaccines in 1798 by creating the first smallpox vaccine based on cow pox, less harmful, it gave protection against small pox. He named it "Vaccine" after the latin for cow "Vacca".
Jewish biologist Ludwik Fleck produced a fake typhus vaccine for the Nazis while providing an effective vaccine for fellow prisoners in Buchenwald Concentration Camp
If I'm remembering right, Jenner tested the vaccine on the expendable
7yr old son of a groom.
Lol, I'd have been more impressed if he had jagged himself.
Different times, I suppose.
Jenner had the idea of injecting the puss from a cow infected with cowpox(it causes postules on the cow's udders) after noticing that no milk maids caugh smallpox. He rightly summised that they were somehow gaining immunity by close contact with cows infected with cow pox.