You are hanging out at an amazing science facility–something like Star Labs–and you’re holding in your hand a newly-developed antibiotics gun. It can inject a person with a special capsule that will slowly release a full course of antibiotics, then, once the course is done, the capsule itself is absorbed by the body. A full cure in one dose.
A friend of yours comes by–she’s a little drunk. She and her colleagues have been celebrating the creation of a time window, which would let you see into any place or time on the planet Earth, and also let you pick something up or send something back.
While you’re getting over your envy of the magnificence of their creation, your friend gets excited. She could open a time window and you could shoot a full course of antibiotics into anyone in history. You could cure John Keats of his tuberculosis, if you wanted!
You mention the dangers of changing history, and your friend suggests that would be honestly difficult. If you cured Typhoid Mary, yes, a whole lot of people would have lived rather than died, and that might change things. If you cured John Keats or Immanuel Kant, you would end up with some more interesting things to read. It’s perfectly safe with a careful choice!
Do you want to cure someone in the past? Who would it be, and when?