The immune system is still not well understood. Vaccinations have certainly changed the course in a few ways. I've always found the story of the pertussis vacci

The immune system is still not well understood. Vaccinations have certainly changed the course in a few ways. I've always found the story of the pertussis vaccine interesting: https://i.imgur.com/v8e8trm.png https://i.imgur.com/v8e8trm.png For one, it's a "vaccine" not against a virus, but a bacteria. More specifically, a toxin produced by the bacteria. Those that have been vaccinated are immune to the toxin, not necessarily the bacteria. So prior to 1950, most people that got whooping cough were around the age of 5. Now the only ones that get whooping cough are infants or the elderly.