I just got some vaccines, and I have to say they're pretty great. You get the advantage Immunity: (Common Diseases), in exchange for some temporary soreness. Anyone in an RPG would automatically take that offer, if they could somehow be assured that there was no conspiracy behind it. (Note, there is literally no way you could convince players that anything is safe once they get suspicious.)
It tells us something interesting that so many people decline this exact offer when offered it in real life. People's laziness and intellectual self-deception somehow result in people making less rational decisions when the stakes are much higher.