In some clinical trials, participants get infected with who knows what.
Sure, sometimes it's just common cold viruses, but other times it's stuff like typhoid, malaria, cholera, COVID, and a bunch of other things.
Obviously, it's not a fun experience - so why do people take part in these studies?
And how do we handle all this from an ethical standpoint? A big article in Undark tries to tackle these questions:
https://undark.org/2021/04/07/getting-sick-for-medical-research/