This stuff varies per person anyway. We do after all have immune systems, and in most people they work pretty well. Especially if you've had prior exposures to pathogens you're encountering again, and have recovered.

Sickness varies per person too. I've done strenuous long distance hikes with, sufficie to say, "stomach trouble" and survived just fine. Other people who are in even worse shape than me wouldn't have done so well. I also have a pretty high tolerance for things sucking before I really complain, at least while hiking. 😂