I've had a crappy night so decided to spawn a world on easy mode - no stress, no infections. I set those things in the custom game settings, and off I went.
Stress acted as I would expect - nothing can stress them out. But infections, while immunity stayed at 100%, all three of my dupes had food poisoning by cycle three.
I don't have the save file unfortunately. Was not in a good place and trashed it I think.
Also, if the arch offers dupes and I accidentally hit escape, and then try and go back immediately, the game crashes. I'm not sure if it will crash if I wait until the set time has gone by and a new set is offered up.
Leave the select dupes screen with the escape button, and set it so the immunity should be invincible.