I guess the writers postponed the next season significantly because they hoped the pandemic stops by then and they can make some snarky coronavirus references from Fallon's mouth. I guess they are disapointed it hasn't ended yet and the jokes would be out of place.
Otherwise I can imagine Fallon and Adam deliberately caughing at each other saying "You have a corona", "No, you have it now" and then both get isolated.
Yes, that already occurred. I remember thinking "Who throws Pepto-Bismol at a protest?" I can't recall the exact context, but I recall some social-media backlash where she was being called "the new Queen of Mean".