I've been running for twenty years and am currently on a half-year streak with around 15km / day. In all those years I've been sick for about two weeks all in all. Before working out, that was like the average over half a year. Conclusion: Figure out what works for you, have a daily routine, add a bit of obsession and stop reading stories about the pros and cons of exercising.
Same with me during my peak running period last year; even when I was feeling ill or off, a run, albeit grueling at the time, always seemed to aid in my recovery (if only for the placebo of getting myself out of bed). I really need to start doing it on the regular again...
Of course, my nose would be congested again a few hours later, but it was still a decent motivator since I hate taking medicine.
Wish my knee would stop being shitty.