Oh damn. this is why I've been getting small cold and flu the last couple weeks. Normally against these things I'm bulletproof. I don't remember getting sick the last two years until now.
One "coach education" seminar we had on training, muscle building, and recovery from training back in the early 90s told us of the link between the immune system and recovery from training.
Al Reed, then of the University of Ottawa, said that research into the immune system prompted by AIDS research showed/discovered that it was the immune system which was responsible for re-building the body/muscles after training, at night, while in (I forget which) one of the deeper phases of sleep. He said it relies on blood sugar to do the work of rebuilding (of course with amino acids and everything else that goes into building muscles and other tissues). Which is why a glass of juice or a piece of fruit when you get up in the morning is so helpful - quick re-boot of the blood sugar that had been lowered by the 'recovery from training' process.
So if your immune system is necessary for fighting off bugs, and it's necessary for rebuilding after training, it's a good idea to look after yourself, perhaps ease up on the training if you're feeling a bit 'buggy' and perhaps be a little more careful of hand-to-mouth hygiene.
FWIW, if you wear glasses it's actually helpful - a cardiology research nurse (parent of one of the kids I coach) has said that the quickest ingress to your body for airborne virus is by contact with your conjunctiva (the white bits of your eyeballs). Glasses form a physical barrier.
All that's "what I've been told by people who are experts in the field" - not my reading in peer-reviewed literature...
and on, and on, and on...