Of late I have been walking a lot, especially since the UK had had such a mild winter (I nearly wrote Summer!). Managed to avoid a lot of rain one way or another. Nose constantly drips, and I always have a stash of those little packets of tissues, buy them dozen a pop. And I haven't had much more than a deep voice for a year.

This is much like a colleague once told me how he trained for marathons daily and never had a cold per se, just constant sniffles. Until he had to stop and he suffered the mother of all colds.

What might be happening is that you are exposed to every thing going at an early stage and in doses that the immune system can keep up with. So the immune system sees all the evolutions of the bugs as they spread. I also use public transport a lot and dance every Saturday - more exposure.