Hypertonic saline sprayed up the nasal passages may, at the very first onset, help retard absorption of the viruses that cause colds.
Just recovered from a bit of a stinking case of the lurgy myself. Think I got it from my old man (the fuckin' git...thanks a bloody bunch dad!)
Nothing that some rest and a few shots of oxycontin didn't see off though. Athough it's left behind a bugger of a persistent cough, I can't get rid of it. Although granted my chest isn't tip tip brand spanking new functioning, after that phosgene incident, and innumerable releases of Cl2, SO2, and NOx,