First of all, I cannot think of any medical condition that would necessitate the taking of zinc or even why it it is beneficial as a supplement.........seen, in a lifetime of general medical practice.
I haven't had a cold in many many years- even when the rest of the family has. It does seem to be about immune response (mostly about oestrogen). Keeping yourself well and healthy in general is about as much as you can do, although will still not guarantee against viruses.