For preventive measures a clove of garlic a day and Echinacea will boost your immune system. The garlic in your bloodstream is a direct anti-biotic and anti-fungal too. It won't kill viruses but if you reduce bacteria and fungi your immune system will be less stressed if it has to deal with a virus.
Now, get thee up to the attic, Spider Woman!
Soon as somebody puts the new attic stairs up I will.