A couple of things that might help fight colds and flu that I thought would be useful to share.
We use something called Sambucol which is made from black elderberry and has apparently been researched and found to be effective in helping fight off flu. There is lots of info on the net but here are a couple of bits here and here . You can buy it at health food shops but also Boots and Tesco. We have never tried it with flu but have used it when ds has had a cold and it seems to have worked at lessening the symptoms and duration.
The other thing I have started using to boost immunity during the flu season is Lactoferrin. Again lots of info on the net but some info here Only just started this so no results as yet.