Oh I see, sorry, Gargle TCP then, should do the same thing. Vitamin B12 has been shown to help with colds both their duration and stopping you from getting them in the first place, have a few marmite sandwiches, should give you about 150% of your RDA.
The importance of Vit C though is greatly overrated, I have it on good medical authority that it's supposed benefits are not supported by medical trials. the story of the rise of Vit C though is a long and interesting one.