Zinc might help, but there's no evidence that vitamin C or echinacea will ward off a cold. Your best bet is to keep washing your hands thoroughly.
Most people get between two and five colds a year – hence the term "the common cold". Colds are caused by more than 200 different viruses, all of which result in the familiar runny nose, cough and sneezing. Colds can also give you earache, headaches, a sore throat, muscle aches and mild fever. It can be hard to know whether to stay in bed or struggle on and risk infecting colleagues. And since colds can cause sinusitis and ear infections, could you do more to prevent catching one?
For the rest of the story: http://www.guardian.co.uk/lifeandstyle/2012/nov/18/should-i-do-more-to-avoid-cold