springles, this is what I found on kellymom:
The best thing you can do for your baby when you're sick is to continue to breastfeed. When you have a contagious illness such as a cold, flu, or other mild virus, your baby was exposed to the illness before you even knew you were sick. Your milk will not transmit your illness to baby, but it does have antibodies in it that are specific to your illness (plus anything else you or baby have been exposed to) - they'll help prevent baby from getting sick, or if he does get sick, he'll probably not be as sick as you.
Withholding your breastmilk during an illness increases
the possibility that baby will get sick, and deprives baby
of the comfort and superior nutrition of nursing.