“The supplements, remedies and cereals that claim to strengthen immunity (and thereby protect you from colds) do no such thing. It would be one thing if by some magic they made your body produce antibodies to any particular virus. But they don’t.”
The quote comes from Jennifer Ackerman, author of Ah-Choo!: The Uncommon Life of Your Common Cold, who wrote a NY Times op-ed just in time for cold and flu season.