When there is an epidemic disease, an antiseptic vaccine protects a person from the attack of such an epidemic. Similarly, food offered to Lord Vishnu and then taken by us makes us sufficiently resistant to material affection, and one who is accustomed to this practice is called a devotee of the Lord. Therefore, a person in Krishna consciousness, who eats only food offered to Krishna, can counteract all reactions of past material infections, which are impediments to the progress of self-realization.