Immunity is resistance to disease, and is what can be given to a person through DNA, prior contact with the disease, or immunization. A person who suffered chickenpox in childhood has immunity to chickenpox as an adult. A person who received a flu vaccine is immune to the flu. Immunity, however, does not mean that an immunized person can never get sick. Immunity simply makes it much less likely that a person will become ill, and will lessen the conditions if and when a person does become ill.