Immunization provides resistance, or immunity, to a specific disease-causing agent through antibodies that target and eliminate the agent from the body. Immunity against a specific infectious agent can be acquired passively or actively. Passive immunity involves receiving already-made antibodies from an external source, such as occurs when antibodies are passed from mother to fetus in the womb or via injections of antibody-containing blood products. Active immunity occurs when a person’s own immune system is triggered to generate antibodies against a specific disease-causing agent, such as occurs as a result of infection or vaccination.
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