Active Immunization

Active immunization is the induction of immunity that occurs after exposure to an antigen, in which the recipient own body produces antibodies and forms memory cells capable of responding if the same pathogen appears again. It can occur naturally, when a person is exposed to a microbe they have not previously encountered and has no pre-formed antibodies, or artificially, when a treated, weakened or partial form of the microbe is deliberately introduced before natural exposure occurs; vaccination is the most familiar example of artificial active immunization. It differs from passive immunization, in which ready-made antibodies are transferred into the body rather than produced by it.