Active immunization

Active immunization is the induction of immunity after exposure to an antigen. Antibodies are created by the recipient and may be stored permanently.

Active immunization can occur naturally when a microbe or other antigen is received by a person who has not yet come into contact with the microbe and has no pre-made antibodies for defense. The immune system will eventually create antibodies for the microbe, but this is a slow process and, if the microbe is deadly, there may not be enough time for the antibodies to begin being used.