Active immunization is that in which an antigen penetrates the body triggering the primary immune response and the production of memory lymphocytes and antibodies that provide faster and more effective immune defense in future infections by the same antigen. Passive immunization is that in which immunoglobulins against an antigen are inoculated in the body to provide protection in case the body becomes infected by the antigen.
Active immunization tends to be longer lasting than passive immunization since in the active type as well as antibodies, specific memory lymphocytes remain in the circulation. In the passive immunization the duration of the protection is that of the duration of the antibodies in the circulation.