Final answer:
Active immunization involves introducing a modified or weakened pathogen to trigger an immune response and develop memory cells, leading to long-lasting protection. Passive immunization involves the direct administration of antibodies and offers immediate, short-term protection.
Step-by-step explanation:
Injecting an antigen such as a weakened or killed pathogen is called active immunization, while passive immunization is a type of immunotherapy that involves the administration of preformed antibodies to a person, as opposed to eliciting an immune response through vaccination.
Active immunization is the process by which a person is exposed to a modified form of a pathogen (or part of a pathogen) in order to provoke an immune response and the formation of memory cells without causing sickness. This can be achieved through various types of vaccines such as live attenuated vaccines, inactivated vaccines, subunit vaccines, and recombinant vaccines, all of which expose the person to key antigens of the pathogen.
Passive immunization, on the other hand, provides immediate protection by introducing antibodies from another source rather than inducing the body to produce its own antibodies. It is often used when there is an immediate risk of infection and there is not enough time for active immunization to take effect.