Acquired Acquired Immunity -
‘Actively acquired immunity' may be either natural or artificial. Actively acquired natural immunity results from any infection from which a person recovers.

During the infection, antibody production for that specific pathogen is stimulated so that when there is a subsequent infection by either the same or antigenically related pathogen, the antibodies assist in the body's defense.

Actively acquired artificial immunity is the most common method of immunization or vaccination. The immunogens are injected in the body in controlled quantity to stimulate the production of immunoglobulins. Killed and attenuated strains of bacteria and viruses are now used widely for immunization against many diseases (e.g., typhoid, small pox, poliomyelitis, yellow fever, measles, etc.).

Attenuated organisms produce mild infection and induce natural immunity. Vaccines are also being developed now by a variety of other methods involving recombinant DNA technology.