Active immunity occurs when a person develops a permanent immunity to a disease, while passive immunity occurs when a person develops a short-term immunity, according to Infoplease from Pearson Education. Both active and passive immunity can be natural or artificial.
Infoplease explains that natural active immunity is the result of a person being exposed to a live pathogen, developing the disease and then becoming immune to it as a result of the immune response. Artificial active immunity is induced by a vaccine. The vaccine stimulates a primary response against the antigens of the disease without causing symptoms. Infoplease further explains that artificially acquired passive immunity results from short-term immunizations. Naturally acquired passive immunity occurs during pregnancy when antibodies are passed from the maternal bloodstream to the fetal bloodstream.
Immunity is defined as an organism's ability to identify and destroy foreign substances and organisms, according to Infoplease. Mammals are protected by non-specific barriers, such as skin that protects against all foreign substances, and the highly specific response of antibodies. Antibodies are Y-shaped protein molecules that provide immune defense, according to Dictionary.com. Antibody molecules have a unique binding that combines with the binding site of the corresponding antigen of a foreign substance or organism such as a virus. The antibody binds with the antigen to disable it.