Active immunity:
The individual alone produces antibodies against an antigen. Active immunity is slow and takes time to give its full effective response. Usually active immunity is long lasting. Sometimes active immunity develops naturally when infectious organisms gain access into body during natural infection.
Passive immunity:
Readymade antibodies are given directly to protect the body against foreign agents. Antibodies can be injected by a physician. Passive immunity is temporary because antibodies are not produced by the person's plasma cells. Thus passive Immunity gets help from the outside, as the person is given prepared antibodies using an injection.
During the initial days of lactation, the yellowish fluid colostrum secreted by mother has IgG and IgA antibodies to protect the infant. Thus breast-feeding is an example of natural passive immunity. Also during passive immunity, antibodies are received by crossing the placenta, as antibodies (IgG) cross the placenta in case of a pregnant woman. Thus the fetus will receive passive immunization against prevalent pathogens.
