The process of immunization or vaccination capital-izes on the functions of lymphocytes and is based on passive immunity. It also relies on the primary and sec-ondary responses of active immunity described earlier.
An individual can be immunized in emergencies by injecting large quantities of antibodies (produced outside) against the specific disease. For example, in a cholera epidemic, a large population may need to be immunized quickly before the disease spreads. In this case, direct injection of antibodies provides a temporary form of immunity. Rh-negative mothers carrying Rh-positive fetuses are routinely given anti-bodies against Rh antigens soon after delivery. These antibodies protect against Rh antigens that may have leaked into the mother’s circulation from the fetus. If antibodies do develop, they can attack the next Rh-positive fetus and jeopardize its life. These are both examples of passive immunization, in which the in-dividual’s immune system is not stimulated to pro-duce his or her own antibodies.
In active immunization, by being exposed to the spe-cific antigen, the individual produces his or her own antibodies. The antigen may be in the form of small quantities of pathogens that are similar to but not as lethal as the one producing disease. Or, the antigen could be in the form of killed pathogens. Such vac-cines have been developed against many diseases. Vaccines against diseases such as diphtheria, polio, tetanus, whooping cough, and measles are routinely given to children. Many of these vaccines are given more than once to stimulate a secondary, long-lasting response to the antigen.
Rarely, some forms of immunization procedures produce adverse effects. Methods are available to identify those children prone to develop these rare adverse effects; parents must make an informed choice about immunization in these cases.
If a large population of individuals who have not been immunized against a particular infection exists in one area, the entire population becomes vulnera-ble to that infection. In these situations, an epidemic of that particular disease can eliminate the entire population. Presently, such a situation has not risen as those who have been immunized are shielding in-dividuals who have not been immunized from con-tracting these deadly diseases.