The process of inducing immunity as a preventive measure against infectious diseases. Immunization may be active or passive. In the passive form, antibodies are injected into the blood to provide immediate but short-lived protection against specific bacteria, viruses, or toxins. Active immunization, also called vaccination, primes the body to make its own antibodies and confers longer-lasting immunity. Routine childhood immunization programmes exist for diseases such as diphtheria, pertussis, and tetanus (see DPT vaccination), haemophilus influenza (Hib), measles, mumps, and rubella (see MMR vaccination), meningitis C, and poliomyelitis. Additional immunizations before foreign travel may also be necessary (see travel immunization). Most immunizations are given by injection, and usually have no after effects. However, some vaccines cause pain and swelling at the injection site and may produce a slight fever or flu-like symptoms. Some may produce a mild form of the disease. Very rarely, severe reactions occur due, for example, to an allergy to 1 of the vaccine’s components. Not all vaccines provide complete protection. Cholera and typhoid fever vaccinations, in particular, give only partial protection. People with immunodeficiency disorders, widespread cancer, those taking corticosteroid drugs, or those who have previously had a severe reaction to a vaccine should not be immunized. Some vaccines should not be given to young children or during pregnancy.


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