Vaccines contain proteins (antigens) which come from the micro-organisms that cause the diseases they are aimed at preventing. Some vaccines contain whole micro-organisms which are killed or are altered so as not to cause disease. These then stimulate the body into producing antibodies and special white cells that will fight the infection if it appears in the future.
There are two main types of vaccine:
Live "attenuated" vaccines (measles, mumps, rubella, poliomyelitis). These are solutions of the micro-organisms which have been altered in such a way as to render them incapable of producing the original disease, but capable of stimulating an immune response. These are the most successful types of vaccines, generally providing life-long protection.
Killed vaccines (Hepatitis B, diphtheria, tetanus, whooping cough, influenza). These are solutions of dead micro-organisms which can still produce an immune response. They include inactivated bacterial toxoids (eg tetanus), whole or partial virus preparations (eg flu) and proteins made by recombinant DNA technology (eg Hep B). They require a primary course of immunisation, usually two to three injections spaced at intervals. Often booster immunisation is needed approximately every five years if immunity is to be maintained.
Reviewed by Dr Diana Hardie, Clinical Virologist employed jointly by the University of Cape Town and the National Health Laboratory Service (NHLS)
Reviewed May 2007