Immunization

Immunization is one of the most successful medical interventions ever developed: it prevents infectious diseases worldwide. The basis for its success is that the human immune system can respond to vaccines by producing pathogen-specific antibody and memory cells (both B and T cells) which protect the body should the pathogen be encountered. Most currently licensed vaccines contain live or killed bacterial or viral constituents, bacterial polysaccharides, or bacterial toxoids, while new types of vaccines are being developed that contain DNA. Most vaccines are delivered directly into skin or muscle via needles, or they are administered orally. New edible vaccines and vaccines delivered via the skin without the use of needles are being developed. The Expanded Programme on Immunization, set up by the World Health Organization to define which vaccines should be delivered in resource-poor countries, has done much to increase vaccination coverage among infants most at risk of infectious diseases.