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Explain how a vaccination can prevent an illness.

A vaccine introduces a dead or inactive pathogen such as components of a virus or bacteria. The host (the person who receives the vaccination) will develop an immune response to this pathogen. The immune response involves white blood cells which will bind to the pathogen and produce antibodies. These antibodies will bind to specific antigens (different types of bacteria and viruses have different antigens on their surface which are specific to that pathogen). If the person became infected by the same type of pathogen again, antibodies will be produced by your ‘memory’ white cells. These antibodies are produced very quickly and in large amounts during reinfection. The antibodies bind to the pathogen and kill it.