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Vaccines are preparation of antigenic proteins of pathogen or inactivated/weakened pathogen that are administered to people to make them immune to a disease.
The body produce antibodies in response to the antigens of the vaccine, so body has an enhanced immune response when actual infection is there. The memory B-cells and T-cells produce in response to the vaccine destroys the pathogen on any future encounter. Thus vaccine actually makes the person immmune to the disease.