A vaccine is introduced into a person's body to stimulate the body to produce antibodies. Vaccines contain weakened or dead pathogens that cannot cause disease, but can still trigger an immune response in the body. This means that when the person is exposed to the actual pathogen, their immune system will recognize it and quickly produce the necessary antibodies to fight the infection. By stimulating the body to produce antibodies in advance, vaccines can help prevent or reduce the severity of certain diseases.