Bacterial vaccine is a safe way to prevent dangerous bacterial disease, its treatment is very difficult after infection. So by taking the strains of a specific bacterial disease and attenuate it and inject it to individuals, there is an attenuated antigen entering the body, so the immune system will response by forming antibody for this antigen. Then the memory cells of the immune system will store information about this antigen. Then when the body is exposed to this antigen, but with a whole virulence factor there will be an immunity formed against this pathogen, so the infection can not be developed. So in this way we prevent a disease in a safe way, because these injected strains is virulent and can not cause infection.