Can you tell me how a vaccine provides immunity against infection. what problems are associated with the use of a?

Turn on immunity: Vaccines take a substance that mimics the shell of a virus or bacteria and introduces it into the body. That substance triggers the immune system to create antibodies.Those antibodies will capture and eliminate the wild germ if the patient is exposed at some future time. The vaccines undergo decades of development and constant surveillance. They are safe and effective when used as designed.