Explain how a vaccine is used to strengthen the body's natural immune system against a virus?

A vaccine introduces a harmless part or a weakened form of a virus into the body, prompting the immune system to recognize it as a threat. This exposure stimulates the production of specific antibodies and activates immune cells, preparing the body to respond effectively if it encounters the actual virus in the future. By "training" the immune system in this way, vaccines enhance its ability to recognize and combat the virus more efficiently, thereby providing immunity.