Why vaccine is a protein that acts against a specific antigen?

A vaccine contains a harmless component or a weakened form of a specific pathogen, often a protein, that stimulates the immune system to recognize and respond to that pathogen. When introduced into the body, the vaccine prompts the immune system to produce antibodies and memory cells specific to the antigen, which is a molecule that triggers an immune response. This preparation allows the body to mount a faster and more effective defense if exposed to the actual pathogen in the future. Thus, vaccines help prevent diseases by training the immune system to recognize and combat specific antigens.