The primary purpose of a vaccine is to stimulate the body's immune system to recognize and fight specific pathogens, such as viruses or bacteria. Vaccines work by introducing a harmless component of the pathogen (like an inactivated or attenuated form) to the body, prompting an immune response. This response leads to the production of antibodies, which can recognize and combat the pathogen if the individual is exposed in the future. By creating immunity without causing the disease, vaccines play a crucial role in preventing infectious diseases and have significantly reduced the incidence of many illnesses globally.