Which of the following describes what a vaccine does?

A vaccine primarily functions by stimulating the immune system to produce immunity against specific pathogens, such as viruses or bacteria. When a vaccine is administered, it introduces a harmless component of the pathogen (like a protein or a piece of genetic material) or a weakened version of the pathogen itself. This prompts the immune system to recognize the invader and create an immune response. As a result, the body develops memory cells that allow it to recognize and fight off the actual pathogen if exposed in the future.

This immune response is crucial because it does not merely prevent current infections; instead, it prepares the immune system for potential future encounters with the pathogen. Thus, the statement that describes what a vaccine does most accurately emphasizes its role in stimulating the immune system to develop lasting immunity.

In contrast, the other choices do not accurately represent the function of vaccines. Vaccines do not boost energy levels, prevent all infections, or cure existing diseases. The nature of vaccines is preventive, focusing on building immunity rather than addressing an ongoing infection or condition.