What is the general purpose of immunization as a health-promotion measure?

Immunization is a primary prevention measure that works by stimulating the body's immune system to develop protection (immunity) against specific diseases before the person is exposed, thereby preventing the illness or reducing its severity. Vaccines do not treat existing infections, diagnose disease, or replace other health care. Immunization also contributes to community (herd) protection when enough people are vaccinated. Understanding the preventive purpose of immunization is a standard health-promotion concept. (This is a general principle; specific vaccine schedules and recommendations change over time and must be verified against current CDC/authoritative guidance and NCLEX prep materials.)