Description: Immunization helps the body’s immune system develop protection against some infectious diseases. Discover how vaccines produce immunity to a disease by helping the immune system learn to recognize and fight the germ that causes the disease. Explore the links to MedlinePlus health topic pages and ClinicalTrials.gov for trusted information about immunization and vaccine research.Immunization helps the body’s immune system develop protection against some infectious diseases. Discover how vaccines produce immunity to a disease by helping the immune system learn to recognize and fight the germ that causes the disease. Explore the links to MedlinePlus health topic pages and ClinicalTrials.gov for trusted information about immunization and vaccine research.