Mothers pass antibodies to their babies before birth, so they are born with protection from some diseases, but this protection is temporary. Immunization or vaccinations are given as a way to create immunity to or protection from some diseases. Vaccines stimulate the immune system to react as if there were an actual infection. It fends off the “infection” and remembers the germ, and later the germ if it enters the body later.
For more information on Immunizations, visit https://kidshealth.org/en/parents/vaccine.html.