Immunization is the process whereby a person is made immune or resistant to an infectious disease, typically by the administration of a vaccine [1]. Vaccines stimulate the body’s own immune system to protect the person against subsequent infection or disease [1]. Infants, children, adolescents, teens and adults need different vaccinations, depending on their age, location, job, lifestyle, travel schedule, health conditions or previous vaccinations [2].

Source 1: http://www.who.int/topics/immunization/en/
Source 2: https://www.cdc.gov/vaccines/vpd/vaccines-diseases.html