What is immunization? Explain its mechanism.

Immunization, or immunisation, is the process by which an individual's immune system becomes fortified against an agent (known as the immunogen). When this system is exposed to molecules that are foreign to the body, called non-self, it will orchestrate an immune response, and it will also develop the ability to quickly respond to a subsequent encounter because of immunological memory. This is a function of the adaptive immune system. Therefore, by exposing an animal to an immunogen in a controlled way, its body can learn to protect itself: this is called active immunization Immunisation protects children (and adults) against harmful infections before they come into contact with them in the community. Immunisation uses the body’s natural defence mechanism - the immune response - to build resistance to specific infections. Nine diseases can be prevented by routine childhood immunisation - diphtheria, tetanus, whooping cough, poliomyelitis (polio), measles, mumps, rubella, Haemophilus influenzae type b (Hib) and hepatitis B. All of these diseases can cause serious complications and sometimes death. Immunisation is given as an injection or, in the case of polio vaccine, taken as drops by mouth. Immunisation helps children stay healthy by preventing serious infections