How vaccines work?

A vaccine is a special kind of preparation (or medicine) which provides immunity against a particular disease.

A vaccine works as follows:

A vaccine contains the dead or weakened but alive micro-organisms of a disease. When the vaccine containing dead or alive micro-organisms is introduced into the body of a healthy person orally ( by mouth) or by injection, the body of that person responds by producing some substances called antibodies in its blood. These antibodies kill the ‘alive’ disease-causing micro-organisms present in the vaccine. Some of the antibodies remain in the blood of the person for a very long time and fight against the same micro-organism and kill them if they happen to enter the body naturally later. So, due to the presence of antibodies in the blood, a person remains protected from that particular disease. Thus, a vaccine develops the immunity from a disease.