1. Vaccination was discovered by a British doctor called Edward Jenner in the year 1776. Since then, this method has been modified and has become most popular for making people resistant to disease. 

2. In this process, the disease causing organism are cultured in the laboratory and are collected. They are killed by heat treatment. 

3. The dead micro-organisms are made into a suspension and injected into humans. The body reacts to these dead microorganisms as if they are alive and are produces antibodies. 

4. Next time when the same disease producing micro-organisms enter the body, these antibodies will react and kill them. 

5. Thus the person is not affected by the disease, even if he is exposed to the disease causing microorganisms. Vaccination also prevents the spread of epidemics. 

6. At present, vaccines are available for various diseases-Cholera, typhoid, diphtheria, whooping cough, polio, tuberculosis etc. Some of the vaccines if taken once, the immunity persists for life time, while in some cases the immunity will lasts only for limited amount of time.