CBSE Class 9 Answered
The human body's natural defence against infection is called immunity. When we get an infection, our bodies produce chemicals called antibodies to fight it. After an infection we are usually immune to that virus or bacterium and the immunity may last for life. However, we can stimulate this immunity, without getting the full-blown disease or infection, by using immunisations, also called vaccinations. Immunisations are given by injection or by mouth. They work by introducing a very dilute version of the disease into the body, making it create antibodies, without actually causing the disease.
Diseases like polio, tetanus and diptheria can be prevented by immunisation.
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