a) The principle of vaccination is to produce immunity against a disease. Explain.
b) "Abnormally large number of WBC's in the blood is usually an indication of some infection in our body." Comment on the statement. [4 MARKS]

Each Part: 2 Marks

a) The aim of vaccination is to provide sufficient antigenic material to stimulate the body's immune system without causing the disease. If the number of hosts can be reduced to a low enough level, there may not be enough left to sustain the organism, which should then become extinct. This has happened with smallpox and it is hoped to come about with diseases such as polio.

b) If any microbe enters the body systems, the white blood cells (phagocytes) squeeze out of the walls of the blood capillaries by diapedesis and engulf the bacteria or the germs and destroy them (phagocytosis). For example, pus in a wound is a mixture of destroyed germs, killed WBC's and damaged tissue cells. Therefore, abnormally large number of WBC's in the blood is usually an indication of some infection in our body.