(a) Who discovered 'vaccine for the first time' ? (b) Name two viral diseases which can be prevented by using vaccines. What is immunity?

(a) Edward Jenner discovered vaccine.
(b) Viral diseases prevented by vaccines - Hepatitis A, Polio, Chickenpox.
Immunity means the resistance of the body to a disease. It is due to the presence of antibodies in our body for the disease causing microorganisms known as antigens. When these antigens enter our body, antibodies are formed which prevent the disease.