What is the basic principle of vaccination?How do vaccines prevent microbial infections?Name the organism from which hepatitis B vaccine is produced.

Explanation

The principle of vaccination is based on the property of .memory.of the immune system .In vaccination,a preparation of antigenic weakened pathogens is introduced into the body.The antigens generate the primary immune response by producing antibodies.The vaccines also generate the memory B-cells and T-cells.When the vaccinated person is attacked by the same pathogens.the existing memory B-cells or T-cells recognises the antigen quickly and overhelm the invaders with massive production of lymphocytes and antibodies.Hepatitis B vaccine is produced from yeast.