Principle of vaccination is based on the property of ‘memory’ of immune system. In vaccination, a preparation of antigenic proteins of pathogens or inactivated/live but weakened pathogens is introduced into the body. The antigens generate primary immune response by producing antibodies along with forming memory B-cells and Tcells. When the vaccinated person is attacked by the same pathogens, second time/subsequent time the existing memory B-cells and T-cells recognise the antigen and overwhelm the invaders with massive production of lymphocytes and antibodies. Hepatitis B vaccine is produced from yeast.
