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

Explanation

Vaccine has antibody-generating agents which may have killed germs or attenuated live germs or inactivated toxins having antigenicity and called Toxoid or readymade antibodies.
(a) Vaccination is based on the property of ..memory.. of the immune system.
(b) When a vaccine is injected, it generates the primary immune response of low intensity but also produces memory B-and T-cells. When the person is given the same vaccine for second time, the existing memory cells recognize the antigen and initiate a very quick secondary immune response of high intensity by producing large number of antibodies.
(c) Hepatitis-B vaccine has been produced from yeast by recombinant DNA technique.