Question

Under polio prevention programme, infants in India were given polio vaccines on a large scale at regular intervals to eradicate polio from the country.

(a) What is a vaccine? Explain how does it impart immunity to the child against the disease.
(b) With the help of an example each, differentiate between active and passive immunity.

Answer 1

(a) A vaccine is a preparation containing a killed or attenuated pathogen or substances that mimic the disease-causing pathogen.

It imparts immunity to the child in following way:

• The inactivated pathogens in the vaccine, when introduced in the body, produce a primary immune response and antibodies are produced against the pathogen.

• Memory B and T cells are produced.

• Now, when the pathogen again attacks the person, memory B and T cells generate a massive immune response (secondary response) and the pathogen is killed

(b)

Active Immunity	Passive immunity
Body’s own cells produce antibodies in response to an infection.	Antibodies from another person or animal are injected into the afflicted person.
Person’s own immune response has to get activated and produce antibodies. Thus, it requires time for immunity development.	Ready-made antibodies are injected into the afflicted person and, thus, immunity develops immediately.
It is harmless.	It may cause reactions.
It provides long-lasting protection.	Its effects are short-lived.
Example: Production of antibodies by the body against diseases such as chicken pox	Example: Injection of horse serum antibodies for treating diseases such as tetanus