Disease elimination is helped by-

Ans. is 'a' i.e., Herd immunity o If the herd immunity is sufficiently high, the occurrence of an epidemic is regarded as highly unlikely.o If that high level of immunity is maintained and stepped up, by an on-going immunization programme, to the point where the susceptible persons are reduced to a small proportion of the population, it may lead to elimination of the disease in due course.o This has been achieved in such diseases as diphtheria and polio.