A herd immunity of over -% is considered necessary to prevent epidemic spread of diphtheria-: (A) 50%, (B) 55%, (C) 60%, (D) 70%
Answer is D. <p> A herd immunity of over 70% is considered necessary to prevent epidemic spread of diphtheria. Park&;s textbook of preventive and social medicine,K.Park,22nd edition,page no:151 <\p>