system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
A herd immunity of over -% is considered necessary to prevent epidemic spread of diphtheria-
assistant
The correct answer is  <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>