This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
[{'content': 'Herd immunity is not useful in - \nSelect and explain. \nA. Diphtheria, B. Polio, C. Measles, D. Tetanus', 'role': 'user'}, {'content': "Answer: D \nExplanation: Herd immunity has been achieved in diphtheria and poliomyelitis Small pox-herd immunity has not played a crucial role in its eradication. Tetanus- herd immunity doesn't protect the individuals ( refer pgno:103 park 23 rd edition)", 'role': 'assistant'}]