This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Communicable diseases, Subject name: Social & Preventive Medicine
[{'content': 'Herd immunity is not impoant in \nSelect and explain. \nA. Tetanus, B. Peussis, C. Diphtheria, D. All', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The epidemics wave declines with an up-built of herd immunity after natural infection and if high-level immunity maintained with immunization disease eliminated, e.g. Polio, Diphtheria. It is neither possible nor necessary to achieve 100% herd immunity in a population to halt an epidemic or to control the disease. E.g. smallpox eradication. In the case of tetanus, it does not protect the individual. Epidemiology of Infectious Diseases. Ref: Park text book 24th edition.', 'role': 'assistant'}]