This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
[{'content': 'Typhoid revaccination is recommended every ... years in endemic area- \nSelect and explain. \nA. 1, B. 3, C. 5, D. 10', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., 3 o To maintain protection, revaccination is recommended every 3 years.", 'role': 'assistant'}]