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: Skin
[{'content': 'What is the ideal time for staing post-exposure prophylaxis with acyclovir in a person exposed to varicella? \nSelect and explain. \nA. Immediately after exposure, B. 3rd day, C. 7-9 th day, D. 10-14 th day', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Antiviral therapy for prophylaxis against varicella should be staed 7 days after the intense exposure, using acyclovir. Ref: Harrisons Principles of Internal Medicine, 18th edition, Page: 1466', 'role': 'assistant'}]