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: Surgery
[{'content': 'In which case pneumococcal vaccine is most effective \nSelect and explain. \nA. When given preoperatively, B. When given post operatively, C. Against all strains of bacteria, D. Against gram negative bacteria', 'role': 'user'}, {'content': 'Answer: A \nExplanation: • When elective splenectomy is planned, vaccination against encapsulated bacteria should be given at least 2 weeks before surgery.\n• If spleen is removed in emergency, vaccination should be given as soon as possible following surgery.', 'role': 'assistant'}]