This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunization, Subject name: Pediatrics
[{'content': 'Vaccine with maximum efficacy \nSelect and explain. \nA. OPV, B. Measles, C. BCG, D. TT', 'role': 'user'}, {'content': "Answer: B \nExplanation: b. Measles(Ref: Nelson's 20/e p 1546, Ghai 8/e p 145; IAP guidebook of Immunization 2013-14, p 222-223)Seroconversion rates after measles vaccination are around 60% at the age of 6 months, 80-85% at the age of 9 months and beyond 95% at the age of 12-15 months.", 'role': 'assistant'}]