This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
[{'content': 'Vaccine with highest efficacy- \nSelect and explain. \nA. Measles, B. DPT, C. Oral typhoid, D. Tetanus', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Three doses of DPT each of which is usually 0.5 ml should be considered optimal for primary immunization. It is associated with higher and more sustained levels of diphtheria and tetanus antitoxin and acceptable level of peussis protection i.e vaccine efficiency 70 percent. (refer pgno 162 park 23 rd edition)', 'role': 'assistant'}]