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': 'Which vaccine gives herd immunity- \nSelect and explain. \nA. OPV, B. Typhoid, C. Cholera, D. None', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. is \'a\' i.e., OPV o The vaccine progeny of OPV is excreted in the faeces and secondary spread occurs to household contacts and susceptible contacts in the community. o Non-immunized persons may therefore, be immunized. o Thus widspread "herd immunity"results, even if only approximately 66% of the community is immunized.', 'role': 'assistant'}]