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
Which vaccine gives herd immunity- 
Select and explain. 
A. OPV, B. Typhoid, C. Cholera, D. None
A: OPV
Answer: A: OPV 
Explanation: 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.