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
Zero dose of polio vaccine in which is give 
Select and explain. 
A. Before giving DPT, B. At bih, C. When child is having diarrhoea, D. When child is having polio
B: At bih
Answer: B: At bih 
Explanation: the WHO programme on immunisation and the national immunisation programme in india recommend a primary course of 3 doses of OPV at one month intervals,commencing the first dose when infant is 6 weeks old.it is recommended that a dose of OPV (zero dose)is required to be given to all children delivered in health institutions before their discharge from hospital. ref:parks textbook ,22nd edition,pg no 187