This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infectious disease, Subject name: Pediatrics
A 9-month-old infant is brought to you for immunization. The infant has previously received the first dose of OPV and DPT. What will you do? 
Select and explain. 
A. Repeat the first dose counting a fresh, B. Give the infant DT/polio, C. Give the infant second dose of DPT/OPV, D. Give the infant a booster dose of DPT/polio
D: Give the infant a booster dose of DPT/polio
Answer: D: Give the infant a booster dose of DPT/polio 
Explanation: A lapse in the schedule of immunization does not necessitate reinstitution of the total course. If the second or third dose of DPT or OPV was missed or delayed,there is no need of giving all the three doses of primary vaccination schedule. Reference:Ghai essential pediatrics 6th edition Page 191