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
9th month immunization given is 
Select and explain. 
A. Measles, B. DPT, C. BCG, D. All
A: Measles
Answer: A: Measles 
Explanation: The principal problem of measles immunization is timing; immunization before the age of 9 months runs the risk of the vaccine being rendered ineffective by the natural antibodies acquired through the mother. Immunization later than 9 months means a significant propoion of children will contract measles in the interval between the wearing of natural protection and the introduction of the vaccine. (refer pgno:149 park 23 rd edition)