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
After reconstitution, the vaccine must be stored in the dark at 2-8 degree C and used within: September 2004 
Select and explain. 
A. 1 hour, B. 2 hours, C. 3 hours, D. 6 hours
D: 6 hours
Answer: D: 6 hours 
Explanation: Ans. D i.e. 6 hour Reconstituted measles vaccine loses about 50% of its potency after 1 hour at 20 degree C; it loses almost all potency after 1 hour at 37 degree C.