Measles should not be used if it has been more than……..hours after reconstitution.

Correct option is B

Sol. According to WHO guidelines and India’s Universal Immunization Programme (UIP), once the measles vaccine is reconstituted, it must be used within 2 hours. After this, it should be discarded to avoid contamination and loss of vaccine potency.
Explanation of each option:
· (a) 1 hr – Although using within 1 hour is safe, the upper safety limit is 2 hours, so this is more restrictive than required.
· (b) 2 hrs – Correct answer. The vaccine remains safe and effective up to 2 hours post-reconstitution; beyond this, it must be discarded.
· (c) 3 hrs – Not acceptable. After 2 hours, vaccine potency drops and the risk of microbial contamination increases.
· (d) 4 hrs – This is beyond safe limits and can result in ineffective immunization or adverse reactions due to contamination.