Pediatrics The efficiency of cold chain system for oral polio vaccine as monitored by Vaccine Vial Monitor (VVM) depends on: A Change in the colour of vaccine B Temperature indicator of the system C Viral potency test D Change in colour of monitor 💡 Explanation The efficiency of cold chain system for oral polio vaccine as monitored by Vaccine Vial Monitor (VVM) depends on: ✓ Correct Answer: D. Change in colour of monitor