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