Question

The efficiency of cold chain system for oral polio vaccine, as monitored by the 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 of colour on the label of the bottle

Hint:

Think about what a VVM sticker physically does, not the vaccine liquid itself.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept.
The Vaccine Vial Monitor, or VVM, is a small heat sensitive label stuck on the vial or ampoule of oral polio vaccine. It tells health workers in the field whether the vaccine inside has been damaged by heat during transport and storage, without needing a lab test.

Step 2: Key Formula or Approach.
The VVM works on a simple rule. The inner square of the label is made of a heat sensitive material that darkens permanently as it takes in heat over time. As long as the inner square stays lighter than the outer reference ring, the vaccine can still be used. Once the inner square turns as dark as or darker than the ring, the vial must be discarded, even if the liquid looks and smells normal.

Step 3: Detailed Explanation.
Option (A), a change in the colour of the vaccine itself, does not happen. Oral polio vaccine looks the same whether it is potent or heat damaged, which is exactly why a separate monitor is needed.
Option (B), a temperature indicator of the system, describes a cold chain thermometer or freeze tag. That device only records the reading at one moment, not the total heat the vial has soaked up over its whole journey.
Option (C), a viral potency test, is a laboratory method that checks if the live virus in the vaccine still works. It needs lab equipment and cannot be read on the spot by a field worker.
Option (D), the change of colour on the label stuck on the bottle, matches how the VVM actually functions. The colour change adds up over time and cannot be reversed, so it reflects total heat exposure.

Step 4: Final Answer.
The cold chain efficiency for oral polio vaccine, as read from the VVM, depends on the change of colour on the label of the bottle.