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

This question checks whether you know how a Vaccine Vial Monitor actually works on an oral polio vaccine vial.

1. Change in the colour of vaccine: The liquid vaccine does not change colour when it goes bad from heat, so this option is ruled out straight away.
2. Temperature indicator of the system: A temperature indicator or freeze tag only shows the reading at one single point in time. It cannot add up the total heat exposure across the whole cold chain journey the way a VVM does.
3. Viral potency test: Checking viral potency needs a proper laboratory setup and cannot be read on the spot by a health worker simply looking at a vial.
4. Change of colour on the label of the bottle: The VVM sticker has an inner square that keeps darkening step by step as heat builds up over time. Once that square matches or goes past the shade of the outer reference ring, the vaccine is unfit for use. This is a field level, on the spot check that field workers rely on every day.

A VVM is a sticker, not a test done on the vaccine liquid, and it works through a permanent colour change once the cumulative heat exposure crosses a fixed limit.

So the cold chain efficiency for oral polio vaccine is judged from the change of colour on the label of the bottle.