The Vaccine Vial Monitor (VVM) on a vial of oral poliovirus vaccine shows that the inner square is DARKER than the outer circle. The vial has not expired. What action should be taken?
- A Use the vaccine immediately as heat damage is not yet confirmed
- B Discard the vial — the VVM indicates the vaccine has been irreversibly heat-damaged beyond the safe threshold ✓
- C Send the vial to the district cold chain officer for retesting
- D Store the vial at −20°C to reverse the heat damage
Correct answer: B. Discard the vial — the VVM indicates the vaccine has been irreversibly heat-damaged beyond the safe threshold
Explanation
On a VVM, as cumulative heat exposure increases, the inner square progressively darkens. When the inner square is darker than (or the same colour as) the outer circle, the vaccine has exceeded its heat exposure limit (Endpoint) and must be discarded regardless of expiry date. VVMs do not recover — the colour change is irreversible. The four VVM reading points are: A (use), B (use), C (do not use if inner matches outer), D (discard — square darker than circle).
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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Written and medically reviewed by the StethoPrep medical team.