A Vaccine Vial Monitor (VVM) is placed on a vial of OPV. The inner square has become darker than the outer circle. The correct interpretation is:

• A The vaccine has been exposed to freeze damage
• B The vaccine is still usable provided the cold chain is maintained
• C The VVM shows Stage 2 — use if expiry date is valid
• D Discard Point has been reached; do NOT use the vaccine ✓

Explanation

VVM stages: Stage 1 (inner square lighter than outer circle — GOOD USE); Stage 2 (inner square same colour as outer circle — CAUTION, approaching end-point); Discard point (inner square darker than outer circle — DO NOT USE). When the inner square is darker than the outer circle, the cumulative heat exposure threshold has been exceeded, and the vaccine must be discarded. VVMs detect heat damage, not freeze damage; the shake test is used to detect freeze-damage in DPT, TT, Hep B, and DT vaccines.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.