In the cold chain, the vaccine vial monitor (VVM) on an OPV vial changes colour from a white inner square lighter than the outer circle to a dark inner square matching or darker than the outer circle. What does this indicate?

• A The vaccine has been exposed to excessive heat and should NOT be used ✓
• B The vaccine is optimally stored and safe to use
• C The vaccine has been frozen (freeze-indicator change)
• D The VVM indicates the vaccine has passed its expiry date

Explanation

The Vaccine Vial Monitor (VVM) is a heat-sensitive label that undergoes irreversible colour change upon cumulative heat exposure. The inner square of the VVM starts lighter than the outer circle (safe to use). When the inner square matches or becomes darker than the outer circle, it indicates excessive cumulative heat exposure — the vaccine should be discarded (Stage 3 or 4 depending on classification). VVMs are particularly important for OPV (oral polio vaccine) and other heat-sensitive vaccines. Freeze indicators (FreezeTag) are separate and detect freezing damage in freeze-sensitive vaccines (DTP, hepatitis B, influenza). The VVM does NOT indicate expiry date.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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Written and medically reviewed by the StethoPrep medical team.