Under India's Universal Immunization Programme (UIP), the Vaccine Vial Monitor (VVM) changes colour from light to dark. A VVM in Stage 2 (inner square lighter than outer circle) indicates:

• A Vaccine has been exposed to excessive heat; discard immediately
• B Vaccine can be used but should be prioritized for use first ✓
• C Vaccine has crossed the discard point; do not use
• D Vaccine has been stored below 0°C (frozen); do not use

Explanation

VVM stages: Stage 1 — inner square lighter than outer circle (usable, good cold chain); Stage 2 — inner square matches outer circle (use first, approaching end-point); Stage 3 — inner square darker than outer circle (do not use, discard point reached); Stage 4 — square completely dark (beyond discard point). Stage 2 signals that the vaccine has experienced cumulative heat exposure approaching the endpoint; it remains usable but should be prioritized before vaccines with lighter VVMs. Freezing damage is indicated separately by shake test, not VVM.

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

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Written and medically reviewed by the StethoPrep medical team.