Under India's Universal Immunisation Programme, the Vaccine Vial Monitor (VVM) helps healthcare workers make field decisions. A VVM where the inner square is DARKER than the outer circle should be interpreted as:

• A Vaccine is within usable life — use before expiry
• B Vaccine requires refrigeration before use
• C Cold chain breach has occurred but vaccine may still be used
• D Vaccine has been irreversibly heat-damaged — discard the vial ✓

Explanation

The VVM is a time-temperature indicator attached to vaccine vials. When the inner square becomes darker than or equal to the outer circle (Stage 3 or 4), the vaccine must be discarded regardless of expiry date. The discolouration indicates cumulative heat exposure has reduced vaccine potency below acceptable levels. This is an irreversible reaction reflecting total heat damage. Health workers should use the principle: 'if in doubt, throw it out' when inner square reaches or exceeds outer circle colour.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.