The Vaccine Vial Monitor (VVM) on an OPV vial shows the inner square darker than the outer circle. The correct action is:

• A Use the vaccine if it has been stored correctly and the VVM just reached endpoint
• B Send the vial to district store for repeat cold chain verification
• C Use only for catch-up immunisation, not for children under 6 weeks
• D Discard the vaccine — the inner square being darker indicates heat damage ✓

Explanation

The VVM works by comparing the colour of the central square to the outer circle. When the central square is the SAME colour as or DARKER than the outer circle, the vaccine has reached its cumulative heat exposure endpoint and should be discarded regardless of expiry date. VVM Stage 4 (square darker than circle) = discard. Stage 1 (no colour change, clear square) = safe to use. Stage 2 (slight darkening but still lighter than circle) = use soon. This is a critical cold chain safety rule.

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.