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

• A Use the vaccine immediately as it is at peak potency
• B Do NOT use the vaccine and discard it ✓
• C Store the vaccine at -20°C before further use
• D Return the vaccine to the district cold store for re-testing

Explanation

A VVM reading where the inner square is DARKER than the outer circle means the endpoint has been reached or exceeded — indicating the vaccine has been exposed to excessive heat for too long and has lost potency. The vaccine should NOT be used and must be discarded. The VVM reading point (inner square matches outer circle) is the discard point; beyond that (inner darker), discarding is mandatory. If the inner square is lighter than the outer circle, the vaccine can be used. The VVM is a cumulative heat indicator that detects temperature abuse.

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.