During cold chain monitoring, a vaccine vial monitor (VVM) on a polio OPV vial shows the inner square darker than the outer circle. A healthcare worker is about to use this vial. What is the correct action?

• A Use the vial immediately as the VVM indicates optimal cold chain has been maintained
• B Shake the vial vigorously and re-check the VVM reading after 30 minutes
• C Discard the vial — when the inner square matches or is darker than the outer circle, the vaccine has been heat-damaged and must not be used ✓
• D Use only if the vial has not passed its expiry date regardless of VVM status

Explanation

The Vaccine Vial Monitor (VVM) is a heat-sensitive label affixed to vaccine vials to track cumulative heat exposure. The inner square gradually darkens with heat exposure. The decision rules are: inner square lighter than outer circle = use; inner square the same as outer circle (VVM end-point) = do not use; inner square darker than outer circle = discard immediately. When the inner square darkens to match or exceed the outer circle, cumulative heat exposure has surpassed the threshold, indicating vaccine potency may be compromised. This is an absolute discard endpoint regardless of expiry date.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.