A Vaccine Vial Monitor (VVM) on a vial of DPT shows that the inner square has become darker than the outer circle. The correct action is:
- A Use the vaccine immediately as the darkening merely indicates heat exposure, not inactivation
- B Do NOT use the vaccine; discard it ✓
- C Send the vial to the cold chain laboratory for potency testing before use
- D Use if the vial is still within its expiry date
Explanation
The VVM is a heat-sensitive indicator placed on the vaccine vial to signal cumulative heat exposure. Reading: Stage 1 (initial) — square lighter than circle; Stage 2 — square matches circle (discard point reached, do not use); Stage 3 — square darker than circle (past discard point, DISCARD). When the inner square is darker than the outer circle, the vaccine has been exposed to excessive cumulative heat and must be discarded regardless of expiry date or cold storage appearance. Using it (options A, D) risks administering a sub-potent vaccine. Potency testing in the field (option C) is not operationally feasible.
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.