The Vaccine Vial Monitor (VVM) on a vial of OPV shows the inner square darker than the outer circle. This indicates:
- A The vaccine has been exposed to excessive heat and should NOT be used
- B The vaccine has been frozen and is safe to use
- C The vaccine has reached its discard point — the inner square matches or is darker than the outer circle ✓
- D The VVM reading is invalid and the vaccine should be used based on expiry date only
Correct answer: C. The vaccine has reached its discard point — the inner square matches or is darker than the outer circle
Explanation
The VVM changes colour progressively with cumulative heat exposure. When the inner square becomes as dark as or darker than the outer circle, the vaccine has reached its discard point and must NOT be used regardless of the expiry date. The Open Vial Policy applies to heat-stable vaccines; OPV is heat-sensitive. VVM stage 1 (square lighter than circle) = use; stage 2 (square same as circle) = discard; stage 3/4 (square darker) = discard.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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Written and medically reviewed by the StethoPrep medical team.