A cold chain assistant suspects a shipment of DPT vials was accidentally frozen. He performs the shake test on a suspect vial alongside a control vial that was never frozen. After 30 minutes of standing, the suspect vial shows a thick layer of sediment while the control shows fine uniform dispersal. The correct interpretation is:
- A Suspect vial is normal, since DPT tolerates freezing
- B Suspect vial is damaged by freezing and must be discarded ✓
- C Both vials are usable, sedimentation is expected with adsorbed vaccines
- D Test must be repeated after warming both vials to body temperature
Correct answer: B. Suspect vial is damaged by freezing and must be discarded
Explanation
Freezing breaks the aluminium adjuvant emulsion of adsorbed vaccines like DPT, TT, Td, hepatitis B, pentavalent and PCV. On the shake test a frozen vial sediments rapidly as coarse particles within 15 minutes, whereas an intact vial stays cloudy with slow settling. Rapid sedimentation compared with the control means irreversible damage, so the batch is discarded. DPT is explicitly freeze-sensitive, so option A is wrong.
Reference: WHO Immunization in Practice: a practical guide for health staff, 2015 ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.