## Cold Chain Integrity and Vaccine Viability **Key Point:** Live attenuated vaccines (LAV) such as MMR are highly sensitive to temperature fluctuations. Freezing and thawing cycles cause ice crystal formation that damages the viral envelope and reduces potency below acceptable levels. ### Cold Chain Requirements for MMR | Parameter | Requirement | Rationale | |-----------|-------------|----------| | Storage temperature | 2–8°C (refrigerated) | Prevents degradation of live virus | | Freeze-thaw cycles | Maximum 1 (some protocols allow 0) | Each cycle reduces viability | | Exposure to room temperature | <4 hours cumulative | Accelerates viral inactivation | | Once reconstituted | Use within 4 hours | Potency loss after reconstitution | **High-Yield:** The WHO and Indian immunization guidelines mandate **discard of any LAV that has undergone unplanned freezing or multiple thaw cycles**, regardless of appearance. The vaccine may appear normal but potency is compromised, leading to vaccine failure and false sense of immunity. **Clinical Pearl:** In this case, the vaccine underwent **two freeze-thaw cycles** (initial freezing, thaw due to malfunction, refreeze). This exceeds acceptable limits. Administering a non-potent vaccine exposes the patient to injection risk without conferring protection—particularly problematic in a woman planning pregnancy, who requires confirmed rubella immunity. ### Correct Action Discard the vial and obtain a new one from a properly maintained cold chain. Document the incident in the vaccine register and cold chain log. [cite:Park 26e Ch 6]
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