## Live Attenuated Vaccines and Cold Chain Requirements **Key Point:** MMR vaccine is a lyophilized (freeze-dried) live attenuated vaccine that is highly temperature-sensitive and must be reconstituted immediately before use. Once reconstituted with the provided diluent, it remains potent for only 30 minutes at room temperature (or 8 hours if refrigerated at 2–8°C). ### Cold Chain Characteristics of MMR | Feature | MMR Vaccine | |---------|-------------| | Type | Live attenuated | | Storage temperature | 2–8°C (frozen at −15°C or colder preferred) | | Stability after reconstitution | 30 min (room temp); 8 hrs (refrigerated) | | Diluent required | Yes (supplied) | | Discard after expiry | Mandatory | **High-Yield:** MMR is one of the most temperature-labile vaccines in the routine immunization schedule. Improper reconstitution or storage leads to vaccine failure and inadequate seroconversion. **Clinical Pearl:** In India's Universal Immunization Programme (UIP), MMR is given at 9 months and 15–18 months. Cold chain maintenance is critical to ensure vaccine efficacy, especially in resource-limited settings. ### Comparison with Other Vaccines - **OPV (Option A):** Live attenuated but more stable; can be stored at 2–8°C for months and does not require reconstitution. - **IPV (Option C):** Inactivated vaccine; more heat-stable than live vaccines; no reconstitution needed. - **Hepatitis B (Option D):** Inactivated vaccine; stable at 2–8°C; no special reconstitution requirements. **Mnemonic:** **LIARS** = Live vaccines need Immediate Reconstitution And Rapid use, Sensitive to temperature.
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