A 6-month-old infant in rural India is brought to the primary health centre for routine immunisation. The vaccine carrier has been exposed to ambient temperature (32°C) for 4 hours during transport from the district cold store. Which vaccine from the scheduled immunisation programme would be CONTRAINDICATED for use and must be discarded?

## Cold Chain Management and Vaccine Stability **Key Point:** Oral Polio Vaccine (OPV) is the most temperature-sensitive vaccine in the Indian immunisation schedule and has the strictest cold chain requirements. ### Temperature Sensitivity of Common Vaccines | Vaccine | Storage Temperature | Stability at Room Temp (25–32°C) | Stability at Elevated Temp (>32°C) | |---------|-------------------|----------------------------------|------------------------------------| | **OPV** | 2–8°C | 6 months | **Unstable; discard after 4 hours** | | DPT (liquid) | 2–8°C | 6 weeks | 3–4 weeks | | Hepatitis B | 2–8°C | 6 months | 3–4 months | | BCG | 2–8°C | 6 months | 3–4 months | **High-Yield:** OPV loses potency rapidly once removed from 2–8°C cold chain. Exposure to ambient temperature >32°C for >4 hours renders it non-viable and must be discarded per WHO/IAP guidelines. **Clinical Pearl:** The "Vaccine Vial Monitor" (VVM) on OPV changes colour irreversibly when exposed to heat, serving as a visual indicator of cold chain breach. If the VVM window turns dark, the vaccine is unsafe to use. **Mnemonic:** **OPV = Oral Polio = Overly Particular about temperature** — it is the most fragile vaccine in the cold chain. ### Why Other Vaccines Are More Stable - **DPT, Hepatitis B, BCG:** All are inactivated or lyophilised vaccines with greater thermal stability. They tolerate brief excursions to room temperature better than OPV. - DPT and Hepatitis B can remain at 25–32°C for weeks without significant loss of potency. - BCG (lyophilised) is extremely stable and can tolerate brief temperature excursions. **Tip:** In resource-limited settings, OPV vials should be opened only immediately before use and discarded if not used within 4 hours of opening, even if refrigerated.