A 6-month-old infant from rural India is brought to the primary health centre for routine immunisation. The health worker is preparing vaccines from the cold chain storage. Which vaccine type is most commonly responsible for cold chain breakage and loss of potency in the Indian immunisation programme?

Explanation

## Most Common Cause of Cold Chain Breakage in India **Key Point:** Oral Polio Vaccine (OPV) is the most temperature-sensitive vaccine in the routine immunisation schedule and is the commonest cause of cold chain failure in India. ### Thermostability Profile of Common Vaccines | Vaccine | Storage Temperature | Stability | Cold Chain Sensitivity | |---------|-------------------|-----------|------------------------| | OPV | 2–8°C | Highly unstable; loses potency rapidly above 8°C | **Highest** | | IPV | 2–8°C | More stable than OPV; can tolerate brief excursions | Moderate | | DPT | 2–8°C | Stable; tolerates temperature excursions better | Lower | | Measles | 2–8°C | Relatively stable; freeze-dried formulation | Lower | **High-Yield:** OPV must be stored at 2–8°C and loses potency irreversibly if exposed to temperatures above 8°C for even brief periods. Once thawed, OPV cannot be refrozen. ### Why OPV is Most Vulnerable 1. **Liquid formulation** — OPV is a liquid vaccine; freeze-dried vaccines (e.g. measles) are inherently more stable. 2. **Narrow temperature window** — Any excursion above 8°C causes loss of potency without visible change. 3. **No colour indicator in older formulations** — Vaccine Vial Monitors (VVM) now help, but OPV remains the highest-risk vaccine. 4. **High volume in immunisation schedule** — OPV is given at multiple time points (birth, 6 weeks, 10 weeks, 14 weeks, booster), increasing exposure risk. **Clinical Pearl:** In resource-limited settings, OPV cold chain failure is a major reason for vaccine-preventable disease outbreaks. Proper cold chain management (ice-lined refrigerators, vaccine vial monitors, avoiding door-opening) is critical. **Mnemonic:** **OPV = Often Perishes in Vehicles** — emphasises its extreme temperature sensitivity during transport and storage.