A 9-month-old female infant from Delhi is brought to the primary health centre for routine immunisation. The health worker notes that the vaccine refrigerator temperature has fluctuated between 2°C and 12°C over the past 24 hours due to a power outage. The vaccines currently in the refrigerator include: (1) Pentavalent vaccine (multi-dose vial, opened 1 week ago), (2) Measles vaccine (unopened, single-dose vial), (3) OPV (multi-dose vial, opened 2 weeks ago), and (4) Hepatitis B vaccine (unopened, multi-dose vial). Which vaccine(s) should be removed from the cold chain and discarded due to temperature excursion?

Question

Accepted Answer

B. Only Measles vaccine, because single-dose vials are more sensitive to temperature fluctuations. ## Temperature Excursion and Vaccine Stability

**Key Point:** Vaccine sensitivity to temperature excursion depends on **formulation** (lyophilized vs. liquid), NOT on whether the vial is opened or single-dose vs. multi-dose. Lyophilized (freeze-dried) vaccines are far more heat-sensitive than liquid vaccines.

### Cold Chain Basics (Park's Textbook of Preventive & Social Medicine)

The recommended storage temperature for most vaccines is **+2°C to +8°C**. In this vignette, the refrigerator reached **12°C** — a temperature excursion of 4°C above the upper safe limit for 24 hours.

### Vaccine-by-Vaccine Analysis

| Vaccine | Formulation | Status | Action After Excursion |
|---------|-------------|--------|------------------------|
| Pentavalent (DPT-HepB-Hib) | Liquid suspension | Multi-dose, opened 1 week ago | **Retain** — liquid vaccines are relatively heat-stable; also check VVM |
| **Measles** | **Lyophilized (freeze-dried)** | Unopened, single-dose | **Discard** — lyophilized vaccines are extremely heat-sensitive; even brief exposure >8°C degrades potency |
| OPV | Liquid (live attenuated) | Multi-dose, opened 2 weeks ago | **Retain** — liquid; also check VVM; already past 2-week open-vial policy but that is a separate issue |
| Hepatitis B | Liquid suspension | Unopened, multi-dose | **Retain** — liquid vaccine; stable up to 25°C for short periods |

**Why NOT option D (discard all)?** The WHO/UNICEF Vaccine Management Handbook and Park's PSM clearly distinguish between lyophilized and liquid vaccines. Liquid vaccines (OPV, Pentavalent, Hepatitis B) have greater thermostability and are NOT automatically discarded after a single excursion to 12°C, provided the Vaccine Vial Monitor (VVM) has not reached the discard point.

**Why NOT option A?** The rationale in option A is incorrect — it is the **lyophilized formulation**, not the "unopened" or "single-dose" status, that determines heat sensitivity. Hepatitis B is also unopened but is a liquid vaccine and can be retained.

**Why NOT option C?** Multi-dose vs. single-dose is irrelevant; formulation is the key determinant.

**High-Yield:** The correct answer is **Measles vaccine only** — because it is the only **lyophilized** vaccine among the four listed. Lyophilized vaccines (Measles, MMR, BCG, Varicella) must be discarded after any temperature excursion above 8°C.

**Clinical Pearl (Park's PSM, 25th edition):** After a temperature excursion, use the VVM status and shake test (for liquid vaccines) to guide retention decisions. For lyophilized vaccines, there is no field test — discard is mandatory after confirmed excursion above 8°C.

**Mnemonic: "LYOPHILIZED = FRAGILE"** — Freeze-dried vaccines (Measles, MMR, BCG, Varicella) are extremely sensitive to heat and must be discarded after any temperature excursion above 8°C, regardless of vial status.

Answer

A. Measles vaccine and Hepatitis B vaccine, because unopened vials cannot tolerate temperature excursions above 8°C

Answer

C. Pentavalent vaccine only, because multi-dose vials are more susceptible to temperature damage than single-dose vials

Answer

D. All four vaccines, because any temperature excursion above 8°C renders all vaccines unsafe

Explanation

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