A 28-year-old woman attends an immunization clinic in Delhi for routine vaccination. The nurse accidentally leaves the vial of oral polio vaccine (OPV) on the counter at room temperature (28°C) for 6 hours. The clinic supervisor is concerned about vaccine potency. Which investigation is most appropriate to assess the viability of the exposed vaccine before it is administered to patients?

Question

Accepted Answer

C. Viral culture in monkey kidney cells to assess infectivity and potency. ## Assessment of OPV Viability After Temperature Excursion

### Viral Culture in Monkey Kidney Cells — The Gold Standard for OPV Potency

**Key Point:** OPV is a **live attenuated viral vaccine**. Its potency is entirely dependent on the viability and infectivity of the live poliovirus strains. The definitive investigation to assess whether a live viral vaccine retains potency after a temperature excursion is **viral culture in monkey kidney cells**, which directly measures infectivity (TCID₅₀ or plaque-forming units).

**High-Yield:** WHO and standard virology references (Jawetz, Murray) specify that potency testing of live viral vaccines such as OPV is performed by inoculating susceptible cell lines (classically Vero cells or primary monkey kidney cells) and measuring cytopathic effect — this directly confirms whether viable, infectious virus is present.

### Why Viral Culture Is the Most Appropriate Investigation

1. **Direct measure of potency** — Infectivity assay (TCID₅₀) quantifies the number of viable viral particles capable of causing infection, which is the functional definition of vaccine potency for a live vaccine.
2. **Gold standard** — Regulatory agencies (WHO, CDSCO) require cell-culture–based infectivity assays for lot-release testing of OPV.
3. **Clinically decisive** — A positive culture with adequate TCID₅₀ confirms the vaccine is safe to administer; a reduced titer mandates discard.
4. **Specific to the question's concern** — The stem asks about *potency* after heat exposure; only a functional infectivity assay answers this directly.

### Why Other Options Are Incorrect

| Option | Why Incorrect |
|--------|--------------|
| **ELISA (antigen concentration)** | Measures antigen quantity, not viability; denatured (non-infectious) antigen can still give a positive ELISA — does not confirm potency of a live vaccine |
| **Shake test (thermal stability test)** | Designed to detect **freeze damage** (disrupted emulsion) in adjuvanted vaccines (e.g., DPT, Hep B); OPV is a liquid formulation with no oil-in-water emulsion — the shake test is **not applicable** to OPV |
| **RT-PCR for viral RNA** | Detects RNA integrity, not infectivity; heat-inactivated virus retains RNA that is detectable by PCR — a positive RT-PCR does NOT confirm the virus is still alive or potent |

**Clinical Pearl:** The shake test is specifically validated for **adjuvanted, adsorbed vaccines** (DPT, DT, TT, Hepatitis B) to detect freeze damage — it is **not** the recommended test for OPV. For OPV, the cold chain indicator (vaccine vial monitor, VVM) is the field tool, while viral culture is the laboratory gold standard for potency.

### Cold Chain Context

OPV is highly heat-sensitive. Exposure at 28°C for 6 hours may compromise potency, making a formal potency (infectivity) assay the appropriate investigation when viability is in question before administration.

**[cite: Jawetz, Melnick & Adelberg's Medical Microbiology 28e; WHO Technical Report Series — OPV Potency Testing; Murray's Medical Microbiology 9e]**

Answer

A. ELISA to measure antigen concentration in the vaccine vial

Answer

B. Thermal stability test (shake test) to assess physical integrity of the vaccine formulation

Answer

D. Reverse transcription-PCR (RT-PCR) to detect viral RNA integrity

Explanation

Practice similar questions