A 18-month-old girl from an urban slum in Mumbai is brought to the immunization clinic by her mother. The child has received 3 doses of OPV (at birth, 6 weeks, and 10 weeks) but missed the booster dose at 16 months. The mother reports that the child has not had any recent illness. On examination, the child is alert and has normal muscle tone and power in all limbs. The immunization worker notes that a case of vaccine-derived poliovirus (VDPV) type 2 was recently confirmed in a neighbouring district. What is the most appropriate immediate action?

Explanation

## Clinical Context This is a case of an incompletely vaccinated child in an urban setting where VDPV type 2 has been detected. VDPV emerges when OPV coverage falls below critical thresholds, allowing the attenuated vaccine virus to circulate and accumulate mutations in under-immunized populations. ## High-Yield: VDPV and Polio Eradication Strategy **VDPV type 2 (VDPV2) is a known complication of OPV use in low-coverage areas**, but the solution is NOT to abandon OPV — rather, it is to: 1. **Increase OPV coverage urgently** through pulse polio campaigns 2. **Raise population immunity** to >95% to prevent VDPV circulation 3. **Complete vaccination** of all missed children 4. **Monitor through environmental surveillance** (sewage sampling) ## Key Point: VDPV Emergence and Response **VDPV emerges when:** - OPV coverage drops below 85–90% - Immunocompromised individuals shed vaccine virus for prolonged periods - Inadequate population immunity allows vaccine virus to circulate and mutate **VDPV is suppressed by:** - **Rapid increase in OPV coverage** (pulse polio campaigns) - **High population immunity** (>95%) - **NOT by switching to IPV** — IPV does not interrupt VDPV circulation ## Mnemonic: VDPV Management — **RAISE** - **R**aise OPV coverage immediately - **A**ctivate pulse polio campaigns - **I**ncrease surveillance (stool, sewage) - **S**upport immunization of all missed children - **E**nvironmental monitoring for poliovirus ## Clinical Pearl: Why OPV Booster + Campaign? In this scenario: - The child is **not sick** and has **normal neurology** — no contraindication to OPV - She is **incompletely vaccinated** and at risk - **VDPV detection** is a signal to **increase OPV coverage**, not reduce it - **Pulse polio campaigns** rapidly vaccinate all children in the district, raising herd immunity above the critical threshold (>95%) needed to suppress VDPV circulation - This is the **proven strategy** used in India's successful polio eradication efforts [cite:Park 26e Ch 28] ## Table: OPV vs. IPV in VDPV Context | Scenario | Vaccine | Rationale | |----------|---------|----------| | VDPV detected, low OPV coverage | OPV + pulse campaign | Rapid mucosal immunity, interrupts VDPV | | VDPV detected, high OPV coverage (>95%) | Switch to IPV | No VDPV risk, maintain immunity | | Polio-free region | IPV | Systemic immunity sufficient | | Endemic area, no VDPV | OPV | Standard eradication strategy | ## Warning: Common Misconception ~~Switching to IPV will prevent VDPV~~ — IPV does not induce mucosal immunity and cannot interrupt VDPV circulation in the community. VDPV is suppressed by **raising OPV coverage and population immunity**, not by abandoning OPV.