A 6-week-old infant received the first dose of oral polio vaccine (OPV) as part of the national immunisation schedule. The mother reports the infant developed flaccid paralysis of one limb 30 days later. What is the most likely diagnosis and mechanism?

• A Vaccine-associated paralytic poliomyelitis (VAPP) — reversion of OPV Sabin strain to neurovirulence ✓
• B Vaccine-derived poliovirus paralysis (cVDPV) — reversion of attenuated OPV to neurovirulence
• C Wild-type poliovirus infection from contact with unvaccinated sibling
• D Transverse myelitis as a non-specific post-viral immune-mediated event

Explanation

Vaccine-associated paralytic poliomyelitis (VAPP) is a rare but well-recognised complication of OPV occurring in the vaccine recipient (or close unvaccinated contacts). It results from reversion of the attenuated Sabin strain OPV poliovirus to a more neurovirulent phenotype during replication in the gut. The risk is approximately 1 in 3–4 million doses for recipients; higher risk with first dose and in immunocompromised individuals. Vaccine-derived poliovirus (VDPV) is caused by prolonged circulation of OPV-derived virus in under-immunised populations with sustained genetic drift. This single-vaccine-recipient case with first dose OPV is VAPP, not cVDPV.

Reference: Ghai Essential Pediatrics, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.