A district health officer receives a report of a child with Vaccine Derived Poliovirus (VDPV) type 2. The child received bOPV (bivalent oral poliovirus vaccine) as per schedule. What is the MOST likely source of this VDPV2?
- A Reverted Sabin type 2 strain from a community contact who received trivalent OPV (tOPV) before the OPV2 switch ✓
- B Contamination of bOPV vials with wild type 2 poliovirus
- C Breakthrough from incomplete bOPV vaccination series
- D Type 2 IPV vaccine failure due to cold chain break
Explanation
India switched from tOPV (containing types 1, 2, 3) to bOPV (containing types 1 and 3 only) in April 2016 as part of the global OPV2 withdrawal. Simultaneously, a dose of IPV was introduced. Type 2 VDPV arises from mutation/recombination of Sabin type 2 vaccine strain — the source is community circulation of Sabin 2 virus from individuals who received tOPV before the switch (especially in settings with incomplete IPV coverage). Children now receive only bOPV + IPV; they have no type 2 OPV-derived mucosal immunity. VDPV2 can circulate in under-immunised communities from residual Sabin 2 spread. Wild type 2 poliovirus has been eradicated globally since 1999 (option B is implausible). bOPV contains no type 2 component, so option C is incorrect.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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