Co-Administration of Novel Oral Polio Vaccine Type 2 and Bivalent Oral Polio Vaccine: Current Evidence, Challenges, and Implications for the Polio Eradication Endgame.

Global polio eradication is challenged by persistent wild poliovirus type 1 (WPV1) transmission and outbreaks of circulating vaccine-derived poliovirus type 2 (cVDPV2). The 2016 global withdrawal of the type 2 component from trivalent oral poliovirus vaccine (tOPV) created population immunity gaps, facilitating cVDPV2 emergence in areas with low routine coverage. We conducted a narrative review synthesizing biological, immunological, clinical, epidemiological, and operational evidence on co-administration of novel oral poliovirus vaccine type 2 (nOPV2) with bivalent OPV (bOPV) as a strategy to rapidly expand population immunity during multi-serotype outbreaks. Co-administration provides potential logistical and equity advantages. Emerging randomized trial data, however, reveal significant immunological interference that can reduce type 2 immune responses. The effectiveness of this strategy is therefore context-dependent, with operational feasibility and coverage levels critically influencing outcomes. Co-administration of nOPV2 and bOPV should be applied as a context-specific tactical measure rather than a universal policy. Sustained high vaccination coverage and robust surveillance remain central to achieving global polio eradication.