Evaluation of the 2016 switch from tOPV to bOPV: Lessons learned and implications for an anticipated bOPV cessation

In 2016, Sabin poliovirus type 2 was withdrawn from trivalent oral poliovirus vaccine (OPV) (i.e., the switch), as a step toward global polio eradication. While the goal of the switch was to eliminate type-2 circulating vaccine-derived poliovirus (cVDPV2), in the eight years since there have been >3,300 children paralyzed (across 43 countries) (a 10-fold increase compared to pre-switch era). With plans underway for cessation of bivalent types 1 and 3 OPV (bOPV), it is critical to learn lessons from the failure of the switch. We conducted a formal evaluation of the switch, including quantitative and qualitative components (with stakeholder interviews) and an extensive peer-review process. The overarching reason for the switch failure was the inability to close out cVDPV2 outbreaks (due to suboptimal quality, inadequate scope and long delays of outbreak response vaccination), facilitated by leadership shortcomings (especially the inability to recognize the rapidly expanding outbreaks), and 10 key exacerbating factors. We propose criteria and recommendations for the anticipated bOPV withdrawal. The evaluation has influenced the planning for bOPV cessation, with more stringent requirements and adjusted timelines.