Only 7% children in the world’s poorest countries receive all 11 WHO recommended vaccines. Despite impressive progress on global immunisation coverage rates, too many children are still being left behind. Polio transition poses a unique opportunity to reinforce immunisation systems and turn a situation with great risk into one that leaves a positive legacy on child and global health. It is an opportunity that cannot be missed. The WHO Strategic Action Plan (the Plan) must set out how the WHO will take this opportunity and use its coordinating power to create ambitious change. In this briefing, we lay out our recommendations for how the Plan could be improved.