Combine water, sugar, ginger and pears in a large saucepan. Bring to a boil over medium-high heat, stirring occasionally. Strain out the solids and return the mixture to the pan.
Add the remaining pears, cider, lemon and allspice and heat over medium-high heat, stirring often, for 15 minutes.
Add cranberries and vanilla and reduce the heat to medium-low (the liquid should be simmering, not boiling). Let simmer for 10 minutes. Server in heat-safe mugs.