Vodka is a highly distilled alcohol and should not contain sugar. Flavored vodkas, however, may contain some sugar as a component of their flavoring agent.
Generally, the sugar content of an alcoholic beverage is inversely proportionate to the amount of alcohol. Yeast, a type of fungus used in the fermentation process, metabolizes the sugars present in the brewing medium. The longer the fermentation process, the more sugar is converted into alcohol. Distillation, or the process of removing evaporated alcohol from the brewing medium, also ensures the beverage's purity. Heavier molecules, like sugar, cannot make the transition to a vapor and are left behind to continue their conversion to alcohol.