For the simple syrup: Combine the sugar, vanilla bean and 2 cups water in a saucepan over medium heat. Cook, stirring, until the sugar melts. Remove from the heat and let cool. Cover and refrigerate for up to 2 weeks.
For the martini: In a cocktail shaker with ice, add the blood orange juice, vodka and 2 ounces of the simple syrup. Shake, then strain into a martini glass. Garnish with the orange zest.