Combine the sugar, water, vanilla bean seeds, and scraped vanilla bean halves in a small saucepan over medium high heat. Stir to combine and bring to a simmer. Cook, stirring occasionally, until the sugar has dissolved. Remove from the heat. Stir in the vanilla extract and let the syrup cool. Pour into a jar and refrigerate until needed.
Notes
Feel free to substitute 2 additional teaspoons of vanilla extract for the vanilla bean, if you do not have vanilla beans on hand. It will work fine both ways. The syrup will be prettier with the flecks of vanilla floating in the syrup, but using the extract alone is definitely the more frugal option.