Mix pectin with 1/4 cup of the sugar; stir into berries. Halve vanilla bean lengthwise and scrape out seeds; stir seeds and pod into berries. Bring to full rolling boil over high heat, stirring constantly with a wooden spoon. Stir in remaining sugar and return to full rolling boil; boil hard, stirring constantly, for 1 minute. Remove from heat. Stir, skimming off foam, for 5 minutes. Discard vanilla pod.