Halve vanilla bean lengthwise. Scrape the seeds into a medium saucepan. Add the pod, 2 cups blueberries, sugar, lemon zest, lemon juice and salt. Bring to a boil. Reduce heat to a low simmer and cook for 10 minutes.
Add the remaining 2 cups blueberries and cook over low heat for 5 minutes more. Serve warm or room temperature.
To make ahead: Refrigerate for up to 1 week; freeze for up to 3 months.
59 calories;0 g fat(0 g sat); 4 g fiber; 15 g carbohydrates; 0 g protein; 0 mcg folate; 0 mg cholesterol; 9 g sugars; 3 g added sugars; 51 IU vitamin A; 4 mg vitamin C; 16 mg calcium; 1 mg iron; 17 mg sodium; 61 mg potassium