The Starbucks barista told me before that the Starbucks vanilla frappuccino doesn't contain any coffee so it doesn't contain any caffeine.
Although he did say that it could contain small amounts of caffeine due to the ingredients contained in the Starbucks vanilla frappuccino.
But he said that if it did contain caffeine it would be in really small amounts so if you're not supposed to have caffeine then it should not harm you at all.
When I drink a Starbucks vanilla frappuccino it never keeps me awake at night so I would say that it either doesn't contain any caffeine or if it does it's very little like the Starbucks Barista Said.
Although he may have been mistaken.
But my research online says that the Starbucks vanilla frappuccino doesn't contain any coffee nor caffeine.