A moisture barrier is needed for hydroscopic materials that are in contact with possibly wet soil - namely concrete and aggregate surfaces. Another time a vapor barrier is needed is when the flooring will be on a surface which, due to condensation from temperature differentials, may wet the laminate.
Your wood floor is not going to bring moisture or condensate to the laminate, therefore a vapor barrier isn't necessary. Condensate can form or collect at the base of the walls, where they meet the floor.
I know that isn't a yes or no answer, but it'll help you decide an answer to your question based on your own needs, usage and local weather.