Does laminate flooring need an independent vapor barrier on concrete?
Lots of slabs are covered in carpet without any problem. It depends on your specific slab. To know you need to test the slab. Take a trash bag tape it down to the floor. In 24 hours pull it up. If the floor looks damp or there is moisture on the bag a barrier will be needed if it is dry no barrier is needed. I have epoxy painted to seal damp floors made a huge difference in the humidity. Even though you have underlayment on your flooring it is segmented, moisture under there is not desirable. If dry with the bag test use the bag for trash and start your floor. If wet decide on the best path forward and use your bag for some trash (don’t waste the bag just because it has some tape on the outside. Added since some don’t understand: 
Many slabs have a vapor barrier under them, so if your plastic test comes up dry no additional barrier may be needed. I mentioned carpet because it holds moisture but grows mold and mildew faster than laminate and if a slab can handle carpet it can handle laminate, the plastic test is how to know if it is wet / dry at any age.