https://techcrunch.com/2019/10/21/nielsen-says-it-can-now-measure-amazon-prime-video/

Nielsen announced this morning it will now be able to measure the viewing taking place on Amazon Prime Video, through its Subscription Video on Demand Content Ratings solution. This product, first launched two years ago, was originally focused on measuring Netflix’s viewing numbers with promises to add support for measuring Prime Video in 2018.

Though delayed by a year, that Prime Video measurement is now available.