There are multiple studies going on in parallel. Some of them use a 10-day placebo, others compare 5-day and 10-day treatments. https://www.gilead.com/news-and-press/press-room/press-relea... https://www.nih.gov/news-events/news-releases/nih-clinical-t... https://www.thelancet.com/journals/lancet/article/PIIS0140-6...