GlaxoSmithKline said on Tuesday its HIV unit ViiV Healthcare had started a large study to test an experimental long-acting injection for preventing the virus that causes AIDS.
Reuters reported last month that the pre-exposure prophylaxis (PrEP) study with cabotegravir was about to start.
The Phase III study aims to enrol 4,500 men who have sex with men, and transgender women who have sex with men, at more than 40 sites in North and South America, Asia and Africa. A second study involving young women is due to start in 2017.
The trial comes hard on the heels of news that GSK's new two-drug HIV tablet therapy successfully controlled HIV in two late-stage trials.