The third current major trial to examine a promising HIV vaccine candidate is launching in late 2019, enrolling cisgender men and transgender individuals who have sex with men or trans people. The Phase III, placebo-controlled efficacy study, called Mosaico, will run out of approximately 55 clinical research sites in the United States, Mexico, South America and Europe. 

Mosaico will enroll 3,800 HIV-negative 18- to 60-year-old people who are in good health and at risk of acquiring the virus. They can’t be taking pre-exposure prophylaxis (PrEP) upon enrolling but may start PrEP during the trial. Over the course of a year, those randomized to the active vaccine group will receive four doses of a vaccine candidate, known as Ad26.Mos4.HIV, that recently drove a strong immune response in earlier trials. The participants will be followed for 18 months. The study should wrap up during the first half of 2023.