U.S. health officials on Thursday announced they will shift the focus of a clinical trial in Botswana aimed at testing pre-exposure prophylaxis (PrEP) – the strategy that “a daily low dose of the drugs, which interfere with the ability of the virus to replicate, could also lower the risk of infection” – after researchers discovered they would be unable to determine the efficacy of Truvada, the medicine used in the trial, Reuters reports.

“Originally, the trial involving 1,200 people was trying to see if people could prevent infection with the AIDS virus if they took a daily pill that combined two HIV drugs,” the news service writes. “Other, similar trials are under way in the United States, South Africa, Thailand, Brazil, Peru, Kenya, Uganda and elsewhere,” Reuters writes.

“While the trial met its original enrollment goals, this study will not be able to determine efficacy given much lower than anticipated HIV incidence in the study population (likely due to declining HIV rates in Botswana generally, and to extensive HIV prevention services provided to all participants), and challenges in retaining participants in this highly mobile population of young adults,” the CDC said in a statement. “The trial, however, will provide critical information on safety and adherence to help guide potential implementation planning should PrEP prove effective in other trials,” the CDC said (Fox, 12/17).