A major clinical trial found that injections of ViiV Healthcare’s long-acting cabotegravir given every eight weeks as pre-exposure prophylaxis (PrEP) was even more effective at preventing HIV than daily Truvada pills.

The blinded, placebo-controlled trial included nearly 4,600 transgender women and cisgender men who have sex with men who were at risk of contracting HIV.

Participants in the trial were randomly assigned to receive either long-acting cabotegravir injected into the muscle by a health care worker every eight weeks or daily Truvada (tenofovir disoproxil fumarate/emtricitabine) pills as PrEP. Those in the cabotegravir arm received placebo pills to take daily, while those in the Truvada arm received placebo injections every eight weeks.

A planned independent review of the study revealed a clear indication that cabotegravir was highly effective at preventing HIV. What’s more, when comparing the HIV acquisition rates between the two study groups, the reviewers found that the long-acting PrEP regimen reduced the population-level rate by 66% more than the daily Truvada regimen.

Therefore, the placebo phase of the study was ended early. Everyone will be told which drug they’d been receiving, and everyone in the Truvada group will be offered cabotegravir.

The study’s findings do not necessarily mean that cabotegravir is more effective than Truvada when an individual takes the pills every day. Researchers estimate that taking Truvada daily lowers the risk of contracting HIV by more than 99% among men who have sex with men. Both regimens proved highly effective at preventing HIV in the study, and the difference may have been driven by somewhat compromised adherence in the daily Truvada group.

That said, the trial suggests that prescribing long-acting cabotegravir injections to a large group of people may be more effective at reducing the overall rate of HIV acquisition among them than prescribing daily Truvada to a similar large group.

“Each year, an estimated 1.7 million people are newly diagnosed with HIV” worldwide, says Myron S. Cohen, MD, the co–principal investigator of the trial and a professor at the University of North Carolina at Chapel Hill. “To lower that number, we believe more prevention options are needed in addition to currently available oral tablets for daily use.”