An antiviral pill proved 100 percent effective in preventing new cases of HIV, according to a new Kaiser Permanente study.

Truvada was administered to 657 sexually-active people over 32 months – and there were no new cases of HIV reported, according to the study, published in the journal Clinical Infectious Diseases this month.

“Our study is the first to extend the understanding of the use of PrEP (pre-exposure prophylaxis) in a real-world setting and suggests that the treatment may prevent new HIV infections even in a high-risk setting,” said Jonathan Volk, physician and epidemiologist at Kaiser Permanente San Francisco Medical Center, and the lead author.

Ninety-nine percent of the subjects were men who have sex with men, according to the study. They were sexually active: within 12 months of the initiation of the Truvada regimen, 50 percent of the patients had contracted at least one kind of sexually-transmitted infection, like rectal infections, chlamydia, gonorrhea and syphilis.

But none contracted HIV.

A subset of the group reported not changing their number of sex partners over the time of treatment.

However, the researchers could not be sure if the antiviral treatments encouraged risky behaviors.

“Without a control group, we don’t know if these STI rates were higher than what we would have seen without PrEP,” said Julia Marcus, postdoctoral fellow at the Kaiser Permanente Division of Research, and a co-author. “Ongoing screening and treatments for STIs, including hepatitis C, are an essential component of a PrEP treatment program.”

Truvada was approved by the FDA in in July 2012 for daily oral use.

The results could even prove to be a breakthrough, according to an editorial that accompanied the study, written by staff from the University of California at San Francisco and the San Francisco AIDS Foundation.

“Given historical devastation wrought by HIV/AIDS within the city of San Francisco and elsewhere, this is tremendously good news,” they wrote. “The data published by Volk and colleagues demonstrates meaningful progress towards the goal of halting new infections.”

However, additional attention to growing rates of other STIs is necessary, they added.

“It is time for a vigorous conversation about sexually-transmitted infections, too long eclipsed by fear of HIV infection,” they added. “While HIV testing and trends are frequently in the news, notice of STI trends remain unnoticed in technical reports… Feeling safer from HIV infection while using PrEP creates spaces for a more robust discussion of STIs.”

Another potentially promising study was published last week in the journal Cell. Scientists from the California Institute of Technology have honed in on a particular antibody that naturally occurs in some patients who are naturally able to fend off HIV – and the researchers said it could prove to be a route to eradicate the infection.