THURSDAY, Sept. 12, 2024 (HealthDay News) -- It could be a real breakthrough for people at risk for HIV infection: A shot given every six months that reduces their risk by a whopping 96%.

That's according to new trial results released Thursday by Gilead Sciences, which is repurposing its HIV treatment, the antiviral lenacapavir, as a twice-yearly preventive shot.

There's a catch, however: Given as either a pill or injection and currently branded as Sunlenca, lenacapavir as treatment for HIV infection is pricey, costing $3,450 per month or over $41,000 per year, NBC News reported.

Its price tag as a twice-yearly preventive injection -- pre-exposure prophylaxis, or PrEP -- has not yet been released by Gilead.

That has patient advocates worried.

“While lenacapavir is a valuable addition to our toolkit, for it to reach its full potential, it must be made accessible to those who stand to benefit the most from its effectiveness," Dr. Boghuma Titanji, an infectious disease specialist at Emory University, told NBC News.

The new trial involved a group of more than 3,200 individuals over the age of 15, mostly men who have sex with men. Participants were living in Argentina, Brazil, Mexico, Peru, South Africa, Thailand and the United States.

Beginning in 2021, all were randomly selected to take either the twice-yearly lenacapavir injection for PrEP or a once-daily Truvada pill, a longstanding form of PrEP.

No placebo group was included since leaving patients with no protection against HIV would be unethical.

The result: "99.9% of participants did not acquire HIV infection in the lenacapavir group, with 2 incident cases among 2,180 participants," Gilead said in a news release.

That beat Truvada's performance: There were nine cases of HIV infection among 1,087 people in the group taking the daily pill.

Relative to Truvada, twice-yearly lenacapavir reduced the odds for HIV infection by 96%, the researchers reported.

No safety concerns for those taking the drug were reported.

The performance of the Gilead drug was so impressive that the trial was halted early so that everyone could avail themselves of the treatment, the company said.

The new findings follow those of another clinical trial of twice-yearly lenacapavir, with similarly impressive results. That trial was conducted among at-risk women living in sub-Saharan Africa and was also ended early, after the Gilead regimen showed 100% effectiveness in preventing infection.

Gilead's CEO Daniel O'Day has high hopes for injected lenacapavir's potential, and the company plans to submit the drug for U.S. Food and Drug Administration approval by the end of 2024.

"With such remarkable outcomes across two phase 3 studies, lenacapavir has demonstrated the potential to transform the prevention of HIV and help to end the epidemic,” he said in the company news release.

“Now that we have a comprehensive dataset across multiple study populations, Gilead will work urgently with regulatory, government, public health and community partners to ensure that, if approved, we can deliver twice-yearly lenacapavir for PrEP worldwide, for all those who want or need PrEP," he added.

Besides its effectiveness in stopping the virus that causes AIDS, the new regimen's convenience is a huge plus.

“The difficulty some people can experience with taking an oral pill every day, including challenges with adherence and stigma, have hindered uptake and persistence of the standard of care for too long, thus blunting PrEP’s impact on HIV prevention,” said the trial's principal investigator, Dr. Onyema Ogbuagu.

The "potential benefits of a twice-yearly injection ... adds significantly to our arsenal of tools to move us closer to achieving an AIDS-free generation," he said in the Gilead news release. Ogbuagu is an associate professor of medicine at the Yale School of Medicine.

Experts in HIV/AIDS who weren't involved in the trials were optimistic about the drug's potential.

Speaking with NBC News, Jennifer Kates, director of global health and HIV policy at the nonpartisan health nonprofit KFF, called the new findings "nothing short of amazing."

But she added that breakthrough medicines have rocked the world of HIV prevention before -- only to lead to disappointment as cost limited access.

The effectiveness of twice-yearly lenacapavir "raises the stakes on the importance of getting this new tool to all those who need it, in the United States and around the world," she said. "The track record thus far, has, unfortunately, not been a good one."

With a month's course of lenacapavir as HIV treatment costing nearly $3,500, it's unclear how pricey the preventive form of the drug might be. A Gilead spokesman told NBC News that lenacapavir's price as twice-yearly PrEP may not end up reflecting its current price as treatment.

Insurance coverage could be another hurdle to accessing twice-yearly lenacapavir.

Truvada went off patent in 2020 and is now widely available to prevent HIV for as little as $20 a month. Insurers might balk at allowing coverage for an injection that could cost exponentially more.

HIV/AIDS remains a major threat to people living in the developing world, especially sub-Saharan Africa. Since the release of the trial involving African women, HIV activists have put pressure on Gilead to make lenacapavir PrEP affordable to people in low-income nations.

In its news release, Gilead said that it "is committed to making lenacapavir available in the countries where the need is greatest, including expediting voluntary licensing partners to supply high-quality, low-cost versions of lenacapavir. Gilead is actively working to finalize these contracts."

More information

There's more on PrEP at the U.S. Centers for Disease Control and Prevention.

SOURCES: Gilead Sciences, news release, Sept. 12, 2024; NBC News