This annual shot might protect against HIV infections

You never hear “100%” in medicine. The trial was the most successful we’ve ever seen for HIV prevention. The drug was safe, too (it’s already approved to treat HIV infections). And it only needed to be injected twice a year to offer full protection.

This week, the results of a small phase I trial for once-yearly lenacapavir injections were announced at a conference in San Francisco. These early “first in human” trials are designed to test the safety of a drug in healthy volunteers. Still, the results are incredibly promising: All the volunteers still had the drug in their blood plasma a year after their injections, and at levels that earlier studies suggest will protect them from HIV infections.

I don’t normally get too excited about phase I trials, which usually involve just a handful of volunteers and typically don’t tell us much about whether a drug is likely to work. But this trial seems to be different. Together, the lenacapavir trials could bring us a significant step closer to ending the HIV epidemic.

First, a quick recap. We’ve had effective pre-exposure prophylactic (PrEP) drugs for HIV since 2012, but these must be taken either daily or just before a person is exposed to the virus. In 2021, the US Food and Drug Administration approved the first long-acting injectable drug for HIV prevention. That drug, cabotegravir, needs to be injected every two months.

But researchers have been working on drugs that offer even longer-lasting protection. It can be difficult for people to remember to take daily pills when they’re sick, let alone when they’re healthy. And these medicines have a stigma attached to them. “People are concerned about people hearing the pills shake in their purse on the bus … or seeing them on a medicine cabinet or bedside table,” says Moupali Das, vice president of HIV prevention and virology, pediatrics, and HIV clinical development at Gilead Sciences.