Most people have heard of a cold sore flaring up at the worst moment, or felt the dread of one coming on. For most of us, the familiar pills clear it in a few days. For some, those pills stop working at all.
The US Food and Drug Administration approved a new herpes drug called Hovilpri on October 9, 2026, according to Contagion Live. The active ingredient is pritelivir.
The drug is cleared for adults with weakened immune systems whose herpes lesions no longer respond to the standard antivirals acyclovir, valacyclovir and famciclovir.
Herpes simplex is one of the most common viral infections in the world. According to the World Health Organization, about 3.8 billion people under 50, roughly 64 percent of that group, carry the oral form (HSV-1).
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Another 520 million people aged 15 to 49 carry the genital form (HSV-2).
Why standard pills sometimes fail
The pills most doctors reach for, acyclovir and its cousins, have been around for decades. They slip in and act like a building block the virus needs to copy its DNA, which jams the copying process.
That trick depends on an enzyme inside the herpes virus called thymidine kinase. If the virus mutates and loses that enzyme, the pills no longer activate, and the lesions keep spreading.
This is a real problem in people whose immune systems cannot keep the virus in check on their own.
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A new target the virus cannot work around
Pritelivir takes a completely different approach. It is the first drug in a class called helicase-primase inhibitors, which block a separate pair of enzymes the virus needs to unwind and copy its DNA.
Because the drug does not need the thymidine kinase enzyme to work, it stays active against the strains that have become resistant to acyclovir. This mechanism had not been used in an approved herpes treatment before.
In the trial that led to the approval, called PRIOH-1, researchers randomly assigned 101 immunocompromised adults with stubborn HSV lesions to either pritelivir or the current fallback treatments. Most of those fallbacks are intravenous drugs with harsh side effects.
By day 28, lesions had healed completely in about 63 percent of the pritelivir group, compared with 34 percent on the older treatments, according to Dermatology Times. By day 42, the gap had widened to about 82 percent against 42 percent.
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Side effects were also less common. About one in five patients on pritelivir had an adverse reaction, versus more than half on the older drugs.
Only 2 percent of pritelivir patients stopped treatment because of side effects, compared with 20 percent in the other group. The most common complaint was a headache.
Dr. Genovefa Papanicolaou of Memorial Sloan Kettering Cancer Center, one of the trial investigators, said these patients face especially tough forms of the infection.
"In patients with blood cancers or those who have undergone stem cell transplantation, refractory HSV infections can be prolonged, painful, and difficult to treat," she said.
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Who can get it, and who cannot
Hovilpri is not approved for ordinary cold sores or genital outbreaks in otherwise healthy people. The green light applies to immunocompromised adults.
That includes transplant recipients, people living with HIV, and those being treated for cancer or autoimmune disease. Anyone with worsening herpes lesions while on immune-suppressing treatment should talk to their doctor about whether the new drug fits their situation.
Asahi Kasei Therapeutics, which makes the drug, says tablets are expected to reach US pharmacies before the end of 2026.
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This article is made and published by Aksel Kryhlmand, who may have used AI in the preparation.