Why Don't We Have a Herpes Vaccine?

More than half the world could use it.

Mar 3 2017, 1:00pm

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Let's start with the stats, because they're jaw-dropping.

Roughly one in six Americans is infected with genital herpes, according to the CDC. More than half of all Americans—and two-thirds of the world's population—are infected with oral herpes. That makes the herpes simplex virus (HSV) one of the most common viral infections on the planet, and any company that develops a working vaccine could make billions.

So what's the holdup? Experts say past failures and the virus's cagey nature have combined to confound both researchers and the drug companies who fund them.

As you probably know, herpes is transmitted via skin-to-skin contact. When a herpes carrier is experiencing a "flare-up"—that is, an outbreak of the mouth or genital sores that are the infection's hallmark—he or she can pass that form of the virus on to a partner via smooching or sex. (In some cases, a carrier is contagious even when not experiencing skin symptoms.)

Once you're infected, your symptoms can vary dramatically. While roughly 30 percent of sufferers have frequent blister outbreaks that "make them miserable," the other 70 percent hardly notice the infection, says Harvey Friedman, a professor of medicine at the University of Pennsylvania. And because symptoms can be mild, a lot of people have no idea they're infected, he adds.

Unpleasant symptoms aside, there are more serious reasons to fear herpes. "People who have genital herpes have a four-fold risk of acquiring HIV, if exposed, compared to those who don't have [herpes]," Friedman says. And those infected with oral herpes are at an increased risk for encephalitis (brain inflammation) and eye disease. Also, infants born to women suffering from a genital herpes flare-up can suffer deadly complications. "There's not urgency about a herpes vaccine like there is with Ebola or Zika, but there has been a chronic need for many years," he says.

Friedman would know, because he's arguably in the best position to satisfy that need; he's leading research into one of the most promising herpes vaccines ever developed.

"Previous vaccines have aimed to block the virus's entry into cells," he says. To accomplish that, most vaccines encourage your immune system to develop specific infection-blocking antibodies. But herpes is a crafty adversary. "The virus contains evasion molecules that allow it to escape your immune system's antibodies," Friedman explains. "That's why we've developed a two-pronged strategy." Along with encouraging your immune system to create those cell entry-blocking antibodies, Friedman's vaccine also prevents the herpes virus from putting on a disguise that hides it from your immune system.

The early returns are encouraging. In recent lab experiments, Friedman and his colleagues found their vaccine was 98 percent effective at blocking genital herpes infections among guinea pigs. Their vaccine also seemed to protect macaque monkeys from the virus.

But while positive results in rodents and non-human primates are good first steps, other vaccines have hurdled that bar only to fall far short when it came time for broader human trials. Notably, a vaccine GlaxoSmithKline put its chips on a few years ago looked good in some small human trials, but bit the dust when those trials were expanded.

"We can be misled by animal models," Friedman acknowledges. He says herpes is "made to infect humans," and that past failures of even very promising drugs have made major pharmaceutical companies and investors leery.

As of today, Friedman and his team are in negotiations with various drug company backers. Once they've found a partner, Friedman says he and his colleagues will conduct some follow-up experiments to substantiate the vaccine's efficacy before moving on to human testing. "We're probably still two years away from human trials," he says.

Of course, there are other researchers working on herpes vaccines—as well as treatments. But none are farther along the road to approval and adoption than Friedman's. So while there's hope, the hopeful will have to sit tight a while longer.