Medical researchers may be finally closing in on an effective vaccine for the genital sores caused by the herpes simplex virus, following exciting results from recent studies in guinea pigs and monkeys.

Human safety trials of one vaccine candidate, composed of three key viral proteins, could begin in less than 18 months.

One of the most common sexually transmitted diseases, genital herpes is characterized by tingly, itchy, inflamed, and painful lesions on the skin on and around the genitals and within the vagina, urethra, and anus that resolve and recur intermittently. The infection, caused predominantly by the HSV-2 herpes simplex strain and somewhat less frequently by HSV-1, is incurable, and past attempts to develop both treatments and vaccines have failed.

Herpes simplex’s trickiness stems from its ability to evade the body’s immune system – and circulating anti-viral drug agents – by lurking in neurons of the peripheral nervous system whose endings, or axons, are in the genital skin. As many as two out of three people permanently harbor HSV-1, and one in five have HSV-2; and though only a fraction of individuals experiences observable symptoms, even those without active lesions can pass it on to others. All HSV infections are known to put people at higher risk of contracting HIV if exposed to that virus.

The most recent candidate, created by a team at Louisiana State University, uses a strain of live-attenuated virus that was engineered with disabling mutations in the protein that allows the virus to enter axons. Their assessment in guinea pigs, published this week in the journal Vaccine, showed that none of the nine guinea pigs who received injections (plus two boosters) of the engineered strain became infected after exposure to a highly virulent HSV-2 strain, whereas all nine of the unvaccinated animals did.

According to New Scientist, lead author Konstantin Kousoulas reports that further, as-of-yet unpublished experiments suggest that the vaccine can also mobilize the immune system in guinea pigs already infected with a pathogenic herpes strain and that the vaccine is safe in non-human primates.

“We think it has tremendous potential as both a preventative and therapeutic vaccine,” Kousoulas told the magazine.

Examples of herpes simplex 2 infections and a visualization of the virus itself. Fitzpatrick's Color Atlas and Synopsis of Clinical Dermatology, Eighth Edition, 2017

In January 2017, the University of Pennsylvania group behind the protein fragment vaccine candidate published breakthrough findings from a series of evaluations in animals.

Their study demonstrated that introducing the immune system to three viral surface glycoproteins – two involved in immune evasion and one that aids in entering neurons – could curb the development of genital lesions and prevent the virus from successfully replicating in the vaginal tissue of guinea pigs, a sign that wouldn’t be transmissible to other individuals.

After exposure to an infamously pathogenic HSV-2 strain from sub-Saharan Africa, 97 percent of guinea pigs that received one injection and 99 percent of those that also got a booster were symptom-free. The group's tests in macaques hinted that a regimen of three vaccine injections could be ideal for inducing a strong immune response against potent viral particles in primates such as ourselves.

In October 2017, lead researcher Dr Harvey Friedman stated that his team are working with drug companies to initiate human testing. He conceded that although animal models have a spotty track record in terms of predicting vaccine success in people, he has a positive outlook on the potential of his candidate.

[H/T: New Scientist]