Sept. 17, 2000 (Toronto) -- A new vaccine against genital herpes protects some women, but not all, from developing symptoms of the disease. The vaccine failed to work in men, and it worked only in women who have never been infected with a related herpes virus that causes cold sores, according to results of two studies presented here at a meeting of infectious disease specialists.
"We've got a grip on herpes virus for the first time," says Spotswood Spruance, MD, of University of Utah School of Medicine in Salt Lake City, who was lead researcher for one of the two trials.
If approved by regulators, the vaccine could one day be given to uninfected teen-age girls to protect them from future exposure to the herpes virus, says Lawrence Stanberry, MD, PhD, who directed the other trial. Stanberry is director of the Center for Vaccine Development at the University of Texas Medical Branch at Galveston.
The virus that causes genital herpes infections, herpes simplex virus type 2 (HSV-2), is closely related to the virus that causes cold sores, herpes simplex virus type 1 (HSV-1). The vaccine, which was injected in the arm three times over a six-month period, protected only women who had never been infected with HSV-1, from developing symptoms of the infection.
In the first of the two studies presented at the meeting, Stanberry and his colleagues compared the effects of the vaccine on a broad cross-section of men and women who had never been infected with genital herpes, but who were in committed relationships with a partner who did suffer from the infection.
When the researchers examined the entire group, they found that the vaccine did not significantly reduce the odds of getting the illness. But when they looked specifically at women who had never been infected with HSV-1, that changed. They found that vaccinated women were 73% less likely to develop symptoms of genital herpes than women who received mock vaccinations, whereas the vaccine has no effect in men.
Knowing these results, Spruance's group designed another trial to look only at women who had never been infected with HSV-1. The vaccine protected these women from developing symptoms about as well as it had in the first trial.
"This was the first demonstration of a gender-specific effect of a vaccine on a disease," Stanberry said. It's not clear why the vaccine works only in women, but the researchers speculate that the difference occurs because of differences in anatomy and route of infection. The vaccine generates a response from the body's immune system in both sexes, but in women, they have a chance to fight the virus in the vagina's fluid before infection occurs. Men are infected through breaks in the skin, so they can't fight infection that way, Spruance speculates.
"It looks like it has a significant effect," says William Craig, MD, professor of medicine at the University of Wisconsin in Madison. But he cautions that the vaccine could have limited effects because it will only work on the 20% or so of adult women who have never been infected with HSV-1.