TORONTO â€“ For the first time, a vaccine appears to protect against infection with the herpes virus, but it works only in women, medical researchers here said Sunday.
Although previous attempts to develop a herpes vaccine have been disappointing, the new vaccine proved 73 percent to 74 percent effective in preventing genital herpes among women. The women in the study were considered at high risk for herpes because their sexual partners were infected with the virus.
"We've got a grip on the herpes virus for the first time," said Dr. Spotswood Spruance of the University of Utah, who presented his research in Toronto during the annual meeting of the Interscience Conference on Antimicrobial Agents and Chemotherapy.
The results mean that about 70 percent of women who would have probably become infected did not. For example, about 10 percent of women in one study who were not vaccinated developed herpes, while the rate among vaccinated women was about 3 percent.
The news wasn't so good for men. For reasons the scientists can only speculate about, infection rates among vaccinated and unvaccinated men in the study weren't significantly different.
The vaccine also didn't make much of a difference when women had already been exposed to one type of herpes virus. Two kinds of herpes virus are common in the United States. The first, abbreviated HSV-1, is famous for causing cold sores. The second, abbreviated HSV-2, causes genital herpes. While the viruses are close cousins, they cause very different diseases.
But they are so closely related that, in the two studies presented Sunday, women who had been infected with HSV-1 already had some immune protection from HSV-2. The vaccine is designed to prevent HSV-2, which affects an estimated one in five U.S. adults and one in four women. In the new research, a childhood cold sore offered about as much protection as the vaccine.
For this reason, a herpes vaccine such as the one discussed Sunday would be best targeted to adolescent girls, Dr. Spruance said, when infection rates for HSV-1 are still low. By age 35, about 65 to 70 percent of the population tests positive for HSV-1 infection, he said. Doctors would not want to rely on cold sores to protect against genital herpes infections, he said, because many people become infected at an early age. Furthermore, studies on the protection cold sores offer haven't been consistent.
"You're going to have to target the youngest population you can," said Dr. Lawrence Stanberry, director of the Center for Vaccine Development at the University of Texas Medical Branch at Galveston. Dr. Stanberry was also involved in the research.
The two studies combined involved almost 3,000 volunteers in North America, Europe and Australia who were not infected with genital herpes but had a regular sexual partner who was. Each received either three doses of the vaccine, or three doses of a shot that only looked like the vaccine.
The vaccine contained a piece of the herpes virus's outer shell, designed to fool the body into thinking a person had been infected, and provoke a full-fledged immune response. It also contained a substance to gear up the immune system. Dr. Spruance theorized that previous herpes vaccines failed to work because they were not potent enough.
While he'd like good results for both genders, Dr. Spruance said, "For women, there was a fairly striking effect."