Scientists Frustrated in Search for Genital Herpes Vaccine

Although the two strains are similar and can infect either mouth or genitalia, HSV-1 is the prime cause of oral herpes (cold sores and fever blisters), while HSV-2 is the usual source of genital infections.

Another tactic keeps herpes well-shielded from immune attack. Unlike pathogens that spread in readily accessed blood, HSV hides out in nerve cells called dorsal ganglia, located in the back. Specific triggers, such as sun exposure or stress, can send the virus traveling through nerve pathways to mucosal sites of activity in the genitalia, mouth and even eyes.

These nerve cells are "a protected site, immunologically," explained Dr. Lawrence Stanberry, director of the Sealy Center for Vaccine Development at the University of Texas Medical Branch in Galveston. "Needless to say, we don't like to have our immune system attacking our nerves," he said, so vaccines with that kind of reach are hard to develop.

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And yet, progress is being made. The Herpevac trial, funded by the U.S. National Institutes of Health and drug maker GlaxoSmithKline, is focused on a preventive vaccine aimed solely at uninfected women. Preliminary, phase III studies completed last year found the vaccine to be 73 percent effective in shielding young women from infection after exposure to HSV-2.

A 73 percent effectiveness rate may not sound all that impressive, but Stanberry -- also an investigator on the Herpevac trial -- said no one is expecting 100 percent immunization.

"What one hopes for with a vaccine is that you get very high rates of effectiveness and then very broad uptake of the vaccine [in the population]," he explained. "So then, if almost everyone gets immunized, then the disease simply doesn't circulate in the population to the same extent."

Reducing the "pool" of available virus will be vital to lowering the infection rate, researchers say, because the Herpevac shot does not protect uninfected men and cannot eliminate HSV from people who are already infected.

The Herpevac trial is currently wrapping up recruitment of 7,000 healthy, HSV-negative U.S. women between the ages of 18 and 30. Participants will receive either the vaccine or a placebo and then be followed for 18 months to see if they become infected.