Scientists Frustrated in Search for Genital Herpes Vaccine

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.

Stanberry said final results from the trial should be available by 2009, and -- if the vaccine proves effective -- a shot might be approved by 2010.

However, like most modern vaccine trials, the Herpevac trial relies on a piece or "subunit" of HSV to prime the human immune system against incoming virus.

Another researcher is advocating the use of the live -- but greatly weakened -- form of the virus, instead.

The problem with the subunit approach is that its effects don't last, said William Halford, a virologist at Montana State University, in Bozeman. "Once you deliver it into someone's body, it's there, but, in a few weeks, it is gone," he said.

Live virus vaccines have a long and effective history. In fact, one of the few effective vaccines against any herpes strain -- the chickenpox/shingles (herpes zoster) shot -- was developed from live virus back in the 1960s.

Since that time, doctors have gotten more skittish about injecting people with a live form of the virus, however, so the subunit approach took precedence.

But Halford believes it is time to revisit the idea of a live virus herpes vaccine.

"All we really have to do is to figure out a way to take away some of the genes or proteins that the virus needs to cause actual disease," he said. In other words, people would be infected with a very weak form of HSV, one that is sufficient to trigger a sustained immune response but too frail to trigger disease outbreaks.