It's crucial to have the medicine handy and take it right away for the best chance of stopping an outbreak, says Spruance, the lead investigator of the cold sore study. The tingling, itching or burning sensation is a sign that the virus has become active and is replicating. Most herpes sufferers can identify those symptoms easily, he says. "They know when they're getting one."
Caprio, now 30, says she has abandoned daily preventive medication and will now carry the single-day dose with her to prevent outbreaks.
"I think it's awesome," the New Jersey woman says. "The problem with herpes is that when you have breakouts, they last a week -- a week of pain and symptoms. If you can identify the symptoms and have the medication on hand and wipe it out, that really helps you emotionally."
Most doctors believe that not enough people obtain treatment for herpes. Even those with infrequent outbreaks should inquire about medication, experts say. Herpes can be transmitted during outbreaks and even when someone is asymptomatic. Moreover, a pregnant woman with an active infection -- whether symptoms are apparent or not -- can transmit the virus to her baby at birth, causing serious problems such as seizures, blindness, spasticity or death.
"People with mild or infrequent outbreaks are unlikely to seek medical attention," Tyring says. "But they could still spread it to someone else, or a baby could be born to a mother who has it. That is the worst-case scenario."
Now, focus is on vaccine
The recent approval of one-day dosing of Famvir suggests that researchers have gotten the most they can out of the nucleosides, Spruance says. "These latest trials represent the last point on the learning curve with these drugs. We've really reached the end of this paradigm."
But a new research focus is emerging -- one that aims to prevent herpes infections. A government-funded study testing a herpes vaccine is underway at more than 20 sites across the country. The study of 7,500 women will examine whether the vaccine, given in three doses within six months, can prevent infections in women ages 17 to 35 who have not been exposed to either HSV-1 or HSV-2.
Earlier studies of the vaccine showed it wasn't effective in women who were already exposed to either or both of the viruses. It also didn't work in men. But it was found to protect against infection in more than 70% of women who weren't previously exposed to HSV-1 or HSV-2.
Experts aren't sure why the vaccine doesn't work in men. However, if the vaccine is eventually approved in women, widespread immunization could help protect men too, says Dr. Joel Ward, director of the Center for Vaccine Research at UCLA and the lead investigator for the local arm of the vaccine trial.
"If it's not circulating in the population, then men won't get herpes," Ward says.
The study is scheduled to conclude next year and, if successful, would be the second vaccine against a sexually transmitted disease. A vaccine against human papilloma virus, which can cause cervical cancer, was approved this year for use in girls and women ages 9 to 26.
How well that vaccine, called Gardasil, is accepted by the public may point to the success of a future herpes vaccine, experts say. Vaccines for STDs need to be administered in childhood, well before the initiation of sexual activity. But parents may prove reluctant to consider their child's risk for infection later in life.
"Everybody is interested in what the public response will be to Gardasil," says Dr. Judy Falloon, the chief medical officer for the herpes vaccine trial at the National Institutes of Health. It may be harder to convince parents of the importance of a herpes vaccine, she says. "HPV can be thought of as a cancer vaccine. It doesn't have the stigma of an STD. Herpes is very stigmatized."
Ward believes that once parents understand the benefits, they won't hesitate to protect kids from any potential threat.
"Over the next few years, young teens, ages 10 to 12, will be offered a number of vaccines that can make their adult years safer than our adult years," he says. "If I can prevent anything, why not do it?"