Herpes viruses can cause painful itching and sores, but most people who are infected show no symptoms, which is why it is spread so easily. Recent evidence suggests that a co-infection of HPV and HSV-2 doubles the risk of cervical cancer. Herpes infections are also thought to accelerate the spread of the human immunodeficiency virus. And babies who contract the herpes virus from their mothers are at a high risk of death. From 2,500 to 3,000 such cases occur in the United States each year.
A team led by Dr. Lawrence Stanberry of the University of Texas Medical Branch in Galveston enrolled 978 women and 1,736 men whose partners had genital herpes. Half received the vaccine in three injections and half a placebo.
The team reported in the New England Journal of Medicine that the vaccine protected 74% of women who had never been exposed to either HSV-2 or HSV-1. It was much less effective in women who had been exposed to HSV-1, and for reasons that mystify the researchers, was not effective at all in men.
Researchers expect to make improvements in the efficacy of the vaccine. But even if they do not, Ebel said, mathematical modeling suggests that widespread use of a vaccine that is 74% effective only in women could still produce a significant reduction of cases in both men and women.
The National Institute of Allergy and Infectious Diseases said Wednesday that it will begin enrolling 7,550 women this week in a much larger trial. Enrollment will be restricted to women who have not been exposed to either form of the virus.
Because neither vaccine is effective on a person who has been exposed to the virus, researchers say it may necessary to vaccinate girls before they have any sexual experiences, probably around age 12 or 13. "It would eventually become part of our vaccine protocol," Carlin said.