An international team of researchers found that taking a single daily dose of an approved antiviral drug known as valacyclovir can reduce the transmission of genital herpes to uninfected partners by 50 percent.

The team of researchers was led by Larry Corey, head of the Fred Hutchinson Cancer Research Center’s infectious disease program and UW professor of laboratory medicine, medicine and microbiology. They studied nearly 1,500 heterosexual monogamous couples in which one partner had genital herpes and the other did not. Infected partners who received a standard oral dose each day of valacyclovir were half as likely to transmit herpes simplex type 2 (HSV-2) than infected partners given a placebo.

The strategy potentially could be applied to combat the spread of other sexually transmitted diseases that are caused by viruses. Genital herpes is caused by HSV-2 and infects about 50 million Americans over age 20.

The study was conducted at 96 centers in the United States, Canada, Europe, South America, and Australia. Collaborators at the UW included Anna Wald, associate professor of medicine, laboratory medicine and epidemiology, and R. Ashley Morrow, professor of laboratory medicine and virology and director of the Viral Diagnostic Laboratory at Children's Hospital and Regional Medical Center.