US researchers have launched an early-stage clinical trial of an investigational vaccine designed to prevent genital herpes disease, the National Institute of Allergy and Infectious Diseases (NIAID) said Friday. Genital herpes, one of the most common sexually transmitted infections in the United States, is mostly caused by infection with herpes simplex virus type 2 (HSV-2). There is no vaccine to prevent genital herpes. "Although genital herpes is treatable, it is a lifelong infection that can exact a substantial psychological and physical toll on infected individuals and places them at higher risk of acquiring HIV," NIAID Director Anthony Fauci said in a statement. "A protective vaccine would help to reduce significantly the spread of this all-too-common sexually transmitted infection," Fauci added. The Phase I trial, led by researchers at NIAID's Laboratory of Infectious Diseases, will test an investigational HSV-2 vaccine candidate, called HSV529, for safety and the ability to generate an immune system response. The experimental product is a replication-defective vaccine, meaning that scientists have removed two key proteins from the vaccine virus so that it cannot multiply to cause genital herpes, the NIAID said. The clinical trial will enroll 60 adults aged 18 to 40 and is expected to be completed by October 2016, it added.