There’s herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2). “HSV-1 and HSV-2 are different but closely related viruses,” says Dr. Christine Johnston, MPH, who is the Associate Medical Director of the Virology Research Clinic at the University of Washington. Johnston explains that both are transmitted through close mucosal or skin contact with infected secretions. HSV-1 primarily causes oral outbreaks, also known as cold sores, and HSV-2 usually causes genital outbreaks. But HSV-1 can also cause genital outbreaks through oral-to-genital contact, according to the CDC. According to Johnston, genital HSV-1 is less likely to recur than HSV-2, and there’s less asymptomatic shedding (transmitting the virus without realizing it) with HSV-1 than with HSV-2.
As of 2017, there is not currently a herpes vaccine available to prevent HSV-1 or HSV-2. (There is a vaccine available for another virus, herpes zoster; however, despite the similar name, it actually refers to the shingles virus. And, in fact, shingles occurs due to the reactivation of yet another virus, varicella zoster, which causes chicken pox.)
A 2004 study in the New England Journal of Medicine found that suppressive therapy decreases the risk of HSV-2 transmission from symptomatic, infected partners to uninfected partners by 48%. So “the risk of transmission is significantly reduced, but cannot be eliminated even with suppressive therapy,” Johnston explains, and she stresses that the virus can be passed along even without signs or symptoms.