- Herpes simplex virus type 2 (HSV-2) is a major cause of genital herpes. It can also cause serious infection in newborns and in people with weakened immune systems. It increases the risk of getting an HIV infection and of spreading HIV to someone else. Therefore, a vaccine that could prevent genital herpes could improve the general health of the world s population. Researchers want to study whether a new vaccine, HSV529, which may be used in the future to prevent herpes infections, is safe.