- Infants known to be born to women who are human immunodeficiency virus (HIV) positive (but HIV testing is not required for study entry). These infants are at known risk of acquiring HIV, which would alter their immune response to other infections, including herpes simplex virus (HSV) infection. Additionally, they may be receiving antiretroviral and/or antiviral drugs during the time in which the study of suppressive oral acyclovir is being conducted. As such, they will be excluded if the mother's positive HIV status is known at the time of evaluation for study inclusion. If at any point following enrollment it is learned that an infant is HIV positive, however, he/she will be continued on the study protocol.