This is a study to find out the right dose of a medicine called valacyclovir for newborns who might get a virus called neonatal herpes simplex virus (HSV). Valacyclovir is a medicine that turns into acyclovir in the body, which can fight the virus. The study will have two groups of babies. In the first group, eight babies will take the medicine. Doctors will check if the medicine is safe and how much of it reaches the baby's body. If all goes well, a second group of eight babies will join, and they might get a different dose based on what was learned from the first group. Babies can join if their moms had a history of HSV and took valacyclovir before birth. This study helps find a safe and effective dose for babies.

• The study involves two groups of eight newborns each.
• Participation involves taking valacyclovir and monitoring at home.
• Babies must meet specific health criteria to join the study.