At age 20 months hearing and child development are assessed in the follow-up. Hearing will be assessed with Brainstem Evoked Response Audiometry with the Vivosonic Integrity. Child development will be assessed with the Bayley Scales of Infant Development III (official Dutch translation) and parents will fill in the Dutch Child Development Inventory (NCDI) which will give more detailed information on communicative development of their child. The hearing assessment and developmental examination will be fulfilled during a home visit. Viral loads in blood and urine will be monitored during antiviral treatment as well as twice in the control group.