Although the primary objective of the trial is to assess the safety of hyperimmune human intravenous immunoglobulins in neonates, a clear potential individual benefit is expected for participating neonates, namely a decreased risk of development of a severe form of Chikungunya, especially in terms of high-burden central nervous system complications (seizures, cerebral palsy). This is a major issue since the first case of complicated neonatal Chikungunya has already occurred in Martinique in January 2014 (clinical manifestations included fever, pain, skin rash, and encephalopathy in a four-day-old neonate).