Against Chikungunya Virus and Neonatal Infection

The goal of this clinical trial is to learn if administration of plasma, from a whole blood donation from an individual who has declared a Chikungunya infection for less than 6 months , to a newborn, whose mother has a peripartum chikungunya infection, will have an impact on the proportion of newborns surviving without encephalitis/encephalopathy (EE) within the first 5 days of life. Researchers will compare results to an observational study of 30 newborns who couldn't have been proposed to participate at the clinical trial, because of delay of diagnosis or delay of transfer to hospital which doesn't allow transfusion or parents not accepting plasma transfusion to the newborn. Participants of the clinical trial will: * receive a transfusion, * visit the clinic and undergo biological tests every day until day 7 and once between 1 and 3 months. Participant of observational study as part of their regular medical care, and biological data will be reused for the research from the mother's diagnosis until the newborn reaches 3 months of age