Type I IFNs play a key role in the earliest responses to viral infections and it is well known that several Flaviviruses interfere with IFN production or activity [47,48], however other factors such as age, neuronal and astrocyte maturation are likely important factors for the establishment of productive infections as observed with other neurotropic RNA viruses including Sindbis, Chikungunya and Tacaribe virus, where neonate but not adult mice develop productive infections [25,26,49]. This evidence concerns the gene IFNA1 and viral infectious disease.