Importantly, unlike the results in WT MEF, ROCV/WNV-prME chimeric virus reached similar to the parental ROCV titres at 48 h and 72 h after infection in IFNAR−/− MEF (Fig. 2d) indicating that chimerization did not avertedly affect replication of this chimeric virus in the absence of functional IFN-α/β response. This evidence concerns the gene IFNAR1 and infection.