Plays a major role in antagonizing the type I IFN-mediated antiviral response. Acts cooperatively with NS1 to repress activation and nuclear translocation of host IFN-regulatory factor IRF3. Interacts with the host cytoplasmic sensor of viral nucleic acids RIGI and prevents the interaction with its downstream partner MAVS. Together with NS2, participates in the proteasomal degradation of host STAT2, IRF3, IRF7, TBK1 and RIGI through a NS-degradasome involving CUL2 and Elongin-C. The degradasome requires an intact mitochondrial MAVS. Induces host SOCS1 expression. Induces activation of NF-kappa-B. Suppresses premature apoptosis by an NF-kappa-B-dependent, interferon-independent mechanism promoting continued viral replication