IFNAR−/−/IFNGR−/− (AG129) mice do not survive infection, yet STAT1−/−/IFNGR−/− mice remain healthy, demonstrating that STAT2 alone provides sufficient signaling via the type I IFN pathway for a functional antiviral response, despite the absence of both STAT1 and type II IFN signaling. Here, STAT1 is linked to infection.