IFNL1 and infection: Although individual therapeutic treatment regimens with either IFN-λ or IFN-γ in aged Ifnar1−/− both conferred only limited protection against SARS-CoV-2 induced disease and lethality (Fig. 7 B and Fig. S4 D), the combinatorial therapeutic treatment with IFN-λ1/3 and IFN-γ prevented morbidity exceeding 10% of body weight loss in an otherwise lethal infection (Fig. 7 E) and significantly reduced viral replication in upper airways and lungs (Fig. 7 F).