The recently emerged severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is the causative agent of the devastating
COVID-19 lung disease pandemic. Here, we tested the inhibitory activities of the antiviral interferons of type I (IFN-alpha)
and type III (IFN-lambda) against SARS-CoV-2 and compared them with those against SARS-CoV-1, which emerged in 2003. Using
two mammalian epithelial cell lines (human Calu-3 and simian Vero E6), we found that both IFNs dose-dependently inhibit SARS-CoV-2.
In contrast, SARS-CoV-1 was restricted only by IFN-alpha in these cell lines. SARS-CoV-2 generally exhibited a broader IFN
sensitivity than SARS-CoV-1. Moreover, ruxolitinib, an inhibitor of IFN-triggered Janus kinase (JAK)/signal transducer and
activator of transcription (STAT) signaling, boosted SARS-CoV-2 replication in the IFN-competent Calu-3 cells. We conclude
that SARS-CoV-2 is sensitive to exogenously added IFNs. This finding suggests that type I and especially the less adverse
effect–prone type III IFN are good candidates for the management of COVID-19.