Notes: EIDD-2749 is an antiviral ribonucleoside analog.{64932} Incorporation of EIDD-2749 into RSV or severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA inhibits viral RNA-dependent RNA polymerase (RdRp) and induces transcriptional stalling in cell-free assays. It reduces viral yield in HEp-2 cells infected with clinical isolates of respiratory syncytial virus (RSV; EC50s = 0.61-1.2 µM). EIDD-2749 reduces apical virus shedding in RSV-infected isolated human airway epithelial (HAE) cells (EC50 = 55 nM). In vivo, EIDD-2749 (5 mg/kg) reduces lung virus load in a mouse model of RSV infection. It also reduces nasal viral titers in a ferret model of SARS-CoV-2 infection when administered at doses of 15 and 50 mg/kg.