BackgroundBaricitinib, an oral selective Janus kinase 1 and 2 inhibitor, improved outcomes in a previous randomized controlled trial of hospitalized adults with COVID-19, in combination with remdesivir. MethodsIn this phase 3, global, double-blind, randomized, placebo-controlled trial, 1525 hospitalized adults with COVID-19 receiving standard of care (SOC) were randomly assigned (11) to once-daily baricitinib 4-mg (N=764) or placebo (N=761) for up to 14 days. SOC included systemic corticosteroids in [~]79% of participants (dexamethasone [~]90%). The primary endpoint was the proportion who progressed to high-flow oxygen, non-invasive ventilation, invasive mechanical ventilation, or death by day 28. A key secondary endpoint was all-cause mortality by day 28. ResultsOverall, 27.8% of participants receiving baricitinib vs 30.5% receiving placebo progressed (primary endpoint, odds ratio 0.85, 95% CI 0.67-1.08; p=0.18). The 28-day all-cause mortality was 8.1% for baricitinib and 13.1% for placebo, corresponding to a 38.2% reduction in mortality (hazard ratio [HR] 0.57, 95% CI 0.41-0.78; nominal p=0.002); 1 additional death was prevented per 20 baricitinib-treated participants. Reduction in mortality was seen for all pre-specified subgroups of baseline severity (most pronounced for participants on high-flow oxygen/non-invasive ventilation at baseline [17.5%, baricitinib vs 29.4%, placebo; HR 0.52, 95% CI 0.33-0.80; nominal p=0.007]). The frequency of adverse events, serious adverse events, serious infections, and venous thromboembolic events was similar between groups. ConclusionsWhile reduction of disease progression did not achieve statistical significance, treatment with baricitinib in addition to SOC (predominantly dexamethasone) significantly reduced mortality with a similar safety profile between groups of hospitalized COVID-19 participants.