Promising preclinical experiments show that, under specific and monitored conditions, ultraviolet-A (UVA) exposure reduces certain bacteria, fungi, and viruses including coronavirus-229E without harming mammalian columnar epithelial cells. We aimed to evaluate the safety and effects of UVA therapy administered by a novel device via endotracheal tube in critically ill subjects with SARS-CoV-2 infection. Methods: Five newly intubated mechanically ventilated adults with SARS-CoV-2 infection, with

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... n endotracheal tube size 7.5mm or greater, were treated with UVA for 20 minutes daily for 5 days, and followed for 30 days. Results: Five subjects were enrolled (mean age 56.6yrs, 3 male). At baseline, all subjects scored 9/10 on the WHO clinical severity scale (10=death) with predicted mortality ranging from 21 to 95%. Average log changes in endotracheal viral load from baseline to day 5 and day 6 were -2.41 (range -1.16 to -4.54; Friedman P=0.002) and -3.20 (range -1.20 to -6.77; Friedman P<0.001), respectively. There were no treatment-emergent adverse events. One subject died 17 days after enrollment due to intracranial hemorrhagic complications of anticoagulation while receiving extracorporeal membrane oxygenation. The remaining subjects clinically improved and scored 2, 4, 5, and 7 on the WHO scale at day 30. In these subjects, the slope of viral load reduction during UVA treatment correlated with the slope of improvement in clinical WHO severity score over time (Spearman rho=1, P<0.001). Conclusion: In this first-in-human study, endotracheal UVA therapy under specific and monitored settings, was safe with a significant reduction in respiratory SARS-CoV-2 viral burden over the treatment period.