1339. Effects of Tixagevimab-Cilgavimab in Clinical Practice is Consistent with Preliminary Neutralization Studies

BACKGROUND: Emergency use of tixagevimab-cilgavimab was based on data collected prior to the emergence of SARS-CoV-2 omicron variant and subvariants. Dosing recommendations changed twice based on neutralization data alone, leading to patients receiving different doses at varying intervals. We provide real-world data on efficacy of tixagevimab-cilgavimab in immunocompromised patients throughout 2022, including the incidence and timing of infection based on dosing scheme. METHODS: Charts of 471 patients who received and 126 patients who declined administration of tixagevimab-cilgavimab were analyzed through December 14(th), 2022. We evaluated incidence of SARS-CoV2, severity, risk factors and vaccination status. For analysis, we grouped patients with similar dosing: Group A received one initial dose of 150mg/150mg of tixagevimab-cilgavimab, Group B received at least 300 mg/300 mg of tixagevimab-cilgavimab before July 1(st), and Group C patients were up to date with the FDA dosing guidelines. RESULTS: The tixagevimab-cilgavimab group had higher incidence of stem cell transplant or CAR T-cell therapy (115/471, 24% compared to 18/126, 14% p < 0.01) and had higher vaccination status (411/471, 89% compared to 37/126, 29%, p < 0.0001). Patients that received tixagevimab-cilgavimab had a trend towards higher incidence of SARS-CoV-2 infection (70/471, 15% compared to 11/126, 9%; p = 0.08). Incidence of SARS-CoV-2 was similar amongst all dosing groups (6/21, 29% in Group A; 37/251, 15% in Group B, and 27/199, 14% in Group C, p = 0.188). Group C experienced the most infections in November and early December 2022. [Figure: see text] Group A patients received one initial dose of 150 mg/150mg of tixagevimab-cilgavimab. Group B patients received at least 300 mg/300 mg of tixagevimab-cilgavimab before July 1st, 2022 . Group C patients were up to date with the FDA dosing guidelines. CONCLUSION: The tixagevimab-cilgavimab group demonstrated increased incidence of SARS-CoV-2. This may reflect increased healthcare system utilization, as most infections were self-reported in this study. Those with the FDA recommended dose were most likely to develop SARS-CoV-2 in November and December 2022 when circulating variants were not neutralized by tixagevimab-cilgavimab in vitro. This suggests in vitro neutralization data correlates with clinical efficacy. DISCLOSURES: All Authors: No reported disclosures