Effectiveness of Severe Acute Respiratory Syndrome Coronavirus 2 Monoclonal Antibody Infusions in High-Risk Outpatients.

BACKGROUND: Coronavirus disease 2019 (COVID-19) continues to stress the health care system. Neutralizing monoclonal antibodies (mAbs) were effective in reducing COVID-19-related hospitalizations and emergency department (ED) visits in their respective clinical trials. However, these results have yet to be reproduced in a practical setting following implementation of current US Food and Drug Administration (FDA) guidance. METHODS: This retrospective cohort study included outpatients with confirmed COVID-19 infection, who had mild/moderate symptoms for 10 days or less, and who were deemed high-risk for severe COVID-19 under FDA's Emergency Use Authorization for mAbs. Patients who received either bamlanivimab or casirivimab/imdevimab from 18 November 2020 through 5 January 2021 were included (n = 200). This was compared against a control cohort of randomly selected high-risk COVID-19 outpatients who declined or were not referred for mAb treatment during the same period (n = 200). The primary outcome was a composite of 29-day COVID-19-related hospitalizations and/or ED visits. Prespecified secondary outcomes included the individual components of the primary endpoint, 29-day all-cause mortality, and serious adverse drug events. RESULTS: Patients treated with mAbs were significantly less likely to be hospitalized or visit the ED compared with patients not treated with mAb (13.5% vs 40.5%; odds ratio, 0.23 [95% confidence interval, .14-.38]; P < .001). The mortality rate was 0% in the mAb group compared with 3.5% in the control group (P = .02). Only 2 patients receiving mAb experienced a serious adverse event requiring treatment. CONCLUSIONS: Among high-risk COVID-19 outpatients with mild/moderate symptoms, early administration of mAbs can potentially reduce the strain on the health care system during the current pandemic.