Clinical Prognosis of Patients With Mild COVID-19 Treated With Casirivimab/Imdevimab in Japan

Aim: This study aimed to report clinical courses of patients who had mild coronavirus disease 2019 (COVID-19), defined as SpO(2) of 96 or higher, and treated with/without casirivimab/imdevimab in Japan, where mortality and number of severe patients were very limited compared to other resource-rich countries. Methods: We conducted a retrospective cohort study in Toyota Regional Medical Center, Toyota, Japan, from August 31, 2021, to September 27, 2021. We included all patients with COVID-19 who were diagnosed at the hospital’s family medicine department. Our primary outcome was admission to the hospital due to COVID-19 and secondary outcome was mortality due to COVID-19. We compared those who received casirivimab/imdevimab and those who did not. Results: A total of 104 patients were included, of whom 30 received casirivimab/imdevimab and 74 did not receive casirivimab/imdevimab. The mean age of the patients was 47.8 ± 15.6 (standard deviation {SD}) years, 57 (54.8%) patients were male. During a median follow-up period of 12 days (interquartile range: 10-16 days), 19 (18.3%) patients were admitted to the hospital and none died. Patients who received casirivimab/imdevimab had similar rate to admission (p = 0.87). The hazard ratio (HR) of admission tended to be lower for those who received casirivimab/imdevimab (HR: 0.76, 95% confidence interval {CI}: 0.23-2.49, p-value = 0.65), but not statistically significant compared to those who did not, after adjusting for age, gender, risk factors, including obesity. Conclusions: Our study demonstrated that patients with COVID-19 had similar disease progression rates regardless of casirivimab/imdevimab administration.