LAUSR

Background: Pre-exposure prophylaxis for COVID-19 with tixagevimab/cilgavimab (T/C) received Emergency Use Authorization (EUA) based off of results from a clinical trial conducted prior to the Omicron variant. Its clinical effectiveness has not been well described in the Omicron era. We examined the incidence of symptomatic illness and hospitalizations among T/C recipients when Omicron accounted for virtually all cases. Methods: We used the electronic medical record to identify patients who received T/C at our institution. Among these patients, we assessed for cases of symptomatic COVID-19 and associated hospitalizations before and after receiving T/C. We used chi square tests and Fishers exact p-values to examine differences between characteristics of those who got COVID before and after T/C prophylaxis. Results: Of 1295 T/C recipients, 121 (9.3%) developed symptomatic COVID-19 before receiving T/C, and 102 (7.9%) developed symptomatic disease after receiving it. Among those with infection prior to T/C, 36/121 (29.8%) were hospitalized, including 8 (6.6%) admitted to the ICU. Among those with COVID-19 after receiving T/C, 6/102 (5.9%) were hospitalized but none required ICU admission. No COVID-related deaths occurred in either group. The majority of COVID-19 cases among those infected prior to T/C treatment occurred during Omicron BA.1 surge, while the majority of cases among post-T/C recipients occurred when BA.5 was predominant. Patients infected with COVID-19 prior to receiving T/C had received fewer vaccine doses and were less likely to receive COVID-19 therapeutics compared to those with COVID-19 after having received T/C. Conclusion: We identified COVID-19 infections after T/C prophylaxis. Among persons eligible for T/C, COVID-19 illnesses occurring after T/C were less likely to require hospitalization compared to those with COVID-19 prior to T/C. In the presence of changing vaccine coverage, multiple therapies, and changing variants, the effectiveness of T/C in the Omicron era remains difficult to assess.