P-2015. Evaluating the use of Monoclonal Antibodies - Sotrovimab, Casirivimab/Imedvimab (REGEN-COV) and Tixagevimab/Cilgavimab (EVUSHELD) for COVID-19 Treatment in Singapore
Authors: Chua Annabel , Eve Nah Puay Hoon , Hoo Grace , Hao Ying , Tay Jun Xin , Young Barnaby Edward , Toh Matthias Paul , Chen Mark , Vasoo Shawn 
Published: January 2025

Abstract

Background
The emergence of SARS-CoV-2 led to the development of therapeutic monoclonal antibodies (mAbs) including sotrovimab, casirivimab/imdevimab (REGEN-COV) and tixagevimab/cilgavimab (EVUSHELD). While tixagevimab/cilgavimab was not approved in the United States for COVID-19 treatment, there was limited off-label use in Singapore based on promising results from the TACKLE trial. The effectiveness of these mAbs against Omicron variants is uncertain.Table 1:Comparison of outcomes between patients treated with monoclonal antibody and those who did not receive monoclonal antibody treatment

Methods
This is a retrospective cohort study of hospitalized COVID-19 patients treated with mAbs from August 2021 to July 2022, who were matched with a control group at a ratio of 1:3 using propensity score matching (PSM). Characteristics used in PSM included age, gender, vaccination status, comorbidities and use of other treatment modalities ±7 days of 1st PCR positive. Firth’s Logistic regression was used to estimate the effectiveness of mAb in reducing severe COVID-19 outcomes. Patients were stratified by the years 2021 and 2022 to distinguish the Delta and Omicron variants.Table 2:Comparison of outcomes between patient receiving Sotrovimab in 2021 (Delta) and 2022 (Omicron)

Results
A total of 366 patients were treated with mAbs: 251 patients received sotrovimab, 83 tixagevimab/cilgavimab, and 32 casirivimab/imdevimab. Our analysis suggested an overall lower rate of severe COVD-19 outcome including oxygen use and composite outcomes of high flow oxygen ( &gt;4L), Intensive Care Unit (ICU) admission, or mortality when treated with mAbs (Table 1). However, these differences were not statistically significant, except for a lower oxygen use in patients treated with sotrovimab in 2022. Among 93 patients treated with sotrovimab in 2022, 91.4% did not require oxygen use compared to 81.0% not on sotrovimab (p=0.02). When comparing sotrovimab use for Omicron variant in 2022 with the Delta variant in 2021 (n=158), a lower rate of oxygen use (p&lt; 0.001) and composite outcomes (p=0.043) were observed (Table 2). Analysis between sotrovimab and tixagevimab/cilgavimab showed no significant difference in overall effectiveness.Table 3:Comparison of outcomes between patients who received Sotrovimab or Tixagevimab/Cilgavimab (EVUSHELD) in 2022

Conclusion
Despite reduced in vitro neutralization of Omicron subvariants, there was evidence of improved outcomes among patients who received Sotrovimab. Given the potential for the re-emergence of susceptibility as SARS-CoV-2 continues to evolve, mAbs may continue to serve as a valuable component of the armamentarium.

Disclosures
Barnaby Edward Young, MB BChir, PhD, Astra Zeneca: Honoraria|Gilead: Honoraria|Moderna: Honoraria|Pfizer: Honoraria|Sanofi: Grant/Research Support|Sanofi: Honoraria Shawn Vasoo, MBBS, MRCP, D(ABP), D(ABIM) (Inf Dis), FRCPath, bioMerieux: In-kind, for this study|Rosco Diagnostica: In-kind, for this study