1353. Safety of AZD7442 (Tixagevimab/Cilgavimab) for Post-exposure Prophylaxis of COVID-19: Final Analysis of the STORM CHASER Phase 3 Study

Abstract Background In the STORM CHASER phase 3 post-exposure prophylaxis study, 300-mg intramuscular (IM) AZD7442 (tixagevimab/cilgavimab) reduced symptomatic COVID-19 by 33.3% vs placebo at primary analysis (P=0.212; median follow-up: 183 days) and was well tolerated. We report final safety data from STORM CHASER. Methods In STORM CHASER (NCT04625972), adults without prior SARS-CoV-2 infection or COVID-19 vaccination were enrolled within 8 days of exposure to a SARS-CoV-2–infected individual and randomized 2:1 to receive a single intramuscular dose of 300-mg AZD7442 (N=749) or placebo (N=372). Results are reported from the November 12, 2022 final data cut-off. The primary safety endpoint was assessment of adverse events (AEs), serious adverse events (SAEs), medically attended AEs (MAAEs), and AEs of special interest (AESIs). AESIs included injection site and hypersensitivity reactions. Efficacy data have previously been reported. Results Across both the AZD7442 and placebo groups, 928 (82.1%) participants completed the study. Median follow-up was 455 days (∼15 months) in both groups. AEs occurred in 46.5% and 51.9% of participants administered AZD7442 and placebo, respectively (Table). Most AEs were mild to moderate in severity; 30 (4.0%) and 26 (7.0%) of participants in the AZD7442 and placebo groups, respectively, reported an AE of grade 3 (severe) or higher. SAEs occurred in 2.7% and 4.3% of AZD7442 and placebo participants, MAAEs in 12.7% and 14.0%, AESIs in 0.5% and 1.1%, and deaths in 0.4% and 0.5%, respectively. Conclusion These findings support the long-term safety of AZD7442. Disclosures Myron J. Levin, MD, Dynavax: Advisor/Consultant|GSK: Advisor/Consultant|GSK: Grant/Research Support|GSK: Data safety monitoring/Advisory board|Johnson & Johnson: Grant/Research Support|Merck & Co.: Advisor/Consultant|Moderna: Grant/Research Support|Novavax: Grant/Research Support|Pfizer: Advisor/Consultant|Seqirus: Advisor/Consultant Andrew Ustianowski, MD, PhD, Gilead: Honoraria|Gilead: Advisory Board|GSK: Honoraria|Janssen: Honoraria|Merck: Honoraria|Merck: Advisory Board|Sanofi: Honoraria|ViiV Healthcare/GSK: Advisory Board Jesse Thissen, MSc, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Seth Seegobin, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Rohini Beavon, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Kanika Dey, MSc, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Elizabeth J. Kelly, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Karen A. Near, MD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Katie Streicher, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Alexandre Kiazand, MD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Mark T. Esser, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds