Abstract Body

A previous report showed that a single 1200 mg subcutaneous (SC) dose of casirivimab and imdevimab (cas/imd) prevented symptomatic COVID-19 by 81.4% and reduced all SARS-CoV-2 infections (symptomatic and asymptomatic) by 66.4% in household contacts living with recently infected individuals over a 28-day period. While highly effective vaccines now exist for the prevention of COVID-19, a significant unmet need remains in patients who are unable to mount or maintain an adequate immune response to vaccination. Here we present additional results from 7-month follow-up period of the aforementioned study.

In this randomized, double-blind, placebo-controlled phase 3 trial, asymptomatic participants exposed to a SARS-CoV-2–infected household member were randomized 1:1 to a single SC dose of placebo or 1200 mg cas/imd (600 mg of each monoclonal antibody). Efficacy analyses include participants who were RT-qPCR negative for SARS-CoV-2 (no current infection) and seronegative for SARS-CoV-2 (no prior infection) at baseline. The trial consisted of a primary efficacy assessment period of 28 days (Month 1) and a 7-month follow-up period (Months 2–8).

Results from 842 placebo and 841 cas/imd RT-qPCR negative/seronegative enrolled participants (data through 04Oct2021, prior to emergence of Omicron) are presented. During the entirety of the 8-month study, cas/imd reduced the risk of symptomatic SARS-CoV-2 infections by 81.2% versus placebo (nominal P<0.0001; Table) and all SARS-CoV-2 infections (symptomatic and asymptomatic) by 68.2% versus placebo (nominal P<0.0001; Table). During Months 2–5, the risk of symptomatic and all infections were reduced by 100% and 89.5%, respectively (nominal P<0.0001). During Months 6–8 there was a resumption of symptomatic and all SARS-CoV-2 infections in the cas/imd group (19.9%; nominal P=0.6411 and 30.7%; nominal P=0.3967 risk reduction, respectively). Fewer cas/imd participants had a medically-attended visit versus placebo during the 8-months (1/841 [0.1%] vs 16/842 [1.9%], respectively). No new safety signals were identified for cas/imd during the follow-up period.

During the 8-month study period, a 1200 mg SC dose of cas/imd prevented SARS-CoV-2 infections, with maximal protection through Month 5. The prolonged protection supports the use of cas/imd for the long-term prevention of COVID-19 against susceptible variants, offering a pre-exposure prophylaxis strategy for individuals who are unlikely to respond or be protected by vaccination.