1. Close household contacts of SARS-CoV-2-infected individuals, who were asymptomatic and positive on RT-qPCR, had a significantly reduced risk of progression to symptomatic infection if treated with subcutaneous casirivimab and imdevimab compared to placebo.
2. The length of high viral load and duration of symptoms among those who became symptomatic were significantly reduced among casirivimab and imdevimab-treated participants.
Evidence Rating Level: 1 (Excellent)
Study Rundown: There is high demand during the COVID-19 pandemic to discover ways of slowing the spread and reducing infection rates. Casirivimab and imdevimab are monoclonal antibodies that bind the SARS-CoV-2 spike protein and prevent the entry of the virus into the body. This phase 3 randomized clinical trial investigated whether subcutaneous casirivimab and imdevimab can reduce progression to symptomatic SARS-CoV-2 infection among baseline asymptomatic close household contacts of infected individuals. This trial was conducted between July 13, 2020, and January 28, 2021, at 112 United States sites. Participants were randomized to receive one dose of casirivimab and imdevimab (n= 158) or placebo (n= 156) within 96 hours of the infected individual’s positive SARS-CoV-2 test. The primary outcome was the proportion of close contact participants who had a positive RT-qPCR result at baseline or within 28 days and developed signs and symptoms of COVID-19 within 14 days of the positive test result. Subcutaneous casirivimab and imdevimab significantly reduced the risk of symptomatic infection within 14 days of a positive RT-qPCR test compared to placebo (29/100 [29.0%] vs. 44/104 [42.3%]; odds ratio [OR]: 0.54 [95% CI: 0.30-0.97]; p= 0.04). Among symptomatic participants, the duration of symptoms was reduced by an average of 5.6 days in the treatment group compared to placebo (21.7 days vs 27.3 days; p= 0.03). Furthermore, the number of weeks with a high viral load (defined as >4 log10 copies/mL) in nasopharyngeal swab samples was significantly reduced among treated patients (489.6 weeks vs. 811.9 weeks per 1000 participants; p= 0.001). Overall, subcutaneous treatment with casirivimab and imdevimab demonstrated significantly reduced progression to symptomatic SARS-CoV-2 infection among asymptomatic, infected, close household contacts. Notably, this trial was conducted before widespread vaccination and onset of variants, such as Delta and Omicron; therefore, further studies are required to elucidate whether these results are consistent during different phases of the pandemic.
Relevant Reading: Subcutaneous REGEN-COV antibody combination to prevent COVID-19
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