Monthly treatment with subcutaneous casirivimab/imdevimab was well tolerated and associated with significant protection against COVID-19, according to results of a phase 1, double-blinded, placebo-controlled trial published in the International Journal of Infectious Diseases.

In this study, researchers assessed the safety, tolerability, and efficacy of monthly subcutaneous injections of casirivimab/imdevimab for the prevention of SARS-CoV-2 infection in uninfected adults (age range, 18-90 years).

Patients were randomly assigned in a 3:1 fashion to receive either subcutaneous casirivimab/imdevimab (1200 mg) or placebo every 4 weeks for up to 24 weeks.

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The primary endpoints included the incidence of adverse events (AEs) of special interest within 4 days of treatment administration and serum concentrations of casirivimab/imdevimab over time. The rate of treatment-emergent AEs and immunogenicity were secondary endpoints, with immunogenicity determined via measurement of anti-drug antibodies (ADAs) against casirivimab/imdevimab.

There were 969 patients included in the study, of whom 729 received casirivimab/imdevimab and 240 received placebo. Overall, the mean age was 48 years, 44.9% were women, 10% were Black, and 23.4% were Hispanic.

The incidence of SARS-CoV-2 infection during the study period was lower in the intervention group than in the placebo group (0.4% vs 5.4%; odds ratio, 0.07; 95% CI, 0.01-0.27; nominal P <.001), indicating that casirivimab/imdevimab was associated with a relative risk reduction of 92.4%.

Among 3 (0.4%) patients in the casirivimab/imdevimab group who reported SARS-CoV-2 infection as an AE, all were seronegative for SARS-CoV-2 antibodies at baseline and at the end of treatment and none had laboratory-confirmed SARS-CoV-2 infection.

No AEs of special interest or deaths were reported during the 6-month treatment period. The rate of severe treatment-related AEs was similar between the casiribimab/imdevimab group and the placebo group (0.7% vs 0.8%). Injection site reactions occurred among 266 (36.5%) and 40 (16.7%) patients in the casirivimab/imdevimab and placebo groups, respectively. All injection site reactions were of mild or moderate severity, with the majority (>60%) resolving within 4 days of treatment administration.

Both casirivimab and imdevimab were associated with low treatment-emergent immunogenicity, with ADAs measured in 5% or less of the study population.

This study was limited by the lack of regular reverse transcription polymerase chain reacting testing among patients who developed symptoms suggestive of COVID-19. In addition, the researchers were unable to assess the effect of nonpharmaceutical interventions on SARS-CoV-2 transmission, such as the use of personal protective equipment and social distancing.

According to the researchers, “…the efficacy and safety profile of [casirivimab/imdevimab] demonstrated in this study strongly support that [it] could be used for COVID-19 prophylaxis in individuals not expected to mount a sufficient immune response to vaccination when circulating variants are susceptible to [casirivimab/imdevimab].”

Disclosure: Some authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.


Isa F, Forleo-Neto E, Meyer J, et al. Repeat subcutaneous administration of casirivimab and imdevimab in adults is well-tolerated and prevents the occurrence of COVID-19. Int J Infect Dis. Published online July 1, 2022. doi:10.1016/j.ijid.2022.06.045

This article originally appeared on Infectious Disease Advisor