Introduction: The clinical evidence for combination therapy with casirivimab plus imdevimab (REGN-COV2) consists of a published RCT with an adaptive study design (part of the patient population from phase 1/2) with preliminary results from 275 patients with mild to moderate SARS-CoV2 disease and the unpublished phase 3 part of the same RCT in 4,567 non-hospitalised high-risk adults with mild to moderate SARS-CoV2 disease.

Clinical efficacy: In the interim results of the RCT (low confidence in evidence) of the combination of casirivimab and imdevimab (REGN-COV2) in 275 non-hospitalised COVID-19 patients with mild-to-moderate disease, no deaths were reported, whereas treatment with REGN-COV2 reduced both viral load and the number of medical visits. Based on the unpublished final results of the phase 3 part of the same RCT conducted in 4,567 patients, the combination of casirivimab and imdevimab (REGN-COV2) significantly reduced the risk of hospitalisation or death by 70% (1200 mg intravenously) and 71% (2400 mg intravenously) compared to placebo.

Safety: The interim results of the RCT do not indicate whether REGN-COV2 leads to an increase in adverse events (AEs) and/or serious adverse events (SAEs) compared with placebo. The same is true for REGN-COV2 at other doses. No new safety signals were identified in the unpublished final results from the phase 3 part of the same RCT either. Serious adverse events were mostly related to COVID-19.

Conclusion: The unpublished results must be interpreted with caution until a peer-reviewed publication is available. A final assessment is not possible based on the current data.