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Casirivimab–Imdevimab reduced hospitalisation of high-risk patients with mild to moderate COVID-19

Among high-risk patients with mild to moderate COVID-19, casirivimab–imdevimab treatment was associated with a significantly lower rate of hospitalisation, reports a Mayo Clinic study in The Lancet’s EClinicalMedicine.

The two monoclonal antibody treatments have been approved for emergency use by the US Food and Drug Administration.

Nearly 1,400 Mayo Clinic patients were enrolled in the study, 696 who received the drug combo between December 2020 and early April and an equal matched cohort who did not receive it. Their status was evaluated at 14, 21 and 28 days after treatment. At each point, the numbers for hospitalisation were significantly lower in the treated group.

At Day 14, 1.3% of the treated group was in the hospital, compared with 3.3% of those who had not been treated. At Day 21, only 1.3% treated was hospitalised, compared to 4.2% of those who had not been treated. At the end of 28 days, 1.6% of those treated were hospitalised versus 4.8% of those who had not been treated. This translated to 60%-70% relative reduction in hospitalisation among treated patients. Of those who were subsequently hospitalised, the rates of ICU admission and mortality were low.

"Once again, this real-world study suggests that when patients who are at high risk due to a range of comorbidities contract a mild or moderate case of COVID-19, this combination of monoclonal injections gives them a chance of a non-hospitalised recovery. In other words, they recover safely at home," says Dr Raymund Razonable, a Mayo Clinic infectious diseases specialist and senior author of the study.

In a previous Mayo Clinic study published in The Journal of Clinical Investigation, findings suggested the use of bamlanivimab reduced hospitalisations in high-risk patients by 40%-60%. That study involved 2,335 treated patients from Mayo Clinic between November of 2020 and February 2021.

Comparing their outcomes with 2,335 untreated patients, the ICU admission and mortality rates also were significantly lower with monoclonal antibody treatment. It should be noted that the FDA in April revoked the EUA for bamlanivimab alone and now endorses use of combination monoclonal antibodies.

"Our conclusion overall at this point is that monoclonal antibodies are an important option in treatment to reduce the impact of COVID-19 in high- risk patients," says Razonable.

Study details

Raymund R. Razonable, Colin Pawlowski, John C. O'Horo, Lori L. Arndt, Richard Arndt, Dennis M. Bierle, Molly Destro Borgen, Sara N. Hanson, Michelle C. Hedin, Patrick Lenehan, Arjun Puranik, Maria T Seville, Leigh L. Speicher, Sidna M. Tulledge-Scheitel, AJ Venkatakrishnan, Caroline G. Wilker, Andrew D. Badley, Ravindra Ganesh.

Published in EclinicalMedicine 30 August 2021


Real-world clinical data to support the use of casirivimab–imdevimab for the treatment of outpatients with mild to moderate coronavirus disease-19 (COVID-19) is needed. This study aimed to assess the outcomes of casirivimab–imdevimab treatment of mild to moderate COVID-19.

A retrospective cohort of 696 patients who received casirivimab–imdevimab between December 4, 2020 and April 9, 2021 was compared to a propensity-matched control of 696 untreated patients with mild to moderate COVID-19 at Mayo Clinic sites in Arizona, Florida, Minnesota, and Wisconsin. Primary outcome was rate of hospitalization at days 14, 21 and 28 after infusion.

The median age of the antibody-treated cohort was 63 years (interquartile range, 52–71); 45·5% were ≥65 years old; 51.4% were female. High-risk characteristics were hypertension (52.4%), body mass index ≥35 (31.0%), diabetes mellitus (24.6%), chronic lung disease (22.1%), chronic renal disease (11.4%), congestive heart failure (6.6%), and compromised immune function (6.7%).

Compared to the propensity-matched untreated control, patients who received casirivimab–imdevimab had significantly lower all-cause hospitalization rates at day 14 (1.3% vs 3.3%; Absolute Difference: 2.0%; 95% confidence interval (CI): 0.5–3.7%), day 21 (1.3% vs 4.2%; Absolute Difference: 2.9%; 95% CI: 1.2–4.7%), and day 28 (1.6% vs 4.8%; Absolute Difference: 3.2%; 95% CI: 1.4–5.1%). Rates of intensive care unit admission and mortality at days 14, 21 and 28 were similarly low for antibody-treated and untreated groups.

Among high-risk patients with mild to moderate COVID-19, casirivimab–imdevimab treatment was associated with a significantly lower rate of hospitalisation.


The Lancet article – Casirivimab–Imdevimab treatment is associated with reduced rates of hospitalization among high-risk patients with mild to moderate coronavirus disease-19.


See more from MedicalBrief archives:


FDA expands emergency use of REGEN-COVTM (casirivimab and imdevimab)


At last, serious efforts to repurpose generic drugs to treat COVID-19


Injected antibody cocktail cuts COVID-19 infection risk by over 80%


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