What’s the evidence that REGEN-COV (casirivimab and imdevimab) monoclonal antibody cocktail is effective in the post-exposure prophylaxis of Covid-19?

The U.S. FDA has issued an Emergency Use Authorization (EUA) for the emergency use of REGEN-COV in adult and pediatric populations (≥12 years of age and older weighing> 40 kg) who are at high risk* of progression to severe COVID-19— including hospitalization or death— and who are not fully vaccinated or are not expected to mount an adequate immune response to the vaccine (eg, immunocompromised state).1  This recommendation is based on a randomized controlled trial involving individuals enrolled within 96 hours of exposure to a known Covid-19 case (Covid-10 Phase 3 Prevention Trial).2

In this trial, the primary efficacy end point was the development of symptomatic SARS-CoV-2 infection through day 28  in participants who did not have SARS-CoV-2 infection  by PCR or serology at the time of enrollment. Symptomatic SARS-CoV-2 infection developed in 1.5% of treatment group (vs 7.8% in placebo group) with 81.4% relative risk reduction (P<0.001); 66% reduction was observed when symptomatic and asymptomatic infections were combined.  Duration of symptoms and the magnitude and duration of detectable RNA were also lower in the REGEN-COV group compared to placebo. Therapy was well tolerated.2

In the same study, in a subgroup analysis of those who were seropositive at the time of enrollment REGEN-COV lowered the risk of symptomatic disease (0.4% vs 2.3% in the placebo group) with relative risk reduction of 81%, though not statistically significant (P=0.14).  This may be why the FDA EUA extended to certain vaccinated groups as well since to date there are no published trials on the use of REGEN-COV as post-exposure prophylaxis in vaccinated individuals.

*High risk group included ≥65 years of age, BMI≥25 kg/m2, diabetes, immunocompromised state, cardiovascular disease or hypertension, chronic lung disease, sickle cell disease and neurodevelopment disorders.

Liked this post? Download the app on your smart phone and sign up below to catch future pearls right into your inbox, all for free!

Subscribe to Blog via Email

Enter your email address to subscribe to this blog and receive notifications of new posts by email.


  1. Fact sheet for health care providers emergency use authorization (EUA) of REGEN-COV. https://www.fda.gov/media/145611/download. Accessed September 15, 2021.
  2. O’Brien MP. Forleo-Neto E, Musser BJ et al. Subcutaneous REGEN-COV antibody combination to prevent Covid-19. N Engl J Med 2021, August 4, 2021. https://www.nejm.org/doi/full/10.1056/NEJMoa2109682


Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Mercy Hospital-St. Louis, Massachusetts General Hospital, Harvard Catalyst, Harvard University, their affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

What’s the evidence that REGEN-COV (casirivimab and imdevimab) monoclonal antibody cocktail is effective in the post-exposure prophylaxis of Covid-19?

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.