Should patients previously immunized against Covid-19 receive selected monoclonal antibodies when diagnosed with a breakthrough infection?

Although published studies supporting monoclonal antibody therapy in mild to moderate Covid-19 preceded availability of Covid-19 vaccines and the emergence of new variants of concern,1,2 given the possibility of severe breakthrough Covid-19 in high risk vaccinated patients with suboptimal immunity and the retained activity of certain monoclonal antibody products (ie, casirivimab and imdevimab-Regeneron-Cov and sotrovimab) against common variants of SARS-CoV-2 , their use is recommended even in vaccinated individuals with mild to moderate Covid-19.3-5

In fact, the CDC states that “For people who have received one or more doses of Covid-19 vaccine and subsequently experience SARS-CoV-2 infection, prior receipt of a Covid-19 vaccine should not affect treatment decisions (including use of monoclonal antibodies, convalescent plasma, antiviral treatment, or corticosteroid administration) or timing of such treatment.”3

In its July 30, 2021 Emergency Authorization Use (EUA) letter regarding use of casirivimab and imdevimab – REGEN-COV), the FDA does not distinguish between vaccinated and unvaccinated individuals for its indications,4 similar to those of guidelines posted by the Department of Health and Human Services and the NIH.5-6

When indicated, high risk vaccinated individuals with Covid-19 should be offered  an FDA approved (under EUA currently) monoclonal antibody product (such as  casirivimab and imdevimab antibody cocktail or sotrovimab) soon after diagnosis and certainly no later than 10 days.

Vaccinated individuals with mild to moderate Covid-19 not requiring hospitalization and for whom monoclonal antibody treatment may be indicated include older patients and those with risk factors for severe disease, such as obesity, pregnancy, chronic kidney disease, chronic lung disease (including COPD), immunocompromised state, serious heart conditions (eg, heart failure, coronary artery disease, cardiomyopathies), sickle cell disease and type 2 diabetes.7

Of note, casirivimab and imdevimab is indicated for adults (weighing at least 40 kg) and children 12 years or older and is administered by IV infusion or subcutaneously, if IV infusion is not feasible and would lead to delay in treatment.4

Bonus Pearl: Did you know that in phase III trials, casirivimab and imdevimab  antibody cocktail reduced hospitalization or death by 70% in non-hospitalized patients with Covid-19?2

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  1. Interim clinical considerations for use of Covid-19 vaccines currently authorized in the United States. 2021. Available at Accessed August 22, 2021.
  2. March 23, 2021
  3. Dougan M, Nirula A, Azizad M, et al. Bamlanivimab plus Etesevimab in mild or moderate Covid-19. N Engl J Med, July 14, 2021.
  4. Letter, EUA REGEN-COV, July 30, 2021.
  5. Department of Health and Human Services. High risk Covid-19 outpatients may avoid hospitalization with monoclonal antibody treatment. July 16, 2021.
  6. Anti-SARS Cov-2 monoclonal antibodies. Accessed August 22, 2021.
  7. Science brief: evidence used to update the list of underlying medical conditions that increase a person’s risk of severe illness from Covid-19. Accessed August 22, 2021.

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Mercy-St. Louis, Massachusetts General Hospital, Harvard Catalyst, Harvard University, their affiliate 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!

Should patients previously immunized against Covid-19 receive selected monoclonal antibodies when diagnosed with a breakthrough infection?

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