Monoclonal Antibodies for COVID-19

The recent surge in COVID-19 cases has heightened interest in the use of monoclonal antibodies to treat and prevent the infection, particularly in unvaccinated patients (B. Mueller. Shunning shots but lining up for antibodies. NY Times, Sept 19, 2021, p. 1). Three monoclonal antibody products are available in the US: casirivimab and imdevimab (REGEN-COV – Regeneron), bamlanivimab and etesevimab (Lilly), and sotrovimab (GSK). All have received Emergency Use Authorizations (EUAs) for treatment of patients ≥12 years old and weighing ≥40 kilograms with mild to moderate COVID-19 infection at high risk of progressing to severe COVID-19 and hospitalization.

Casirivimab and imdevimab and bamlanivimab and etesivimab have had their EUAs expanded to allow use for post-exposure prophylaxis in persons who are not fully vaccinated against COVID-19 or are unlikely to have an adequate immune response to full vaccination and have been in close contact with a SARS-CoV-2-infected individual or are likely to be exposed to SARS-CoV-2 in the setting of an institutional outbreak and are at high risk of progression to severe COVID disease or hospitalization (Med Lett Drugs Ther, August 23, 2021).

Which conditions put patients at high risk for severe COVID disease? The FDA has made a list, which appears below:

All three of the available monoclonal antibody products can be administered as an IV infusion, but that can be difficult logistically, especially in settings where IV infusion rooms are populated mainly by immunocompromised patients. Casirivimab and imdevimab can also be given in 4 consecutive 2.5-mL subcutaneous injections, which presumably can be given in more accessible healthcare settings.

Casirivimab and imdevimab (REGEN-COV) and sotrovimab are authorized for use in all states, territories, and US jurisdictions. Based on in vitro assays, they are considered likely to retain activity against the P.1 (Gamma), B.1.351 (Beta), B.1.617.2 (Delta), AY.1 and AY.2 (Delta plus), and  B.1.621 variants. Bamlanivimab and etesevimab, on the other hand, were not expected to retain activity against the non-Delta variants and were removed from distribution in late June. By late August, however, Delta variants constituted 99% of isolates, and distribution of bamlanivumab and etesivimab was resumed.

On September 3rd, the NIH made recommendations on how to prioritize monoclonal antibodies if there were logistical problems in their supply or administration, principally by not offering them to healthy vaccinated patients, especially for post-exposure prophylaxis ( At the time, there was no shortage of monoclonal antibodies, but now there is, and states are beginning to recommend restriction of the limited supply to the unvaccinated. Many in the public and healthcare community are angry that unvaccinated patients are again taking advantage of limited COVID resources.

Monoclonal antibodies interfere with viral replication. They should be given as soon as possible after a positive SARS-CoV-2 test result and within 10 days (preferably earlier) of onset of symptoms. They are not recommended for use in patients hospitalized for COVID-19 or in any patients who require oxygen therapy because of COVID-19.

Extensive information about these 3 products, their efficacy and adverse effects, can be found in the Drugs for COVID-19 table (free) on our web site.

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  1. It’s getting difficult to decide where the behavioral economic line of stupidity has been crossed. I suspect it is far less expensive to immunize, yet certain GOP voters and governors have resisted mightily.

  2. Barry Gloger, MD, FAAOS says:

    All treatment, including Monoclonal Antibodies and Hospitalization, should be denied to voluntary non vaccinators.

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