Monoclonal Antibodies for Post Exposure Prophylaxis of COVID-19 A Crash Course & Update

by Mary O’Brien, M.D.


Monoclonal Antibodies (mAB’s) are a form of immunotherapy, manufactured in vitro to target specific antigens. A wide array of mAB’s are used to treat malignancies such as breast, lung, colon, and renal cell cancer, melanoma, multiple myeloma, lymphomas, and leukemia.

Monoclonal antibodies are also used in the treatment of inflammatory autoimmune disorders such Crohn’s Disease, MS, rheumatoid arthritis, psoriatic arthritis, and ankylosing spondylitis. These mAB’s can be directed against such targets as specific B cells, T cells, tumor necrosis factor-alpha (TNF-α) interleukins, cytokines, various proteins, and receptor sites on cells

Commonly used drugs such as Humira (adalimumab) and Remicade (infliximab) are mAB’s.


Since late 2020, a combination of the mAB’s casirivimab and imdevimab, known as REGEN-COV, has had Emergency Use Authorization (EUA) for patients ≥12 years with mild to moderate COVID and a high risk of progression to severe disease or hospitalization. People in the media and others have referred to this as “Regeneron,” since few people can pronounce or remember the actual mAB combination. “Regeneron” is not a drug, it’s the name of the pharma company that makes the drug.

Last week, the FDA expanded this EUA for use as post-exposure prophylaxis of COVID if:

  • The patient is not fully vaccinated (and at high risk) or
  • The patient is unlikely to have an adequate immune response to full vaccination and has been in close contact with a COVID infected person or is likely to be exposed to COVID in an institutional setting (nursing home, military barracks, prison, etc.)


The protocol for REGEN-COV as post-exposure prophylaxis is:

  • Casirivimab 600 mg plus
  • Imdevimab 600 mg

This can be given as either four consecutive shots (SC injections) at one time or as a single IV infusion Either route of administration is fine. There is no preference.

This combination of monoclonal antibodies has retained effectiveness against all COVID variants, including Delta, as of 8/23/2021.

Updated FDA Criteria for High Risk Conditions for COVID-19 Progression (May 2021)

  • Age 65 or older
  • BMI ≥25 (overweight or obese)
  • Pregnancy
  • Chronic kidney disease
  • Diabetes
  • Cardiovascular disease
  • Hypertension
  • COPD, moderate to severe asthma, or other chronic respiratory disease
  • Current treatment with immunosuppressive therapy
  • Sickle cell disease
  • Congenital or acquired heart disease
  • Neurodevelopmental disorders (such as cerebral palsy or Down syndrome), or other conditions that confer medical complexity
  • A medical-related technological dependence (such as tracheostomy or gastrostomy)
  • Patients 12 years or older with an overweight BMI, pregnancy, cardiovascular disease, hypertension, or chronic respiratory disease are now considered high risk

Vaccination against COVID-19 is prudent for the vast majority of people, But dealing with COVID is far more complex than screaming at everyone to wear masks and “get the jab.” The age, underlying medical conditions, and living, schooling, or working conditions of the individual patient matter.

Stay tuned. It’s not over yet.