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A photo of a doctor holding a vial of monoclonal antibodies, a new treatment for coronavirus Covid-19.
Credit: Cristian Storto Fotografia/iStock

Immunocompromised people now have another tool to help prevent a COVID-19 infection: monoclonal antibody treatment.

The U.S. Food & Drug Administration (FDA) has authorized the use of REGEN-COV, a monoclonal antibody treatment, to prevent COVID-19 in adults and children (age 12 and older, who weigh at least 88 pounds) who are at high risk for progression to severe COVID-19 — including hospitalization or death. The treatment, however, can only be issued after a person has been exposed to the coronavirus. (This means you can’t take it without knowing you’ve been exposed to the virus, say, because a close contact, such as someone in your household, has become infected.)

Monoclonal antibodies are proteins made in a lab that mimic the immune system’s ability to ward off viruses like SARS-CoV-2, according to the FDA. Monoclonal antibodies may block the virus from adhering to your cells and help neutralize it, making it more difficult for the virus to replicate and spread.

Exposure to an infected person is key in this authorization: You cannot get REGEN-COV to prevent COVID-19 if you haven’t been exposed to the SARS-CoV-2 virus. Also keep in mind that monoclonal antibody treatment is not meant to replace the COVID-19 vaccine.

“Vaccines are the mainstay of prevention,” says Myron Cohen, MD, a coronavirus antibody researcher at the University of North Carolina at Chapel Hill who has studied the use of REGEN-COV as prevention. “Of course, it is often hard to recognize exposure since asymptomatic people can be contagious, even if vaccinated.”

In other words, one of the many reasons getting the COVID-19 vaccine is important is because you don’t always know when you’ve been exposed to COVID-19 (and therefore, when you should receive monoclonal antibody treatment if you’re at high risk).

For people who are immunocompromised because they take immunosuppressant medication, monoclonal antibody treatment can cover your bases if you know you’ve been exposed but may not have mounted a full immune response to the vaccine.

The FDA notes that this authorization applies to those who are:

  • At high risk for progression to severe COVID-19, including hospitalization or death, and
  • Not fully vaccinated or not expected to mount an adequate immune response to complete SARS-CoV-2 vaccination (for example, people with immunocompromising conditions, including those taking immunosuppressive medications), and
    • Have been exposed to an individual infected with SARS-CoV-2 consistent with close contact criteria per Centers for Disease Control and Prevention (CDC), or
    • Who are at high risk of exposure to an individual infected with SARS-CoV-2 because of occurrence of SARS-CoV-2 infection in other individuals in the same institutional setting (for example, nursing homes or prisons)

You’re considered fully vaccinated if it’s been two weeks since you received the second dose of the Pfizer of Moderna vaccines or the single dose of the Johnson & Johnson vaccine.

Meanwhile, close contact means you’ve been within six feet of an infected person for a cumulative total of 15 minutes or more within a 24-hour period, according to the U.S. Centers for Disease Control and Prevention.

“Monoclonal antibodies are suited to hosts [who are] unlikely to respond to vaccines,” says Dr. Cohen. This, he notes, includes people with diseases and undergoing treatments that compromise B cells, such as rituximab.

B cells are key players in regulating your immune response, according to the British Society for Immunology, as they produce antibodies needed to fight viruses. Sometimes, however, they can cause inflammation, autoantibodies, and other issues in people with certain conditions, making them an important therapeutic target in autoimmune diseases, some cancers, and transplantation. Medications like rituximab deplete B cells, which can make you more prone to infection.

REGEN-COV is already authorized to treat mild-to-moderate COVID-19 — after being infected — in those who are at high risk for severe outcomes. It is made with the monoclonal antibodies casirivimab and imdevimab (600 milligrams each, administered together). Although IV administration is strongly recommended for treating COVID-19, either IV administration or an injection is appropriate for preventing COVID-19 after exposure.

If you remain at high risk of exposure to someone with COVID-19 for more than four weeks, and you’re not expected to mount an adequate immune response to the vaccine, repeat doses of 300 milligrams of casirivimab and 300 milligrams of imdevimab every four weeks for the duration of the ongoing exposure may be administered, according to the FDA.

Keep in mind that the sooner you get monoclonal antibodies after you’re exposed or infected, the more effective they may be. Dr. Cohen says that after exposure to an infected individual, you should be treated with monoclonal antibodies (if eligible) as soon as possible — and within 96 hours.

“This is a race against viral replication,” he says.

The FDA based its recommendation on data from a Phase 3 clinical trial that was randomized, double-blind, and placebo-controlled. Researchers studied a single dose of REGEN-COV for COVID-19 prevention in household contacts of individuals infected with SARS-CoV-2.

REGEN-COV treatment was associated with an 81 percent reduction in confirmed symptomatic COVID-19 compared to a placebo after four weeks in the primary analysis population (1,505 participants who tested negative for coronavirus at baseline). For those who developed symptoms, monoclonal antibody treatment helped them recover faster and reduced the duration of their symptoms. In fact, individuals treated with REGEN-COV resolved their symptoms in one week on average compared to three weeks in the placebo group. Nobody who received monoclonal antibody treatment ended up in the hospital or emergency room, compared to four people in the placebo group.

Among the participants enrolled in this prevention trial, 31 percent had at least one known factor that made them high-risk for severe consequences from COVID-19. Injection site reactions were the most common side effects. There were no cases of severe hypersensitivity reactions or potentially life-threatening allergic reactions.

You can find medical centers that have received shipments of monoclonal antibody therapeutics within the past several weeks by visiting the U.S. Department of Health & Human Services.

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Appendices. COVID-19. U.S. Centers for Disease Control and Prevention. August 3, 2021. https://www.cdc.gov/coronavirus/2019-ncov/php/contact-tracing/contact-tracing-plan/appendix.html.

COVID-19 Frequently Asked Questions. U.S. Food & Drug Administration. July 30, 2021. https://www.fda.gov/emergency-preparedness-and-response/coronavirus-disease-2019-covid-19/covid-19-frequently-asked-questions.

B-cell mediated disease. British Society for Immunology. Accessed August 11, 2021. https://www.immunology.org/public-information/bitesized-immunology/immune-dysfunction/b-cell-mediated-disease.

Interview with Myron Cohen, MD, a coronavirus antibody researcher at the University of North Carolina at Chapel Hill

Phase 3 Prevention Trial Showed 81% Reduced Risk of Symptomatic SARS-CoV-2 Infections with Subcutaneous Administration of REGEN-COV™ (casirivimab with imdevimab). Cision PR Newswire. April 12, 2021. https://www.prnewswire.com/news-releases/phase-3-prevention-trial-showed-81-reduced-risk-of-symptomatic-sars-cov-2-infections-with-subcutaneous-administration-of-regen-cov-casirivimab-with-imdevimab-301266366.html.