FDA Authorizes Antibody Treatment for COVID-19 Exposure

The Food and Drug Administration (FDA) has revised an emergency use authorization for the monoclonal antibody treatment REGEN-COV to include people at high risk for severe forms of COVID-19 who have had a known exposure to the virus.

REGEN-COV, which is a combination of casirivimab and imdevimab, is made by Regeneron Pharmaceuticals and was authorized for use as a post-exposure preventative treatment on August 10. The injectable and infusible prescription medication is designed for people 12 and older who weigh at least 88 pounds.

The FDA stressed that this treatment is only to be used for those who have been exposed and are at risk for developing severe COVID-19 symptoms. It is not a substitute for the COVID-19 vaccine.

“FDA has authorized three vaccines to prevent COVID-19 and serious clinical outcomes caused by COVID-19, including hospitalization and death. FDA urges you to get vaccinated, if you are eligible," the FDA said in a press release.

“This is something that makes sense,” John Sellick, DO, an infectious disease expert and professor of medicine at the University at Buffalo, tells Verywell. “When we have someone who is sick with COVID, if we get to them early enough and we give them monoclonal antibodies, it's been shown to decrease bad outcomes.”

A Phase 3 randomized, double-blind, placebo-controlled clinical trial found that there was a 62% reduction in confirmed symptomatic COVID-19 cases by day 29 in people who had the medication versus those who were given a placebo. All of the trial participants were household contacts of people who had COVID-19.

REGEN-COV was already authorized to treat mild-to-moderate COVID-19 in those 12 and up who have tested positive for SARS-CoV-2 and are at high risk for severe COVID-19.

“It’s a logical extension,” Sellick says.

What to Know about REGEN-COV

REGEN-COV uses monoclonal antibodies casirivimab and imdevimab, which are given together. Monoclonal antibodies are synthetic proteins that mimic the immune system’s ability to fight off pathogens like SARS-CoV-2, the virus that causes COVID-19.

“REGEN-COV is a combination of two engineered antibodies,” Jamie Alan, PharmD, PhD, associate professor of pharmacology and toxicology at Michigan State University, tells Verywell. “These antibodies bind to the spike protein of COVID-19, and they prevent the virus from attacking your cells and causing disease.”

There are similar medications that can be used to lower the risk of developing severe forms of COVID-19, like bamlanivimab or bamalanivimab in combination with etesevimab, Alan says.

"REGEN-COV is essentially a 'passive vaccine,'" Alan says. "With a vaccine, your body makes antibodies towards the spike protein, and your body will 'store' the information so that it can respond later when it sees the virus again. How long your body will 'store' that information is unclear. When you are exposed to COVID later after vaccination, your body will rapidly respond."

If you're unable to be vaccinated, REGEN-COV is a "great option" if you're exposed to the virus, Alan says, noting that REGEN-COV will "temporarily give your body antibodies" against COVID-19. Alan explains that these antibodies do not last long, and the body does not 'store' the information.

"Vaccination is best, but REGEN-COV is a great tool in our fight against COVID," Alan says.

How It's Administered to Patients

The FDA has very specific instructions on how REGEN-COV should be used for post-exposure preventative treatment, or prophylaxis. For dosage, patients should be given 600 milligrams of casirivimab and 600 milligrams of imdevimab together.

While an IV infusion is “strongly recommended,” the FDA says that REGEN-COV can also be given subcutaneously (under the skin) when an IV infusion isn’t feasible or would cause the patient to have a delay in treatment.

People who are still at high risk of exposure for more than four weeks and are not expected to have a full immune response to being vaccinated by COVID-19 can have initial doses of 300 milligrams of casirivimab and 300 milligrams of imdevimab together every four weeks during that exposure.

Accessibility and Limitations of REGEN-COV

REGEN-COV isn’t authorized for everyone. It may only be used in people over the age of 12 who weigh at least 88 pounds. Potential patients also must:

• Be at high risk for progression to severe COVID-19, including hospitalization or death
• Not be fully vaccinated or are not expected to have a good immune response to the COVID-19 vaccine, like people who are immunosuppressed
• Have had an exposure to an infected person that meets the CDC's criteria as a “close contact” (within six feet of someone for 15 minutes or more over a 24-hour period), or who are at an increased risk of exposure because of high infection rates where they live or work, such as a nursing home or prison.

Known Side Effects

There are a few potential side effects of REGEN-COV. They’re largely injection site reactions, including:

• Skin redness
• An uncomfortable, irritating sensation that creates an urge to scratch
• Discoloration of the skin

Antihistamines, hydrocortisone cream, and ice should help with the symptoms, Alan says. There were no cases of severe hypersensitivity reactions or potentially life-threatening allergic reactions.

How to Get REGEN-COV After Being Exposed to COVID-19

If you are at high risk for developing severe complications of COVID-19 and you have a known exposure, call your doctor. They should be able to discuss whether REGEN-COV is the appropriate treatment for you. The U.S. government has covered the cost of the first 1.5 million doses of REGEN-COV so those who need the treatment can get it for free. But patients or their insurance providers may have to pay some other administration fees.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.