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Illustration of syringes of monoclonal antibody medication hitting a dartboard with a coronavirus germ in the middle
Credit: Tatiana Ayazo

Over the course of the pandemic, many immunocompromised patients have not been able to rejoin activities, events, and travel as fully as the general population — even if they’re fully vaccinated. That’s because people with certain underlying conditions or who take medications that affect their immune system might not mount a full response to the COVID-19 vaccine.

But now, the U.S. Food & Drug Administration (FDA) has issued an emergency use authorization (EUA) for long-acting monoclonal antibodies that can be used to prevent COVID-19 before exposure in immunocompromised individuals.

This product, AstraZeneca’s Evusheld, contains tixagevimab and cilgavimab — monoclonal antibodies that are packaged and administered together, per the FDA.

“Because immunocompromised individuals have a suboptimal response to vaccination, it is important to augment their immunity since they still remain at high risk for a severe breakthrough infection,” says infectious disease physician Amesh A. Adalja, MD, a Senior Scholar at Johns Hopkins Center for Health Security. “Long-acting monoclonal antibodies used as pre-exposure prophylaxis [prevention] can fit that need. This is something that could really protect the immunocompromised.”

Here’s everything you need to know about this new preventive treatment.

Who Can Receive Evusheld Monoclonal Antibody Injections?

Evusheld is only authorized for certain adults and children (12 years of age or older and weighing at least 40 kilograms, or about 88 pounds) who are not currently infected with the coronavirus virus and who have not recently been exposed to an infected individual, per the FDA.

It’s also only approved for those who have:

  • Moderate to severely compromised immune systems due to a medical condition or from immunosuppressive medications or treatments and may not mount an adequate immune response to COVID-19 vaccination or;
  • A history of severe adverse reactions to a COVID-19 vaccine and/or component of the vaccine, and therefore vaccination with an available COVID-19 vaccine is not recommended

Evusheld is administered as two separate consecutive injections — one per monoclonal antibody, in which one is given immediately after the other. It may be effective for pre-exposure prevention for six months.

It is not currently authorized to treat COVID-19 or for post-exposure prevention.

In a clinical trial of adults older than 59, with a pre-specified chronic medical condition, or at increased risk of SARS-CoV-2 infection for other reasons who had not received a COVID-19 vaccine (and did not have a history of SARS-CoV-2 infection), 3,441 people received Evusheld and 1,731 received a placebo, per the FDA. In the primary analysis, Evusheld recipients saw a 77 percent reduced risk of developing COVID-19 compared to those who received a placebo. The reduction in risk was maintained through six months in additional analyses.

Although this trial included unvaccinated individuals, the medication can be used by eligible high-risk patients who have been vaccinated and may not mount an adequate immune response to COVID-19 vaccination.

Possible side effects include hypersensitivity reactions such as anaphylaxis, bleeding at the injection site, headache, fatigue, and cough.

How Do Evusheld Monoclonal Antibodies Differ From Others Already Available?

Evusheld has received an emergency use authorization (EUA) to be used as a preventive tool for immunocompromised patients before exposure to COVID-19. It is given via intramuscular injection (a shot). As with other monoclonal antibody treatments, it requires 60 minutes of observation or monitoring after administration, per the U.S. Department of Health & Human Services.

On the other hand, Regeneron’s monoclonal antibody treatment includes casirivimab and imdevimab, which are administered together to prevent COVID-19 in high-risk individuals after they’ve been exposed to COVID-19. Regeneron’s two-drug cocktail has also been approved to treat mild-to-moderate COVID-19 infection in those who are at high risk for severe outcomes.

REGEN-COV can be administered either through IV administration or subcutaneous injection (a shot). While IV administration is the preferred route, subcutaneous injection may be used in situations where there would be a delay in intravenous administration.

Meanwhile, Eli Lilly and Company’s two-drug cocktail with monoclonal antibodies bamlanivimab and etesevimab is also meant to treat COVID-19 infection.  This treatment is given intravenously.

The mechanism of action among these monoclonal antibodies is similar. Some companies conducted clinical trials to show that they could use their monoclonal antibodies to prevent symptomatic COVID-19 or complications from COVID-19, while other companies conducted studies to show a therapeutic benefit of the monoclonal antibodies after someone has been diagnosed with symptomatic disease, says David Aronoff, MD, Director of the Division of Infectious Diseases at Vanderbilt University School of Medicine in Nashville, Tennessee.

“But essentially, we’re looking at the timing of administering very, very similar therapeutic or preventive monoclonal antibodies,” he says.

That said, even when they’re used as a preventive measure, monoclonal antibodies are an additional layer of protection for those who are vaccinated and high-risk — not a replacement for vaccination in those for whom it’s recommended.

How Do AstraZeneca’s Monoclonal Antibodies Work?

Monoclonal antibodies are lab-made proteins that mimic the immune system’s ability to fight off viruses and other harmful pathogens, per the FDA. Tixagevimab and cilgavimab are long-acting monoclonal antibodies meant to directly target the spike protein of SARS-CoV-2 and block the virus’ attachment to and invasion of your cells. They bind to different sites (which don’t overlap) on the spike protein of the virus.

Those antibodies can help neutralize the virus and block it from infecting the cells in your body — which can be particularly helpful for immunocompromised individuals who did not mount a full response to the COVID-19 vaccine.

“The antibodies help defend the body against getting infected and they probably help to clear the virus if someone who has received the antibodies gets infected,” says Dr. Aronoff. “And they likely help protect against the disease becoming more severe to prevent people from ending up in the hospital or dying from COVID.”

Will AstraZeneca’s Monoclonal Antibodies Work Against Omicron?

Data has yet to show if these monoclonal antibodies will be effective against highly mutated variants, such as Omicron. “What will be critical is how well the AstraZeneca monoclonal antibody cocktail holds up against the Omicron variant, if it becomes dominant,” says Dr. Adalja.

AstraZeneca’s scientists are currently testing Evusheld against the Omicron variant. They are optimistic that it will be effective against the variant, because the monoclonal antibodies target the spike protein in different but complementary ways, reports NBC News. Data are expected to be available in the upcoming weeks.

“We have seen some companies releasing data suggesting that their antibodies bind to the Omicron spike protein,” says Dr. Aronoff. “The important point here is that the technology exists to engineer antibodies that are tailor-made for particular variants if we need that. That’s an important part of our overall arsenal for reducing the burden of this infection.”

AstraZeneca’s monoclonal antibody treatment provides hope and potential flexibility to immunocompromised individuals, many of whom have felt the need to continue to follow strict mitigation efforts such as self-isolation — even if they’re fully vaccinated.

If you’re immunocompromised, talk to your health care provider (particularly one who helps treat your immunocompromising condition) about the potential availability and ability for you to receive a preventive treatment such as Evusheld.

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Coronavirus (COVID-19) Update: FDA Authorizes New Long-Acting Monoclonal Antibodies for Pre-exposure Prevention of COVID-19 in Certain Individuals. U.S. Food & Drug Administration. December 8, 2021. https://www.fda.gov/news-events/press-announcements/coronavirus-covid-19-update-fda-authorizes-new-long-acting-monoclonal-antibodies-pre-exposure.

Interview with infectious disease physician Amesh A. Adalja, MD, a Senior Scholar at Johns Hopkins Center for Health Security

Interview with David Aronoff, MD, Director of the Division of Infectious Diseases at Vanderbilt University School of Medicine in Nashville, Tennessee

Federal Response to COVID-19: Monoclonal Antibody Clinical Supplementation Guide. U.S. Department of Health & Human Services. December 16, 2021. https://www.phe.gov/emergency/events/COVID19/investigation-MCM/Documents/USG-COVID19-Tx-Playbook.pdf.

FDA clears AstraZeneca’s Covid antibody treatment for immunocompromised. NBC News. December 8, 2021. https://www.nbcnews.com/health/health-news/fda-clears-astrazenecas-covid-antibody-treatment-immunocompromised-rcna8130.