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FDA authorizes Covid antibody treatment as preventive after exposure

The unvaccinated or people with weak immune systems at high risk of severe disease can receive an injection if exposed to an infected person.
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People at considerable risk of developing severe Covid-19, including millions of Americans with compromised immune systems, now have the option of receiving a preventive monoclonal antibody treatment if they have been or are at risk of being exposed to the coronavirus.

The Food and Drug Administration’s action on Friday brings hope to the estimated 3 percent of Americans who are immunocompromised, including those with autoimmune diseases, HIV patients, cancer patients and organ transplant recipients, who may still be vulnerable to Covid even after being fully vaccinated.

This is the first time an injectable coronavirus antibody treatment has been approved for use as a prevention of Covid after someone has been exposed to the virus.

Dr. Myron Cohen, a leading coronavirus antibody researcher at the University of North Carolina at Chapel Hill and one of the investigators behind the study of REGEN-COV as prevention, said that monoclonal antibodies protect against severe illness by overwhelming the coronavirus infection while it is still mostly in the nose and throat.

“It’s a race between your ability to make an antibody to protect your lungs and the rest of your body and the virus,” he said. “And if you’re likely to lose the race, you’re the person for whom these antibody drugs are appropriate.”

However, the FDA said in its statement issuing the emergency expanded authorization that monoclonal antibodies should not be considered a vaccination substitute. The agency urged all who are eligible to get vaccinated.

“It’s good to know that for people who do not respond well to vaccines, including those who do not make antibodies, we can now help protect them against getting infected with SARS-CoV-2 by giving them antibodies following exposure,” said Dr. Ghady Haidar, a transplant infectious diseases physician at the University of Pittsburgh Medical Center.

Haidar is the author of a recent preprint that found that many people with cancer, organ transplants and autoimmune diseases do not produce coronavirus antibodies after receiving a Covid vaccine. While the Pittsburgh study has not been peer-reviewed, there’s growing evidence that people with weakened immune systems may not be protected after vaccination.

Monoclonal antibody treatments can help prevent severe disease, hospitalization and death. But use of the drugs has remained limited because they typically must be administered through an IV infusion and need to be given within 10 days after Covid symptoms begin.

With the FDA's expanded authorization, Regeneron’s antibody cocktail can be given as an injection. The first dose needs to be administered within 96 hours of exposure.

The FDA's expanded authorization was based on the results of a large clinical trial of the Regeneron cocktail, which contains the monoclonal antibodies casirivimab and imdevimab. The participants, who lived in the United States, Romania and Moldova, were household contacts of people who had tested positive for the coronavirus within the previous four days. They were randomly divided into two groups: one received a single injection under the skin of the Regeneron cocktail, and the other a placebo.

Among the 1,505 participants who initially tested negative for the coronavirus, 7.8 percent of the placebo group developed symptoms of Covid within four weeks, compared with just 1.5 percent of the group that received the antibody injection, an 81 percent reduction in risk. For people who did develop symptoms, the antibodies helped them clear the coronavirus faster and reduced how long their symptoms lasted.

Of the 204 participants who were infected with the coronavirus but were symptom-free when they entered the study, the antibody injection reduced their risk of developing Covid symptoms by 32 percent over the next four weeks.

No one who received the antibody injections wound up in the emergency room or was hospitalized, compared with 10 people who received the placebo.

There were only a few immunocompromised people in the study. Nevertheless, the FDA has identified members of this demographic as candidates for the preventive treatment. Others include people at high risk of exposure to infected individuals at work or in nursing homes or prisons. People who are expected to have ongoing exposure to the virus from close contacts can receive repeated doses of the antibody cocktail on a monthly basis.

Cost of the Regeneron treatment is covered by the federal government, according to a company spokesperson.

According to the FDA authorization, individuals must be unvaccinated or immunocompromised, at high risk of severe Covid, and must have been in close contact with someone who has tested positive to receive the preventive treatment.

Dr. Katharine Bar, an infectious disease specialist at the University of Pennsylvania, said the FDA authorization for prevention is reassuring for people at high risk of severe illness.

“The best defense against current infection rates is vaccinating as many people as soon as possible," said Bar, who was also an author of the Regeneron treatment as prevention. "But these highly efficacious treatment options for early infections and their contacts also have a role.”

CORRECTION: (Aug. 3, 9:30 a.m.) An earlier version of this article misstated the findings of the Regeneron clinical trial. Among participants who received the antibody injection, 1.5 percent developed symptoms of Covid, compared to 7.8 percent of the placebo group — not 7.8 percent developed symptoms, and 1.5 percent of the placebo group.