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Monoclonal Antibodies: A New Treatment for Long COVID?

Hallie Levine

A treatment used to treat acute COVID-19 infection has also been found to be effective against long COVID, a new small study has found. The research, which assessed the benefits of monoclonal antibodies, suggests relief may finally be ahead for millions of Americans with long COVID for whom treatment has remained elusive.

The study, published in the American Journal of Emergency Medicine, found three Florida patients with long COVID made complete — and sudden — recoveries after they were given the monoclonal antibody cocktail casirivimab/imdevimab (Regeneron).

"We were struck by how rapid and complete the remissions were," said study coauthor Paul Pepe, MD, MPH, a professor of management, policy and community health at the School of Public Health at the University of Texas Health Sciences Center. "We found that no matter how long the patients were sick for — whether it was 5, 8, or 18 months — within 5 days, they appeared to be completely cured."

All three patients had been initially infected with COVID-19 early in the pandemic, in 2020 or the first half of 2021. They were given Regeneron either after a reinfection or exposure to COVID-19, as a preventative, at state-run COVID clinics in Florida.

"In each case, the infusions were given to help prevent their long COVID from worsening," said Pepe.

The researchers collected medical histories for all three patients, asking about symptoms such as physical fatigue, exercise intolerance, chest pain, heart palpitations, shortness of breath, cognitive fatigue, and memory problems. They asked patients to rate symptoms pre-COVID (baseline), during the long COVID phase, post-vaccine, and finally a week after their monoclonal antibody treatment. They also interviewed family members.

They found that across the board, symptoms improved significantly and often completely vanished. Their loved ones corroborated these reports as well.

One of the patients, a 63-year-old Floridian woman, came down with a mild case of COVID-19 at the start of the pandemic in March 2020 that lasted about 2 weeks. But several weeks later, she developed extreme, debilitating fatigue, along with chest pain and shortness of breath.

"I was chasing my 6-pound Yorkie one day after she got loose, and I was struck with such intense chest pain I fell down,” the woman said in an interview with Medscape Medical News, asking not to be identified.

Her symptoms progressed to the point where she no longer felt safe babysitting her grandchildren or driving to the grocery store.

"My short-term memory was completely gone. I couldn't even read more than a paragraph at a time," she said.

When she was exposed to COVID-19 in October 2021, her doctor suggested Regeneron as a preventative. She agreed to it.

"I was terrified that a second round would leave me permanently disabled and stuck in bed for the rest of my life," she said.

About 4 days after her monoclonal antibody treatment, she noticed that some of the brain fog that had persisted after COVID was lifting.

"By day 5, it felt almost like a heavy-weighted blanket had been lifted off of me," she recalled. "I was able to take my dog for a walk and go to the grocery store. It felt like I had gone from 0 to 100. As quickly as I went downhill, I quickly went back up."

Reasons for Recovery

Researchers have come up with a few theories about why monoclonal antibodies may help treat long COVID, said study coauthor Aileen Marty, MD, professor of translational medicine at the Herbert Wertheim College of Medicine at Florida International University. Among them:

  • It stimulates the body to fight off any residual virus. "We suspect that many of these patients simply have levels of virus that are so low they can't be picked up by conventional testing," said Marty. "The virus lingers in their body and causes long COVID symptoms. The monoclonal antibodies can zero in on them and knock them out." This may also help explain why some patients with long COVID reported a temporary improvement of symptoms after their COVID-19 vaccination.
  • It combats dysfunctional antibodies. Another theory is that people with long COVID have symptoms "not because of residual virus but because of junky antibodies," said Marty. These antibodies go into overdrive and attack your own cells, which is what causes long COVID symptoms. "This may be why monoclonal antibodies work because they displace the dysfunctional antibodies that are attached to a patient's cells," she explained.
  • Reactivation of other viruses. Long COVID is very similar to chronic fatigue syndrome, which is often thought to be triggered by reactivation of viruses like the Epstein-Barr virus, noted coauthor Nancy Klimas, MD, director of the Institute for Neuro-Immune Medicine at Nova Southeastern University in Fort Lauderdale. "It may not explain all of the cases of long COVID, but it could make up a subgroup," she said. It's thought that the monoclonal antibodies may perhaps neutralize this reactivation.

Where Research Is Headed

While Regeneron worked well in all three patients, it may be because they developed long COVID from either the initial virus or from early variants like Alpha, Beta, and Delta, said Pepe. As a result, it's unclear whether this treatment would work for patients who developed long COVID from newer strains like Omicron.

"What concerns me is I believe there may be many people walking around with mild long COVID from these strains who don't realize it," he said. "They may assume that if they have difficulty walking upstairs, or forget why they went into another room, that it's age related."

The next step, the researchers said, is to create a registry of volunteer patients with severe long COVID. Klimas plans to enroll 20 volunteers who were infected before September 2022 to see how they respond to another monoclonal antibody initially used to treat COVID-19, bebtelovimab. (Like Regeneron, bebtelovimab is no longer approved for use against COVID-19 by the US Food and Drug Administration because it is no longer effective against variants of the virus circulating today.)

As for patients who developed long COVID after September 2022, research is ongoing to see if they respond to other monoclonal antibodies that are in development. One such study is currently enrolling participants at the University of California San Francisco. The center is recruiting 30 patients with long COVID to try a monoclonal antibody developed by Aerium Therapeutics.

"They created an investigational monoclonal antibody to treat acute COVID, but it proved less effective against variants that emerged in late 2022," said lead investigator Michael Peluso, MD, an assistant professor of medicine in the Division of HIV, Infectious Diseases and Global Medicine at the University of California San Francisco. The hope is it may still work to fight long COVID among patients infected with those variants.

In the meantime, the three patients with long COVID who responded to Regeneron have resumed life as they knew it pre-COVID. Although two subsequently became infected with COVID again, they recovered quickly and did not see symptoms return, something which, for them, seems nothing short of miraculous.

"I had prepared myself to be disabled for life," one of the patients, a 46-year-old Floridian woman who developed long COVID after an infection in January 2021, told Medscape Medical News. "I had crippling fatigue and dizziness so intense I felt like I was walking on a trampoline. My brain fog was so pronounced I had to write everything down constantly. Otherwise, I'd forget."

When she became infected with COVID again in September 2021, "I thought I was going to die because I had no idea how I could possibly get worse," she recalled. Her doctors recommended Regeneron infusion treatment. Forty-eight hours later, her symptoms improved significantly.

"I was able to go out to a cocktail party and dinner for the first time in months," she said. "I would not have been able to do either of those things a week before."

It's also profoundly affected her husband, who had had to take over running the household and raising their five children, aged 11-22 years, for months.

"I can't tell you how many school events and sports games I missed because I physically didn't have the strength to get to them," she noted. "To this day, my husband gets upset whenever we talk about that time. Long COVID literally took over all of our lives. It was devastating to me, but it's just as devastating for loved ones, too. My family is just grateful to have me back."



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