ROCHESTER, Minn. —A Mayo Clinic study has produced more evidence that early outpatient infusion of monoclonal antibodies (mAB) can dramatically reduce the risk of hospitalization for high-risk patients following diagnosis with COVID-19.

The study, published Monday, Aug. 30, in The Lancet journal EClinical Medicine, compared the outcomes for roughly 700 patients given the treatments with that of 700 control patients between December of 2020 and April of 2021.

This study used a combination of the biologics casirivimab and imdevimab, variant-tailored treatments manufactured by the drugmaker Regeneron.

The study evaluated patients two, three and four weeks after the outpatient treatments. It found that 3% to almost 5% of the group who did not get the medication ended up being hospitalized, but just over 1% of the treated group needed inpatient care.

As a result, the study reports, monoclonal antibodies lowered hospitalization by a relative risk reduction of 60-70%, with the rate of ICU admission and mortality low among those who were hospitalized.

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"This is exciting," says Mayo infectious disease specialist and study coauthor Dr. Raymund Razonable, "because we are providing the largest data on real-world practice on the use of monoclonal antibodies for the prevention of severe COVID-19 and hospitalization in patients with COVID-19."

"Early on when the FDA issued the EUA (emergency use authorization) there was not a lot of data to support the use," he added. "Based on what we see, the use of this monoclonal antibody product does prevent hospitalization, it does prevent ICU admission, and it does prevent death in patients with COVID-19."

The study is an improvement on the group's previous finding, a Journal of Clinical Investigation published earlier this year. It reported that the Eli Lilly-manufactured mAB known as bamlanivimab reduced hospitalizations in high-risk patients by 40%–60%.

Due to treatment resistance caused by virus mutation, the FDA in April revoked the EUA for bamlanivimab when given alone.

A nurse administers monoclonal antibody treatment. Photo: Mayo Clinic
A nurse administers monoclonal antibody treatment. Photo: Mayo Clinic

Monoclonal antibodies are lab-created versions of the antibodies created by the immune system.

Though the visibility of mAB treatments had taken something of a backseat in the public focus on vaccines, they are one of only a handful of interventions known to reduce severity of COVID-19.

They are recommended early in an infection for those with high risk of poor outcomes from COVID-19.

Recently the infusions have seen their profile elevated in Florida, where the governor has launched 17 free treatment sites in response to the state's explosion in cases.

They are available at select medical centers as experimental treatments, given on an outpatient basis in a single infusion early in a COVID-19 infection, with the goal of reducing the chance of hospitalization.

"It has to be a patient who is newly symptomatic, so it should be given early," Razonable said.

"If patients have symptoms they should get tested as soon as possible. If they belong to high-risk categories as detailed by the FDA — basically, high blood pressure, immunosuppression, kidney disease, heart disease, lung disease — any of them or they are older than 65, then they qualify to receive the mAB infusion."

"It's about 20 minutes to infuse, an hour for observation and that's it ... the drug is free but the infusion is covered by insurance. For those who don't have insurance, or who are underinsured, we give it to them with no charge."

Razonable says the treatments are used for breakthrough cases and the delta variant as well.