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Current approved treatment protocols for COVID-19 involve provision of supportive care, such as supplemental oxygen or mechanical ventilation, and administration of remdesivir, an antiviral drug. Results of a recent phase 3 clinical trial demonstrate that REGEN-COV, a combination of the monoclonal antibodies casirivimab and imdevimab, improves outcomes in people who have COVID-19.

Monoclonal antibodies are proteins that mimic the body’s natural antibodies. They are mass-produced in a laboratory setting and help the body combat harmful pathogens such as viruses. In late 2020, the Food and Drug Administration granted emergency use authorization for REGEN-COV as a post-exposure treatment for patients meeting specific criteria based on robust data from phase 1 and phase 2 clinical trials. REGEN-COV has demonstrated activity against current variants of concern and those of interest, including the alpha, beta, delta, epsilon, gamma, and iota variants.

The phase 3 trial involved three cohorts of non-hospitalized participants who had tested positive for COVID-19 less than 72 hours prior to entering the trial. Cohort 1 included participants who were 18 years of age or older (average age, 50 years); cohort 2 included participants who were younger than 18 years of age; and cohort 3 included participants who were pregnant. Investigators randomly assigned participants in cohort 1 to receive REGEN-COV at a dose of either 1,200 milligrams (600 milligrams of each antibody), 2,400 milligrams (1200 milligrams of each antibody), or a placebo, delivered via intravenous infusion. The investigators measured antibodies against SARS-CoV-2 in the participants' blood and categorized the participants as antibody-positive, antibody-negative, or other, if the test was inconclusive. They also measured the participants' viral load. Participants tracked their symptoms and reported them using a validated electronic diary.

Because the trial for cohorts 2 and 3 is ongoing, this report included data for cohort 1 only. The trial demonstrated that 1.3 percent of participants who received the 2,400-milligram dose and 4.6 percent of participants who received a placebo required hospitalization or died; similarly, 1.0 percent of participants who received the 1,200-milligram dose and 3.4 percent of those who received a placebo required hospitalization or died. Participants with a high viral load were more likely to be hospitalized or die than participants with a low viral load. Symptom resolution among participants who received the monoclonal antibody treatment occurred four days earlier than those who received a placebo; similarly, viral load reduction was faster with monoclonal antibody treatment than with the placebo. Serious adverse events were rare and occurred more often among participants who received the placebo.

These findings suggest that the combined monoclonal antibody treatment REGEN-COV demonstrates efficacy against COVID-19 and exhibits a strong safety profile. Learn more about COVID-19 treatments in this episode featuring Dr. Roger Seheult.

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