Monoclonal Antibodies to Prevent SARS-CoV-2 Infection Shows Positive Results

Positive results of a phase 3 trial of Regeneron’s monoclonal antibodies treatment REGEN-COV among people at high risk for COVID-19 because of household exposure support the drug’s use for post-exposure prophylaxis.

Regeneron Pharmaceuticals’ combination of monoclonal antibodies casirivimab and imdevimab showed positive Phase 3 trial results for reducing the risk of SARS-CoV-2 infection among those at high risk for infection because of household exposure.

The randomized, double-blind, placebo-controlled clinical trial, published in the New England Journal of Medicine, included 1505 participants who had negative tests for SARS-CoV-2 and were seronegative at baseline, with 753 assigned to receive 1 dose of REGEN-COV (1200 mg) via subcutaneous injection and 752 who received a placebo. All participants were at high risk for SARS-CoV-2 infection because of household exposure to a person diagnosed with the virus within 96 hours, and 459 (30.5%) were at high risk for severe COVID-19 if they became infected with the virus.

Through Day 28, 11 participants in the REGEN-COV group (1.5%) developed symptomatic SARS-CoV-2 compared with 59 (7.8%) in the placebo group (relative risk reduction [1 minus the relative risk], 81.4%; P<0.001). The relative risk reduction for all infections, including asymptomatic cases, was 66.4%, with 36 (4.8%) overall infections among the REGEN-COV group and 107 (14.2%) in the placebo group.

REGEN-COV also was associated with a faster recovery from symptomatic infection, with resolution of symptoms 1.2 weeks among participants in the REGEN-COV group compared with 3.2 weeks among those in the placebo group. Duration of high viral load was shorter in the REGEN-COV group (0.4 weeks) than in the placebo group (1.3 weeks).

“Despite the increasing use of highly effective vaccines, SARS-CoV-2 has not been eradicated,” study author Meagan O’Brien, MD, of Regeneron Pharmaceuticals told Contagion. “Moreover, it is unclear how many people will ultimately choose to become vaccinated, how vaccine efficacy will wane over time, and how great a problem emerging variants of concern will be. For these reasons, a need will persist for complementary medicines such as REGEN-COV to prevent the spread of SARS-CoV-2 infection in persons who are not vaccinated, who have waning vaccine-mediated protection over time or because of the emergence of variants, or who are immunocompromised and cannot mount an antibody-mediated antiviral response.”

The study resulted in no adverse events of special interest, with 20.2% of those in the REGEN-COV group reporting adverse events compared with 29% in the placebo group. These included COVID-19, headache and injection-site reaction.

In January, the company announced that its therapy was effective in neutralizing SARS-CoV-2 variants B.1.1.7 and B.1.351, which emerged in the United Kingdom and South Africa respectively. It has also shown positive results against the Gamma (P.1, Brazilian) and Delta (B.1.1622 India) variants of SARS-CoV-2 and was associated with a 20% reduction in death among hospitalized COVID-19 patients who had not mounted their own immune response.

The Food and Drug Administration (FDA) recently expanded the Emergency Use Authorization for REGEN-COV to include post-exposure prophylaxis for those at high risk for severe COVID-19. EUA for treatment of mild to moderate COVID-19 was initially issued in November, marking the third investigational COVID-19 therapy to receive EUA after remdesivir and baricitinib.

Use of REGEN-COV has increased in the United States, surpassing weekly orders for 50,000 doses during the current COVID-19 surge, the company said in a statement. The drug, which is not a substitute for vaccination against COVID-19, will continue to be monitored for potency against emerging SARS-CoV-2 variants.