Meagan P. O'Brien, M.D., from Regeneron Pharmaceuticals in Tarrytown, New York, and colleagues randomly assigned participants aged 12 years and older enrolled within 96 hours after a household contact received a diagnosis of SARS-CoV-2 infection to receive 1,200 mg REGEN-COV or matching placebo by subcutaneous injection.

The researchers found that symptomatic SARS-CoV-2 infection developed in 1.5 percent of the 753 participants in the REGEN-COV group and in 7.8 percent of 752 participants in the placebo group (relative risk reduction, 81.4 percent). In weeks 2 to 4, 0.3 and 3.6 percent of participants in the REGEN-COV and placebo groups, respectively, had symptomatic SARS-CoV-2 infection (relative risk reduction, 92.6 percent). Symptomatic and asymptomatic infections were prevented by REGEN-COV (relative risk reduction, 66.4 percent). With REGEN-COV versus placebo, among symptomatic infected participants, median time to resolution of symptoms was shorter (1.2 versus 3.2 weeks), as was the duration of a high viral load (0.4 versus 1.3 weeks).

"A need will persist for a complementary approach 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 authors write. "REGEN-COV has potential use as long-term prophylaxis in persons at risk for SARS-CoV-2 infection."

The study was partially funded by Regeneron Pharmaceuticals and F. Hoffmann-La Roche.

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