Passive immunization has a long history for infection prevention following exposure. We report results of a descriptive interim analysis from a study of an antibody ‘cocktail’ of casirivimab with imdevimab (cas/imdev; formerly REGN-COV2) designed to bind non-competing epitopes of the viral spike protein, as a potential passive vaccine for the prevention of COVID-19 in people at risk of infection from household contact.
In this ongoing Phase 3 study, asymptomatic participants exposed to a COVID-19–infected household member were randomized 1:1 to placebo or 1200 mg cas/imdev (600 mg of each antibody administered subcutaneously) within 96 hours of their household member testing positive. The analysis included participants who tested negative for SARS-CoV-2 by nasal, saliva, or nasopharyngeal swab and who were seronegative to SARS-CoV-2 antibodies at baseline. The proportion of participants who developed an RT-PCR-confirmed SARS-CoV-2 infection (asymptomatic or symptomatic) during the 1-month efficacy assessment period was summarized.
Initial results from the first evaluable 223 placebo and 186 cas/imdev participants who completed ?29 days of the study are reported. Reduction in PCR-positive symptomatic disease was 100% (0/186 cas/imdev vs 8/223 placebo; OR 0.00 [CI 0.00, 0.69]). Reduction in any PCR-positive infection (symptomatic or asymptomatic) was 48% (10/186 vs 23/223; OR 0.49 [CI 0.20, 1.12]). Placebo-group participants had on average 100-fold higher peak viral load. In the cas/imdev group, viral RNA was not detected for longer than 1 week but was detected for 3-4 weeks in approximately 40% of placebo participants (Fig. 1). The proportions of infected participants with high viral loads (>10^4 copies/mL) were 13/21 placebo vs 0/9 cas/imdev. Total weeks of viral RNA detection and high viral load were 44 and 22 weeks in the placebo group vs 9 and 0 in the cas/imdev group. Total symptomatic weeks were 21 for placebo vs 0 for cas/imdev. A similar proportion of participants experienced at least 1 serious adverse event: placebo, 3/222 and cas/imdev, 1/186; none were deemed related to study treatment. Injection site reactions were similar: placebo, 1.4%; cas/imdev, 2.6%.
In this descriptive interim analysis of participants at risk of SARS-CoV-2 infection from household transmission, a subcutaneous dose of the cas/imdev antibody cocktail prevented symptomatic infection, reduced overall infection, and decreased viral load and duration of viral RNA detection.