Phase I open-label study of the respiratory syncytial virus monoclonal antibody clesrovimab: Safety and tolerability in healthy Chinese participants.

In China, respiratory syncytial virus (RSV) is the primary cause of acute lower respiratory tract infections (LRTIs), particularly in infants and young children. Clesrovimab is a half-life‒extended RSV neutralizing monoclonal antibody for the prevention of RSV-associated LRTIs in infants. This Phase I, open-label, single-dose study, evaluated the safety and tolerability of clesrovimab in Chinese participants (EudraCT 2021-000432-58). Healthy male adults, children, and infants were sequentially enrolled in one of 3 panels, each with 25 participants. All participants received a single dose of clesrovimab (105 mg dose at 100 mg/mL concentration) on Day 1 in the deltoid or thigh muscle, beginning with male adults, followed by children, then infants, and were followed up through Day 365 postdose. Clesrovimab was generally well tolerated in healthy Chinese participants. Overall, 36.0% of male adults, 76.0% of children, and 56.0% of infants experienced at least one adverse event (AE), most were considered mild to moderate. Between Days 1 and 5 postdose, 12.0% of participants reported solicited injection site AEs (all drug-related), and 12% of infants reported solicited systemic AEs. One participant in panel A reported an anaphylaxis/hypersensitivity AE of special interest (AESI) on Day 24 postdose, not considered drug-related. No rash AESI from Day 1 through Day 42 postdose, and no serious AEs, deaths, study discontinuations or drug-related pauses were reported. These findings support the inclusion of a Chinese cohort in the global Phase IIb/III trial (NCT04767373) to evaluate the efficacy and safety of clesrovimab in healthy preterm and full-term infants.