The Effectiveness of Nirsevimab on Antibiotic Use in Children Using Target Trial Emulation.

BACKGROUND: Nirsevimab is a monoclonal antibody with demonstrated efficacy in preventing respiratory syncytial virus (RSV) infections in infants. Because acute respiratory tract infections (ARTIs), including viral infections, often lead to antibiotic prescribing, we aimed to determine the effectiveness of nirsevimab on antibiotic prescribing among infants with medically attended ARTIs. METHODS: A primary care attendee cohort was established using electronic health record data from 32 diverse practices across a healthcare network to emulate a target trial comparing nirsevimab to no treatment among infants <8 months. Eligible infants were seen at a primary care practice within 14 days of life. Primary outcomes included time to first antibiotic prescription for (1) outpatient ARTIs, (2) outpatient encounters for bronchiolitis, and (3) RSV-related hospitalizations. Nirsevimab effectiveness was calculated as 1 minus the risk ratio for each primary outcome. RESULTS: Among 15 341 patients who met inclusion criteria, 7413 received nirsevimab. Compared with no treatment, nirsevimab administration led to a 14.4% (95% CI: 7.8%, 20.6%) reduction in antibiotic prescribing for outpatient ARTIs, a 40.3% (95% CI: 25.1%, 52.5%) reduction in antibiotic prescribing for outpatient bronchiolitis, and a 69.4% (95% CI: 4.8%, 90.1%) reduction in antibiotic prescribing for RSV-related hospitalizations. CONCLUSIONS: Nirsevimab administration in primary care reduced antibiotic use for ARTIs in both ambulatory and inpatient settings.