Abstract / Summary
Abstract Respiratory syncytial virus (RSV) is a major cause of acute respiratory tract infections in young children worldwide. Acute otitis media (AOM) is among the most frequent complications of RSV infection and the leading indication for antibiotic prescribing in this age group. The aim of this study was to evaluate the effectiveness of nirsevimab in reducing the incidence of AOM among infants. We conducted a nationwide register-based interrupted time-series study using data on live births, laboratory-confirmed RSV detections, and AOM diagnoses from four consecutive RSV seasons (2022–2023 to 2025–2026). Monthly infant populations at risk were reconstructed from birth cohorts to estimate incidence rates during the peak RSV seasons (December–March) which were compared between two pre-implementation and two post-implementation RSV seasons in infants aged < 12 months, stratified into age groups of 0–2, 3–5, and 6–11 months. The study population consisted of 181,999 infants and the follow-up consisted of 2,022,261 infant-months. A total of 3699 RSV-positive findings and 15,830 AOM diagnoses were included in the primary analysis. Following nirsevimab implementation, the incidence of AOM and RSV among infants aged < 12 months decreased by 44% (RR 0.56, 95% CI 0.54–0.58) and 83% (RR 0.17, 95% CI 0.15–0.18), respectively. The reduction was greatest in the youngest age (0–2 months) group. Conclusion : Implementation of a nirsevimab immunisation programme was associated with a substantial reduction in AOM incidence among infants aged < 12 months, suggesting that RSV immunisation may reduce the burden of AOM in early childhood. What's Known :• RSV is a major cause of morbidity during infancy, and acute otitis media is among its most frequent complications. • Nirsevimab has demonstrated high efficacy in preventing severe RSV disease in young children; however, its effect on outpatient RSV-related complications has not been well established. What is New: • This study provides population-based real-world evidence on the impact of nirsevimab on acute otitis media. • Following the implementation of nirsevimab prophylaxis, the incidence of acute otitis media among infants decreased significantly.