Real-world effectiveness of nirsevimab against respiratory syncytial virus disease in infants: a systematic review and meta-analysis.

BACKGROUND: Nirsevimab was approved in 2023, and implemented in all-infant immunisation programmes in several high-income countries to prevent lower respiratory tract infection (LRTI) caused by respiratory syncytial virus (RSV). Knowledge of real-world effectiveness of broad nirsevimab programmes is crucial to validate the benefits observed in clinical trials and guide immunisation policy. We assessed the real-world effectiveness of nirsevimab in populations where infant immunisation programmes were introduced.

METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, Web of Science, Scopus, Global Health, and medRxiv from Jan 1, 2023, to Feb 25, 2025, to identify observational studies of immunisation programmes for infants aged 2 years or younger in routine clinical practice reporting original data for the real-world effectiveness of nirsevimab. The primary analysis focused on infants aged 12 months or younger. Pooled analyses were done with inverse-variance random-effects models for RSV-related hospital admissions, intensive care unit (ICU) admissions, and RSV-related LRTI incidence. For length of hospital stay, we used a restricted maximum likelihood random-effects model to estimate the weighted mean difference (WMD) in days between the nirsevimab and control groups. This study is registered with PROSPERO (CRD42024628782).

FINDINGS: We identified and screened 1238 records, of which 32 cohort and case-control studies from five countries (France, Italy, Luxembourg, Spain, and the USA) were included in the systematic review and 27 of them were included in the meta-analysis. Nirsevimab was associated with a lower odds of RSV-related hospitalisation (odds ratio 0·17; 95% CI 0·12-0·23; I2=85·8%), a lower odds of ICU admission (0·19; 0·12-0·29; 55·6%), and a lower odds of LRTI incidence (0·25; 0·19-0·33; 35·1%) in infants aged 0-12 months. However, length of hospital stay did not differ between the nirsevimab and control groups (WMD 0·01; 95% CI -0·63 to 0·65; I2=62·3%).

INTERPRETATION: Our findings indicate that the benefits of nirsevimab observed in clinical trials are also evident in real-world settings, effectively reducing the burden of RSV disease in infants and, consequently, health-care use.

FUNDING: Natural Sciences and Engineering Research Council of Canada and the Canadian Immunization Research Network.