Evidentia praxis: Nirsevimab and bronchiolitis prevention in term-born infants

We reviewed the published evidence on the efficacy and safety of nirsevimab, a monoclonal antibody, used to prevent respiratory syncytial virus (RSV) associated lower respiratory tract infections (LRTI) in term infants. We have found a randomized double-blind placebo-controlled clinical trial that included 3012 infants, born at term or late preterm, less than one year of age with a follow-up of at least 150 days. The quality of the evidence was classified as low for very severe LRTI and moderate for LRTI requiring medical care or admission. The evidence is based on a small number of events (only 29 cases for hospital admissions, 78 for IVRB with medical care), so any estimate must be considered imprecise. Efficacy, estimated as relative risk reduction (RRR) was 76.4% (95% confidence interval [95 CI]: 62.3 to 85.2) for RSV associated LRTI that required medical care and 76.8% (CI 95: 49.4 to 89.4%) for hospital admission. No differences were found in terms of safety. There are doubts about the clinical importance, due to the severity criteria used, and about its impact, with a number needed to treat of 63 to avoid a LRTI with hospital admission and of 24 to avoid LRTI requiring medical care. Based on the available information, it seems a safe intervention, from which we do not expect common adverse effects, but we cannot rule out low-frequency effects. We also expect to have more precise estimates of efficacy and safety soon.