A meta-analysis (N= 45,238 patients) published in 2024 analyzed five randomized controlled trials (RCTs), seven real-world reports, and one official report from health authorities to determine the efficacy of nirsevimab in the prevention of lower respiratory tract diseases (LRTD) secondary to respiratory syncytial virus (RSV) in children and newborns. Studies included patients aged <2 years who had at least one dose of nirsevimab for RSV prevention. Pooled data assessing the incidence of hospital admission due to RSV led to an immunization efficacy of 88.40% (95% confidence interval [CI] 84.70% to 91.21%). However, immunization efficacy waned and the risk of breakthrough infections increased as observation time continued. A higher risk of breakthrough infections in studies with observation times ≥150 days versus <150 days was seen (risk ratio [RR] 2.170; 95% CI 1.860 to 2.532), with findings contradicted by a meta-regression analysis on the effect of observation time on immunization efficacy. While authors concluded the delivery of nirsevimab to be effective in preventing hospital admissions due to LRTD, one should take into consideration the degree of heterogeneity in data collection, the impact of the COVID-19 pandemic on study protocols, and the potential emergence of nirsevimab resistance. [1]