Related Experiment Video
Updated: Sep 10, 2025
An Improved and High Throughput Respiratory Syncytial Virus RSV Micro-neutralization Assay
Published on: January 26, 2019
Effectiveness of a targeted infant RSV immunization strategy (2024-2025): A multicenter matched case-control study in
Federica Attaianese1, Sandra Trapani2, Rino Agostiniani3
1Meyer Children's Hospital IRCCS, Pediatric Unit, Florence, Italy.
Insights
Nirsevimab effectively prevented respiratory syncytial virus (RSV) hospitalizations in infants under 12 months in a real-world setting. This long-acting antibody demonstrated high immunization effectiveness in a targeted seasonal program.
Area of Science:
- Pediatrics
- Immunology
- Infectious Diseases
Background:
- Nirsevimab, a long-acting monoclonal antibody, targets respiratory syncytial virus (RSV) to prevent infant hospitalizations.
- Clinical trial efficacy is established, but real-world data on targeted immunization strategies are limited.
Purpose of the Study:
- Evaluate nirsevimab effectiveness in preventing RSV-associated hospitalizations in infants under 12 months.
- Assess nirsevimab within a seasonal program prioritizing infants born from April onwards.
Main Methods:
- Prospective, multicenter, matched case-control study (N=138) in Italian hospitals during the 2024-2025 RSV season.
- Infants hospitalized with RSV bronchiolitis were matched 1:2 to controls hospitalized for non-respiratory causes.
- Immunization effectiveness (IE) estimated using conditional logistic regression and inverse probability of treatment weighting (IPTW).
Main Results:
- Adjusted IE was 89.5% (95% CI: 60.3-97.2%).
- Similar effectiveness observed in infants born after April 1 (IE: 88.4%) and those without risk factors (IE: 88.1%).
- IPTW analysis confirmed significant protection (IE: 79.6%).
Conclusions:
- Real-world evidence supports nirsevimab effectiveness in a targeted seasonal immunization program.
- Findings can inform RSV prophylaxis policies and phased implementation strategies.
- Nirsevimab offers a valuable tool for reducing infant RSV hospitalizations.
Background:
Nirsevimab, a long-acting monoclonal antibody against respiratory syncytial virus (RSV), was recently introduced to prevent infant RSV-related hospitalizations. Although efficacy has been demonstrated in clinical trials, real-world data on targeted immunization strategies remain limited. We aimed to evaluate the effectiveness of nirsevimab in preventing RSV-associated hospitalizations in infants under 12 months, within a seasonal program prioritizing infants born from April onwards.
Methods:
We conducted a prospective, multicenter, matched case-control study across seven Italian hospitals during the 2024-2025 RSV season. Infants hospitalized with PCR-confirmed RSV bronchiolitis were matched 1:2 by age and date of admission to controls hospitalized for non-respiratory causes. Data were collected via electronic medical records. Immunization effectiveness (IE) was estimated using conditional logistic regression adjusted for sex assigned at birth, gestational age, birth weight, and clinical risk factors. Two pre-specified stratified analyses and a sensitivity analysis using inverse probability of treatment weighting (IPTW) were performed.
Results:
A total of 138 infants were included (46 cases, 92 controls). Adjusted IE was 89.5% (95% CI: 60.3-97.2%). Stratified analyses yielded similar results among infants born after April 1 (IE: 88.4%, 95% CI: 56.5-96.9%) and those without risk factors (IE: 88.1%, 95% CI: 45.7-97.4%). IPTW analysis confirmed protection (IE: 79.6%, 95% CI: 53.5-91.0%).
Conclusions:
This study provides real-world evidence supporting the effectiveness of nirsevimab in a targeted seasonal immunization framework. These findings may inform phased implementation strategies and RSV prophylaxis policies in varied healthcare settings.
