TOPLINE

Pediatric hospitalizations for respiratory syncytial virus (RSV) declined by more than 40% across Italy during the 2024-2025 season following regional nirsevimab immunization programs. Regions with broader eligibility criteria and earlier program initiation saw greater reductions, while those with narrower criteria or delayed rollout experienced modest declines or no clear change.

METHODOLOGY

• Researchers characterized RSV hospitalization trends over 6 seasons to assess changes after the introduction of regional nirsevimab strategies in Italy, using a retrospective analysis of RSV-related hospitalizations in patients younger than 18 years across 19 Italian pediatric units.
• A total of 10,915 RSV-related hospitalizations were recorded from January 2019 through March 2025.
• Participating centers were grouped (Groups A through G) based on RSV prevention policy adopted by their region during the 2024-2025 season and timing of campaign initiation. All included centers experienced the 2024-2025 season as the first season with nirsevimab implementation.
• A negative-binomial model was used to estimate group-level ratios comparing the total number of hospitalizations during the 2024-2025 epidemic season with the pre-immunization baseline rates.

TAKEAWAY

• After the introduction of nirsevimab immunization, the 2024-2025 RSV season saw a 43.6% overall reduction in RSV-related hospitalizations among children younger than 18 years.
• Groups with broader eligibility and earlier initiation showed the largest reductions, with hospitalization count ratios of 0.28 (95% CI, 0.22-0.36) and 0.40 (95% CI, 0.22-0.74), corresponding to reductions of more than 70% in Group B and 60% in Group A, respectively.
• Groups C, D, and E, which applied more stringent strategies, exhibited more modest reductions with ratios ranging from 0.58 to 0.70, and Group C spanned unity (0.58; 95% CI, 0.27-1.25).
• Group G, where nirsevimab was introduced late during the 2024-2025 RSV season, showed no clear reduction after accounting for baseline variability.

IN PRACTICE

"[The] present study supports a broader reflection: effective immunization likely depends not only on scientific efficacy but also on strategic, timely, and equitable implementation. As nirsevimab is progressively integrated into routine infant care, continued surveillance, harmonized coverage monitoring, and age-specific analyses will be essential to fully assess its impact and inform future prevention policies across diverse settings," the authors wrote.

SOURCE

The study was led by Federica Attaianese, Meyer Children's University Hospital IRCCS in Florence, Italy. It was published online on August 26 in International Journal of Infectious Diseases.

LIMITATIONS

The observational design cannot establish causation. The case identification for RSV relied on administrative codes, which may have varied across centers. As the outcome included all children under 18, any decline among older children for any reason would appear as an overall reduction, so the decrease cannot be attributed specifically to the immunized group.

DISCLOSURES

The study was supported by the Current Research Annual Funding of the Italian Ministry of Health. Two authors reported receiving grants and personal fees from various sources.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.