Background: Respiratory syncytial virus (RSV) is a major cause of hospitalization in infancy, particularly during the first months of life. Nirsevimab has substantially reduced RSV-related hospitalizations in early real-world studies, but the incremental population-level benefit of expanding an established seasonal programme to broader birth cohorts remains uncertain. In Emilia-Romagna, Italy, nirsevimab was introduced for the 2024-25 RSV season as seasonal at birth immunoprophylaxis and expanded in 2025-26 to include at-birth immunoprophylaxis for infants born from August 2025 through March 2026 and catch-up immunization for infants born from April through July 2025. We assessed whether this expanded strategy provided an additional reduction in RSV compatible hospitalizations. Methods: We conducted a multicentre, population-based observational before-after study using hospital discharge records from eleven centres, covering approximately 69% of hospitalizations among infants aged <12 months. RSV compatible hospitalizations were compared across three seasons: Pre-Nirsevimab (2023-24), Seasonal (2024-25), and Extended seasonal + catch-up (2025-26). Incidence rate ratios (IRRs) were estimated by negative binomial regression adjusted for sex and age. Net avoided hospitalizations were also calculated. Results: Age-standardized RSV-compatible hospitalization rates declined from 21.9 per 100, 000 person-days in 2023–24 to 10.1 in 2024–25 and 7.8 in 2025-26. Compared with the Seasonal strategy, the Extended seasonal + catch-up strategy was associated with a further 22% reduction in hospitalization risk (IRR0.78; 95% CI 0.69–0.88; p<0.001) and a 64% reduction versus Pre-Nirsevimab (IRR 0.36; 95% CI 0.31–0.42). An estimated 103.3 additional hospitalizations were avoided versus 2024–25 and 677.8 versus Pre-Nirsevimab, corresponding to approximately 52 and 339 avoided hospitalizations per 10,000 infants, respectively. Findings were consistent in infants aged 0-180 days. Conclusions: Expanding nirsevimab immunoprophylaxis was associated with a further significant reduction in RSV-compatible hospitalizations beyond thatachieved with seasonal-only administration. Given the observational design,causal inference should remain cautious.
Impact of expanding nirsevimab immunoprophylaxis, extended window and catch-up, on RSV hospitalizations in infants: a three-season, multicentre, population-based study in Emilia-Romagna, Italy / Esposito, S.M.R., Bendoni, S., Maglietta, G., De Fanti, A., Ghizzi, C., Biasucci, G., Marchetti, F., Olivia Loredana Rosa Aricò, M., Vergine, G., Stella, M., Lanari, M., Guidi, B., Suppiej, A., Alberghi, F., Filice, E., Cannalire, G., Accomando, F., Miniaci, A., Miceli, A., Malaventura, C., et al.. - In: FRONTIERS IN IMMUNOLOGY. - ISSN 1664-3224. - (2026). [10.3389/fimmu.2026.1974003]
Impact of expanding nirsevimab immunoprophylaxis, extended window and catch-up, on RSV hospitalizations in infants: a three-season, multicentre, population-based study in Emilia-Romagna, Italy
Susanna Maria Roberta Esposito
;Giuseppe Maglietta;Chiara Ghizzi;Giacomo Biasucci;Gaia Giorgia Arnesano;Valentina Fainardi;Matteo Puntoni;Caterina Caminiti
2026-01-01
Abstract
Background: Respiratory syncytial virus (RSV) is a major cause of hospitalization in infancy, particularly during the first months of life. Nirsevimab has substantially reduced RSV-related hospitalizations in early real-world studies, but the incremental population-level benefit of expanding an established seasonal programme to broader birth cohorts remains uncertain. In Emilia-Romagna, Italy, nirsevimab was introduced for the 2024-25 RSV season as seasonal at birth immunoprophylaxis and expanded in 2025-26 to include at-birth immunoprophylaxis for infants born from August 2025 through March 2026 and catch-up immunization for infants born from April through July 2025. We assessed whether this expanded strategy provided an additional reduction in RSV compatible hospitalizations. Methods: We conducted a multicentre, population-based observational before-after study using hospital discharge records from eleven centres, covering approximately 69% of hospitalizations among infants aged <12 months. RSV compatible hospitalizations were compared across three seasons: Pre-Nirsevimab (2023-24), Seasonal (2024-25), and Extended seasonal + catch-up (2025-26). Incidence rate ratios (IRRs) were estimated by negative binomial regression adjusted for sex and age. Net avoided hospitalizations were also calculated. Results: Age-standardized RSV-compatible hospitalization rates declined from 21.9 per 100, 000 person-days in 2023–24 to 10.1 in 2024–25 and 7.8 in 2025-26. Compared with the Seasonal strategy, the Extended seasonal + catch-up strategy was associated with a further 22% reduction in hospitalization risk (IRR0.78; 95% CI 0.69–0.88; p<0.001) and a 64% reduction versus Pre-Nirsevimab (IRR 0.36; 95% CI 0.31–0.42). An estimated 103.3 additional hospitalizations were avoided versus 2024–25 and 677.8 versus Pre-Nirsevimab, corresponding to approximately 52 and 339 avoided hospitalizations per 10,000 infants, respectively. Findings were consistent in infants aged 0-180 days. Conclusions: Expanding nirsevimab immunoprophylaxis was associated with a further significant reduction in RSV-compatible hospitalizations beyond thatachieved with seasonal-only administration. Given the observational design,causal inference should remain cautious.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
