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Nirsevimab effectiveness against hospitalised Respiratory Syncytial Virus infection in Portugal, 2024/25 season
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Background: Respiratory Syncytial Virus (RSV) is one of the leading causes of lower respiratory tract infections in younger children. In mainland Portugal, in order to reduce the risk of severe RSV post-infection complications, an immunisation strategy using Nirsevimab was implemented starting in October 2024, targeting all children aged less than 3 months, and those with high-risk conditions less than 24 months. We conducted a test-negative case-control study using the national hospital-based RSV surveillance network to estimate
Nirsevimab effectiveness (NE).
Methods: This multicentre study included children aged under 24 months hospitalised with severe acute respiratory infection in 14 hospitals. Cases were defined as children testing positive for RSV by RT-PCR or rapid antigen test (RAT), while controls tested negative. Immunisation status was obtained from electronic medical records. NE was estimated using logistic regression and estimated as (1 – adjusted odds ratio of immunisation) × 100, adjusting for age group, sex, month of symptom onset date, low birth weight,
prematurity, and chronic conditions.
Results: Between weeks 40/2024 and 12/2025, we included 111 cases and 110 controls. The median age for both groups was 2 months (IQR: 1–4). 44 (39.6%) RSV-positive and 80 (72.7%) RSV-negative infants received Nirsevimab at least 2 days before symptom onset. No significant differences were observed between cases and controls regarding sex or medical conditions. NE against RSV-associated hospitalisation was 85% (95% CI: 66–94) in the target population. Sensitivity analysis restricted to RT-PCR-confirmed cases yielded similar results.
Conclusions: During the first immunisation season in mainland Portugal, Nirsevimab conferred good protection against the most severe presentation of RSV infection in young children. Our results are aligned with those reported in other countries. Given the potential for viral evolution following the introduction of universal immunisation programmes, ongoing monitoring of NE is warranted.
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Palavras-chave
Nirsevimab VigiRSV Determinantes da Saúde e da Doença Observação em Saúde e Vigilância Estados de Saúde e de Doença Infecções Respiratórias
Contexto Educativo
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Sem licença CC