Impact and effectiveness of Australia's 2025 hybrid RSV immunisation program: results from the PAEDS-FluCAN Network

Background Australia introduced a hybrid Respiratory Syncytial Virus (RSV) Maternal and Infant Protection Program (RSV-MIPP) in 2025, using National Immunisation Program-funded RSV vaccine for pregnant people from 28 weeks' gestation and jurisdiction-funded nirsevimab. We estimated real-world effectiveness and assessed the impact of the RSV-MIPP program across a participating surveillance network. Methods We conducted a national, prospective test-negative case–control study at thirteen PAEDS-FluCAN network hospitals contributing paediatric RSV data. From April 2024 to November 2025, hospitalised children with RSV-associated acute respiratory infection (ARI; cases) and contemporaneous RSV-negative controls were recruited. Immunisation effectiveness was estimated using a test-negative design with multivariable regression, adjusted for prespecified covariates, and calculated as (1−adjusted odds ratio) × 100% with 95% confidence intervals (CIs). Impact was assessed as the 2024–2025 change in the cumulative number of RSV hospitalisations during epidemiological weeks 14–48, excluding hospitals in two states with comprehensive 2024 nirsevimab programs, and stratified by age group. Findings Between 1 January and 30 November 2025, 3743 children were recruited (2719 RSV-positive cases; 1024 test-negative controls). Overall effectiveness against RSV-associated ARI hospitalisation in the RSV-MIPP newborn cohort (born from 17 February) was 82·6% (95% CI: 70·6, 89·7). Effectiveness estimates for maternal vaccination and nirsevimab were 81·5% (68·4, 89·2) and 89·6% (73·6, 95·9) respectively. Nirsevimab effectiveness in the catch-up cohort (born 1st October 2024–16th February 2025) was 89·6% (66·4, 96·8). The program's impact, based on a single preprogram comparison year and excluding 2 states, was associated with 43·8%, 20·1% and 8·5% reduction in hospitalisations in infants aged 0–<3 months, 3–<6 months and 6–12 months respectively. Interpretation These first southern hemisphere estimates of a hybrid RSV prevention program demonstrated high effectiveness against RSV hospitalisation over a single season. Longitudinal evaluation of the RSV-MIPP is needed to understand sustained effectiveness and year-round population level impacts. Funding This work was sponsored by the Australian Government Department of Health, Disability and Ageing and the Australian Centre for Disease Control.