Background and aim

Respiratory syncytial virus (RSV) is the key respiratory pathogen of early childhood. Disease prevention is now possible through the use of vaccines and monoclonal antibodies. In April 2024, some Australian jurisdictions implemented prevention programs using a long-acting monoclonal antibody (nirsevimab) with varying eligibility criteria. We compared RSV incidence in infants across jurisdictions with and without nirsevimab programs.

Methods and analysis

Australian RSV notification data from 1 January–31 December 2024 were analysed. Jurisdictions were grouped by nirsevimab program type: comprehensive (WA, QLD), limited risk-based (NSW, ACT), and no/limited programs (Victoria, South Australia, Tasmania, Northern Territory). Crude incidence rates were calculated by age-group, and incidence rate ratios (IRRs) were calculated to compare program types by jurisdiction.

Outcomes

Before programs commenced in April 2024, baseline RSV activity was higher in jurisdictions with comprehensive or limited/risk-based programs compared with no/limited programs (January–March monthly IRRs 1.66–1.81 and 2.87–4.41, respectively). RSV incidence declined markedly in comprehensive program jurisdictions compared with no program jurisdictions, with monthly IRRs for children <24 months below 1 from May to July (0.55–0.73), particularly in infants <3 months (0.23–0.46). Jurisdictions with limited, risk-based programs showed more modest reductions (<24 months: IRRs 0.81–1.19, <3 months: 0.56–0.96).

From August onwards, RSV incidence increased across all jurisdictions. Some no/limited program jurisdictions experienced a delayed seasonal peak, resulting in higher relative incidence later in the year, while comprehensive program jurisdictions maintained a comparatively lower incidence. Reductions were most pronounced in the youngest infants and attenuated with increasing age.

Conclusion and future actions

Comprehensive nirsevimab programs were associated with substantial reductions in early-life RSV, particularly in younger infants. These results support emerging global evidence that early-life RSV prevention programs meaningfully reduce population-level burden. As Australia’s RSV prevention programs evolve, our findings support a continuing role for long-acting monoclonal antibodies.

Background/Aim:
The Queensland Paediatric Respiratory Virus Prevention Program (QPRSVP) commenced in April 2024 introducing Nirsevimab for eligible newborns and infants, before expanding to Abrysvo® for pregnant women. QPRSVP was expected to prevent serious illness caused by RSV and reduce related hospital admissions. However, a proportion of immunised infants and babies born to immunised mothers are still hospitalised with RSV-positive associated disease. This observational cohort study aimed to explore the impact of the program and characterise RSV infections resulting in hospitalisation.
Methods/Analysis:
Children <5yrs hospitalised with RSV-associated illness at a tertiary paediatric hospital in Queensland were prospectively recruited from April 2024, with an interim analysis at 9 months. Clinical, including immunisation status, viral and serological data were collected and a descriptive analysis performed. Additionally, age adjustment was performed to allow comparison between vaccinated and unvaccinated groups.
Outcomes:
To date 125 participants have been recruited with median age of 1.2 years (IQR 0.7–2.0), and 51.2% male. Almost three quarters (72%;n=90) met eligibility criteria for Nirsevimab or Abrysvo with less than half immunised (44%;n=55). However, eligible babies born after the program started had a higher immunisation rate of 79.3%. Overall median hospital admission was 2.88 days (IQR 1.93, 4.71). A logistic regression of under 2yr-olds showed no statistical difference in PICU admission and need for high flow/invasive ventilation between the two groups once adjusted for age. 84%(n=105) had a chest Xray performed with 90.5%(n=95) reported as abnormal (including non-specific perihilar changes). IV antibiotics were prescribed to 50.8% of patients with oral antibiotics and corticosteroids prescribed to 44.4% and 26.6% respectively.
Conclusion/Future Actions:
Recruitment will continue year-round for a further 2.5years. Serological surveillance will identify if breakthrough infections are due to waning immunity. RSV isolates have been stored and will undergo genomic sequencing to assess virulence and identify immunisation derived selection pressure.

Background and Aim
Respiratory syncytial virus (RSV) is a common cause of respiratory tract infections with the highest rates of diagnosed infection and hospitalisation in children less than two years old. Two immunisation products to protect against RSV in infants have recently become available in Australia: a long-acting monoclonal antibody, nirsevimab, for use in infants; and a vaccine, Abrysvo, for use in pregnant women. In NSW a targeted program provided nirsevimab for high-risk infants in 2024. In 2025, a whole of population year-round program was implemented providing Abrysvo, funded through the National Immunisation Program, and nirsevimab, funded by the NSW government. This study quantifies the population impact of the 2024 and 2025 programs.
Methods and Analysis
The relative rate (RR) of RSV outcomes, notification and hospitalisation, in infants aged 0-<6 months to those in infants aged 12-<18 months was calculated for each year. Comparison against the older age group was used to account for differences in amount of circulating RSV between years. The impact of the program was assessed by comparing the RR for 2025 to 2024 and 2023.
Outcomes
In 2025, 54,618 doses of Abrysvo were administered to women aged 14-45 years, and 8768 doses of nirsevimab were administered to infants aged less than 6 months. For diagnosed RSV infection the RR for 2025, 0.52 (95%CI 0.50-0.54) was significantly lower than for 2024, RR 0.71(95%CI 0.69-0.74), and 2023, RR 0.96 (95%CI 0.92-1.00). Similarly for RSV hospitalisations, the RR for 2025, 1.43 (95%CI 1.33-1.54) was significantly lower than for 2024, RR 2.01 (95%CI 1.88-2.15), and 2023, RR 2.53 (95%CI 2.36-2.72).
Conclusion
These results demonstrate a significant population level impact of the RSV prevention programs, with the impact of the 2025 program surpassing the 2024 program. This finding supports the continuation of the combined maternal and infant RSV prevention program.

Background and Aim: In February 2025, Australia introduced maternal RSVpreF vaccination in the National Immunisation Program for pregnant individuals ≥28 weeks’ gestation as the primary, year-round strategy to prevent respiratory syncytial virus (RSV) disease in infants aged ≤6 months.

Methods and Analysis: We conducted a retrospective case-control study with a test-negative design across six hospitals in Australia from March through October 2025. Infants aged ≤180 days hospitalised with acute respiratory illness (ARI) and tested for RSV were included—cases were RSV-positive and controls were RSV-negative. Infants were considered born to an RSVpreF-vaccinated mother if vaccination occurred ≥28 weeks’ gestation and ≥14 days before delivery. Multilevel logistic regression with confounder adjustment was used to calculate vaccine effectiveness (VE) as (1-adjusted odds ratio)*100%.

Outcomes: Of 435 infants hospitalised with ARI, 287 had lower respiratory tract disease (LRTD) with 36% of cases (LRTD: 60/165; ARI: 70/193) and 66-68% of controls (LRTD: 80/122; ARI: 165/242) born to RSVpreF-vaccinated mothers (mean gestational age at vaccination: 31 weeks). Median age among infants hospitalised with LRTD was 46 days (IQR 28-78) and 81% were ≤3 months. VE against RSV-LRTD hospitalisation among infants ≤3 months was 89.3% (95%CI: 80.4-94.2) and ≤6 months was 79.4% (67.3-87.0). VE against RSV-ARI hospitalisation was 82.9% (78.7-86.2) and 79.8% (75.4-83.4) ≤3 and ≤6 months, respectively. Among all infants hospitalised with ARI, 32% (63/200) born to mothers who did not receive RSVpreF progressed to severe LRTD, compared with 20% (46/235) among infants born to RSVpreF-vaccinated mothers.

Conclusion and Future actions: These real-world findings demonstrate high effectiveness of RSVpreF vaccination in pregnancy against RSV-LRTD and RSV-ARI hospitalisation in infants ≤6 months in the first year following introduction in Australia. Future analyses with larger sample sizes will evaluate effectiveness within key subgroups and stratifications important for informing vaccine policy, including by infant age groups.

Sponsorship: This was a Pfizer-sponsored study.

Background and Aim
Respiratory syncytial virus (RSV) is a leading cause of infant hospitalisation. In 2025, a national maternal RSV vaccination program (Abrysvo) was introduced, and infant monoclonal antibody protection (Nirsevimab) commenced in April in South Australia. This program evaluation aimed to estimate the effectiveness of maternal or infant RSV protection in preventing RSV hospitalisation among infants in South Australia.

Methods and Analysis
A test-negative case-control design was used for infants (born in 2025) admitted to metropolitan South Australian hospitals with acute respiratory tract infections. RSV PCR-positive admissions were classified as cases and RSV PCR-negative admissions as controls, matched 1:1 (+/- 2 weeks date of birth and +/- 1 month of admission date). Maternal RSV vaccination during pregnancy and infant receipt of Nirsevimab were identified from the Electronic Medical Record and the Australian Immunisation Register. RSV protection was defined as maternal vaccination > 2 weeks prior to birth, or infant Nirsevimab administered > 7 days prior to admission. Logistic regression, adjusted for age and month of admission, was used to estimate the odds ratio (OR), with effectiveness calculated as (1−OR)×100%.

Outcomes
A total of 178 admissions were included (89 RSV cases and 89 controls). RSV protection was provided in 37% of cases and 63% of controls. The adjusted OR for RSV hospitalisation among protected infants was 0.27 (95% CI, 0.14 to 0.54), corresponding to an estimated effectiveness of 73% (95% CI, 46% to 86%). None of the infants in the study whose mothers received Abrysvo also received Nirsevimab prior to the index admission. Demographic and perinatal characteristics were broadly similar between groups.

Conclusion and Future Actions
This South Australian program evaluation indicates that maternal RSV vaccination or infant nirsevimab is associated with substantially reduced odds of RSV hospitalisation.

Background: Respiratory Syncytial Virus (RSV) is a leading cause of morbidity in young children. Australia introduced a hybrid RSV Maternal and Infant Protection Program (RSV-MIPP) in 2025, including National Immunisation Program-funded RSV vaccine during pregnancy and jurisdiction-funded nirsevimab. We estimated real-world effectiveness and assessed the impact of the hybrid RSV-MIPP program across the PAEDS-FluCAN surveillance network.

Methods and Analysis: Thirteen hospitals collected paediatric RSV data between April 2024 and November 2025. Children hospitalised with laboratory-confirmed RSV-associated acute respiratory infection (ARI; cases) and contemporaneous RSV-negative controls were recruited. Immunisation effectiveness (IE) was estimated using a test negative design, incorporating multivariable regression models, adjusted for prespecified covariates and calculated as (1−adjusted odds ratio)×100%), with 95% confidence intervals (CIs). Impact was assessed as the reduction in the cumulative number of hospitalisations from epidemiological weeks 14 to 48 from 2024 to 2025, by age groups and excluding WA and QLD owing to nirsevimab programs in 2024.

Outcomes: Between 1st January and 31st November 2025, 1404 children recruited had known immunisation status (959 RSV-positive cases; 445 test-negative controls). Overall IE against RSV-associated ARI hospitalisation of the RSV-MIPP newborn cohort (born from 17th February) was 82.0% (95% CI: 70.0, 89.2). IE for maternal vaccination and nirsevimab was 80.8% (67.8, 88.6) and 89.5% (73.4, 95.8) respectively. Nirsevimab effectiveness for catch-up cohort (born 1st October 2024 to 16th February 2025) was 87.3% (63.8, 95.5). Among infants aged 0 to <3months, 3 to <6months and 6 to <12months, a 43.8%, 20.1% and 8.5% reduction in RSV hospitalisations from 2024 to 2025 was observed yet increased by 14.3% among children aged 1 to <5 years.

Conclusion: These first Australian observational estimates of the hybrid RSV prevention program demonstrated high effectiveness against RSV-associated hospitalisations over a single season. Longitudinal evaluation of the RSV-MIPP will be essential to understand sustained effectiveness and year-round programme impact.

Background and Aim
Victoria implemented a hybrid RSV Maternal and Infant Protection Program (RSV-MIPP) in 2025. Infants born April to September could be protected by maternal vaccine (Abrysvo) offered from 28 weeks gestation, or long-acting monoclonal antibodies (Nirsevimab) administered at or after birth. Infants born October 2024 to March 2025 were eligible for catch-up Nirsevimab.
Aim: To estimate effectiveness of maternal and infant immunisation against RSV-related endpoints in Victorian infants.
Methods and analysis
Maternal and infant immunisations and births were obtained from the whole-population linked data platform, Vaccine Safety Health Link, together with RSV related endpoints: laboratory-confirmed RSV infection; bronchiolitis emergency department (ED) presentations; RSV hospital and intensive care unit (ICU) admissions.
Infants were followed up from birth until 31 December 2025.
The incidence rate ratio (IRR) for each endpoint by immunisation status compared with unimmunised infants was calculated using Poisson regression. Effectiveness was estimated as 1-IRR.
Outcomes
68,757 liveborn infants were included in analysis. Coverage for infants born during RSV-MIPP was 67% (60% maternal, 7% infant immunisation), and 20% infant immunisation in the catch-up group.
For infants born in the RSV-MIPP period maternal and infant immunisation were both associated with reductions in incidence of laboratory confirmed RSV (63% [95% CI: 57%–69%] and 77% [64%–87%]), ED presentations (42% [35%–48%] and 32% [15%–46%]) and hospital admissions (72% [66%–78%] and 86% [73%–94%]). Maternal vaccination was effective against ICU admission (87% [70%–95%]). No ICU admissions occurred in infants who received nirsevimab.
Catch-up Nirsevimab was associated with a reduction in laboratory-confirmed RSV (66% [58%– 73%]), ED presentations (19% [9%– 29%]) and hospital admissions (86% [76%– 93%]).
Conclusion and future actions
Both maternal and infant immunisation demonstrated high effectiveness against RSV in the first year of life. Prospectively-linked population-level data can provide real-world effectiveness information rapidly during a new immunisation program.