Background and aim
Despite widespread vaccination, SARS-CoV-2 transmission persists. Booster policies emphasise durability and breadth of protection. Data comparing immune responses and infection risk following fourth-dose boosters across vaccine platforms are limited. We compare SARS-CoV-2 infection incidence and timing, describe detected variants, and characterise pre- and post-infection humoral/cellular immune responses among adults with and without a fourth COVID-19 vaccine dose.

Methods and analysis
From 28 February to 4 October 2023, adults in Melbourne were randomised 1:1 to Moderna (Ancestral) or Novavax (Ancestral and Omicron BA.1 or BA.4/5) fourth-dose COVID-19 vaccine, stratified by age (18–49 and >50 years), with self-selected controls (no fourth-dose). Participants were followed for 12 months. SARS-CoV-2 infection was identified through symptom-triggered rapid antigen testing; nasopharyngeal swabs were collected for variant sequencing and blood samples taken 28 days post-infection. Humoral (binding IgG and surrogate neutralisation [sVNT]) and cellular (IFNγ) immune responses to Ancestral and Omicron variants were measured. Infection incidence, time to first infection, and immune responses were compared across study arms and between participants with and without early (0-6 months) or late (7-12 months) infection.

Outcomes
Among Moderna (n=177), Novavax (n=176) and control (n=143), SARS-CoV-2 infection occurred in 58 (33%), 52 (30%), and 47 (33%) participants, respectively. Time to first infection was longer among vaccinees (Moderna: median 230 days [IQR 163-291]; Novavax: 208 [90-255]; controls: 191 [125-264]). Most were Omicron lineages, reflecting contemporaneous circulation. Pre-infection IgG/sVNT levels were highest among Moderna recipients, followed by Novavax and controls, while IFNγ levels were similar across arms. Post-infection IgG/sVNT levels were highest among Moderna recipients with early infection, while IgG/sVNT/IFNγ levels were similar across other arms and follow-up periods.

Conclusion and future actions
SARS-CoV-2 infection incidence and variants were similar regardless of fourth-dose vaccination status. A fourth-dose provides some protection against infection for the first six months, but the immune responses post-infection are similar regardless of fourth-dose receipt.

Background and Aim: The nasal spray Live Attenuated Influenza Vaccine (LAIV) and injectable inactivated influenza vaccine (IIV) are considered comparably effective against influenza in children. Data from Finland suggests paediatric vaccine coverage rates (VCR) may be higher when both LAIV and IIV are available, and when LAIV is available via publicly funded immunisation programmes. The PEARL study aimed to explore the association between country-level availability of LAIV and overall uptake of any influenza vaccine in children and adolescents.
Methods and Analysis: We performed a cross-sectional, ecological analysis using publicly available, country-level data from international organisations. The analysis included Northern Hemisphere countries with paediatric influenza vaccination recommendations for season 2024/25. LAIV availability was categorised as a binary variable, controlling for healthcare typology (Public – Full, Public – Partial, and Private). VCR was defined as proportion of children and adolescents <18 years of age who received either LAIV or IIV during 2024/25 season. β-regression assessed association between LAIV availability and VCR, considering 27 covariates (demographic, socio-economic, health, behavioural and influenza-related) for adjustment via two approaches: Model 1 used LASSO selection, Model 2 used literature-informed covariate selection.
Outcome: Thirty-six countries were analysed: 20 (55.6%) offered only IIV and 16 (44.4%) offered both LAIV and IIV (1 private, 15 public). Median paediatric VCR was 11.1%, ranging from 0.1% (Azerbaijan) to 63.7% (Republic of Korea). VCR was notably higher in countries with publicly funded LAIV programmes compared to those offering only IIV. The odds ratios for LAIV availability (Public vs None) were 2.66 (95% CI: 1.37 - 5.15) in Model 1 and 1.87 (95% CI: 0.66 - 5.29) in Model 2.
Conclusions: Publicly funded programmes offering LAIV in addition to IIV are associated with higher paediatric influenza vaccine coverage. Further research should assess clinical and public health implications of higher VCR from expanded LAIV access.

Background and Aim

This presentation outlines how Australia’s national human respiratory surveillance system supports early risk assessment for highly pathogenic avian influenza (HPAI), and the role of One Health integration in interpreting surveillance signals under conditions of low prevalence.

The global epidemiology of HPAI continues to evolve, with increasing geographic spread and viral diversity impacting human and animal populations and their shared natural ecosystems. While Australia has not experienced avian influenza in human (AIH) transmission, global circulation of HPAI (particularly H5 viruses), combined with migratory bird pathways, regional connectivity and exposure to global travel and trade place it within a broader Indo‑Pacific risk environment that requires sustained vigilance. The Australian Centre for Disease Control (CDC) plays a central role in strengthening preparedness through independent, evidence-informed public health guidance and coordination across jurisdictions and sectors.

Methods and Analysis

Australia’s national respiratory disease surveillance system provides near real‑time situational awareness of influenza‑like illness and laboratory‑confirmed influenza activity. However, HPAI is not routinely captured within human respiratory surveillance, and routine influenza surveillance alone is unlikely to detect AIH in early phases without additional prioritisation. High testing volumes, limited routine influenza A subtyping, and reliance on clinician‑identified epidemiological risk represent key gaps that constrain early detection. Despite these limitations, respiratory surveillance provides critical baseline intelligence for escalation. Interpreted alongside integrated surveillance from state and territory partners, WHO Collaborating Centres, and national and reference laboratories, enables targeted subtyping, confirmatory testing, and timely follow‑up of exposed individuals in line with the national avian influenza surveillance objectives.

Conclusion and Future Actions

The establishment of the national HPAI Taskforce strengthens this approach by embedding a One Health, whole‑systems preparedness model. Improved cross‑sector communication, strengthened data‑sharing arrangements, and integrated surveillance planning enable human respiratory surveillance signals to be interpreted alongside animal and environmental intelligence, supporting earlier evidence‑informed public health decision‑making and identifying priorities for future integrated surveillance models.

Background and Aim: School-aged children play an important role in community transmission of influenza. We assessed the relationship between public-school holidays and influenza notifications by age group in Queensland to quantify risk and support management of influenza.

Methods and Analysis: Influenza notifications in Queensland from 1 January to 31 December 2025 were analysed by age groups (<5, 5–11, 12–17, 18–64, 65–74, ≥75 years). Notification rates and relative risks during public-school holidays were compared with the periods before and after the holidays using negative binomial regression.

Outcomes: Influenza notification rates were highest among children aged <5 years (3,451 per 100,000) followed by 5–11 years (3,283 per 100,000) and 12–17 years (2,128 per 100,000). During the winter school holidays (weeks 26–28), notification rates declined by 34% and 49% among children aged 5–11 and 12–17 years, respectively, while increasing among other age groups (53% increase among parental age group (35–49 years)). In the post-holiday period (weeks 29–31), notification rates increased by 77% and 63% among the two school-aged cohorts, respectively. During holidays, incidence rate ratios were lower among children aged 5–11 years (0.68; 95% CI 0.63–0.73) and 12–17 years (0.60; 95% CI 0.54–0.65) compared with adults aged 18–64 years (P<0.05). Reductions were observed across all age groups during autumn (weeks 14–17) and spring (weeks 38–41) holidays, with the largest reductions among school-aged children.

Conclusion and Future actions: School holiday periods were associated with a reduced transmission risk among school-aged children. Laboratory testing data would supplement these findings. These results provide insights to guide timing for promotion of influenza vaccination among children and messaging to reinforce exclusion of infectious cases before school reopening, when influenza activity often peaks. Extension of holidays or temporary closure may be considered as an intervention during community outbreaks.

Background and Aims

In 2025 Australia recorded its largest influenza season since 2001 based on NNDSS laboratory-confirmed cases. The season was dominated by influenza A(H1N1)pdm09 viruses with some influenza B circulation until a new A(H3N2) variant (subclade K) emerged later in the season. These viruses were first detected in the US in June/July 2025 along with their first detections in Australia. From August, influenza A(H3N2) cases grew rapidly with subclade K viruses causing a second yearly peak and a prolonged 33-week season. Although K viruses rapidly spread, they did not appear more severe than previously circulating A(H3N2) viruses, as infection-related hospitalisations and deaths were not exceptional. Phylogeographic mapping showed that from Australia, the K viruses spread to several countries including New Zealand, Singapore, Fiji, New Caledonia and the Philippines.

As the K viruses were antigenically and genetically distinct from previously circulating A(H3N2) viruses (including the A(H3N2) component of the Australian 2025 influenza vaccine), it was important to determine the vaccine effectiveness (VE) of the 2025 vaccine against the K viruses.

Methods and Analysis

Using a test-negative case-control design, we estimated VE against medical attendance through the ASPREN general practitioners’ network and VE against hospitalisation through the FluCAN/PAEDS network.

Outcomes

VE estimates were similar to previous seasons and other subtypes. VE for preventing medical attendance for A(H3N2) K viruses for all ages was 48% (95% CI; 6-71), for children (<18 years) 72% (95% CI; 10-91), and for adults (18-64 years) 43% (95% CI; -41-77); estimates for elderly (65+ years) had insufficient data. VE for preventing hospitalisation for A(H3N2) K viruses for all ages was 31% (95% CI; 7-50), for children 41% (95% CI; 8-62), and for elderly 55% (95% CI; 17-76); estimates for adults had insufficient data.

Conclusion and Future actions

These data highlight the value in being vaccinated against influenza even in the face of a newly emerging, distinct virus.

Background and Aim

Although RSV infection is recognised as a major cause of hospitalisation and death in adults, there is limited data on the burden of disease in Australia. This study aimed to estimate the incidence of hospitalisation, length of stay, in-hospital mortality and cost of RSV in Queensland in adults.

Methods and Analysis

We linked polymerase chain reaction (PCR) positive RSV notifications in adults ≥18 years between 1 March 2024 and 28 February 2025 to hospitalisation in all Queensland public and private hospitals within -14 to +3 days using a comprehensive database including ICD-10 codes, clinical and death data. A separate cohort of patients with data available was used for cost analysis.

Outcomes

From 18,110 cases of RSV, there were 1705 hospital admissions (9.4%, 95% CI 9.0 to 9.8%), age standardised rate 42.6 (95% CI 40.6 to 44.6) per 100,000 people. RSV‑hospitalised adults frequently had comorbidities, most commonly chronic respiratory disease (50.9%), diabetes (23.8%), and heart disease (13.4%). Hospitalisation incidence closely correlated to age with 223.6 (95% CI 208.6 to 239.3) admissions per 100,000 people aged ≥75 years. The median (IQR) length of stay was 3 (2-6) days. There were 85 deaths in hospital (5.0%, 95% CI 4.0 to 6.1%). Major independent risk factors for death were age ≥75 years and baseline cardiac disease, immunocompromise and chronic kidney disease. For patients with cost data available, the total mean cost of hospitalisation was $AUD 10261 (95% CI $9205 to $11318).

Conclusion and Future actions

The burden of RSV infection in adults in Queensland is high and similar to other jurisdictions. Age and cardiac disease, immunosuppression and kidney disease are important risk factors for adverse outcomes. This study will continue to recruit for the 2025 RSV season.

Background and Aim
Australian cost estimates of RSV-related disease were limited to ambulatory and inpatient costs from one Melbourne health service in 2018, without accounting for other cost drivers. In Western Australia (WA), additional considerations include higher RSV rates among First Nations children and large geographically remote populations who may require retrieval by the Royal Flying Doctor Service (RFDS) WA.
This study aimed to quantify RSV-hospitalisation costs, aeromedical transport use, and indirect societal costs for parents of children <5 years presenting to emergency with an acute respiratory illness.

Methods and Analysis
We used linked, statewide population data of children hospitalised with RSV from 2015-2024 to measure hospital utilisation costs and RFDS aeromedical transport use. 2022-2023 diagnosis related group cost weights from the National Hospital Cost Data Collection were applied to all years to adjust for inflation.1 Societal costs, including parental missed workdays, were obtained from PATRIC prospective cohort (February 2020-April 2025),2 applying average weekly earnings from the Australian Bureau of Statistics.3
Outcomes
Overall, 224,953 children had 398,627 hospitalisations between 1 July 2015-30 April 2024 (incidence, infants <12 months: 16.4/1,000 child-years). Among RSV-positive episodes, 2,299 (6.2%) required ICU care and 634 (1.9%) involved RFDS transport. Preliminary adjusted mean inpatient costs per child per year were AUD$8,440 in financial year (FY) 2022-2023 (range AUD$7,348 in FY2019-2020 – AUD$11,661 in FY2016-2017). The PATRIC cohort included 1,117 children (median 20 months [IQR: 13-34]); 545 (66%) parents of RSV-positive children missed at least >2 days of work (estimated annual productivity loss of AUD$644 per child).
Conclusions and Future Actions
These are preliminary cost estimates of RSV-hospitalisations in WA. Future cost estimates will apply statistical prediction models to determine under-ascertainment of RSV-hospitalisations.4 These findings support future evaluations of RSV immunisation strategies that will be informed by accurate burden and cost estimates and are essential for guiding policy and investment decisions.
References
1. NWAU calculators | IHACPA
2. Pavlos et al. BMJ open, 14(1), e074308. https://doi.org/10.1136/bmjopen-2023-074308
3. Earnings and working conditions | Australian Bureau of Statistics.
4. Gebremedhin et al. Sci. Rep. 2021;12:232.

Background and aim
In Australia, children <5 years account for most respiratory syncytial virus (RSV)-related hospitalisations, with the highest rates in infants <6 months of age. Nirsevimab is a single-dose, long-acting monoclonal antibody which protects against RSV infection and was introduced in some Australian jurisdictions in 2024. This ecological study aimed to provide a national overview of the early impact of nirsevimab introduction on the burden of RSV in children <5 years of age in Australia.

Methods and analysis
Population-level data on RSV cases and hospitalisations were obtained from the National Notifiable Diseases Surveillance System and stratified by jurisdiction, age and reporting week. This analysis was divided into the pre-introduction (1 April to 31 December 2023) and post-introduction (1 April to 31 December 2024) periods. We visualised weekly and cumulative counts and weekly rates. Incidence rate ratios (IRR) and 95% confidence intervals (CI) were calculated to compare the pre- and post-introduction periods.

Outcomes
Broad population-based nirsevimab programs were introduced in Queensland (QLD) and Western Australia (WA), while other jurisdictions limited nirsevimab for high-risk infants. Nationally, cumulative RSV case numbers increased following nirsevimab introduction, while cumulative RSV-related hospitalisation numbers decreased in infants (0-11 months) but remained similar in other age groups. In jurisdictions with broad population-based programs, IRR was 0.65 (95% CI: 0.60-0.71) for hospitalisations in QLD infants, and 0.61 (0.55-0.68) for cases and 0.41 (0.36-0.46) for hospitalisations in WA infants. Reductions were more pronounced in infants aged 0-5 months compared to 6-11 months.

Conclusion and future actions
As of 2025, both the maternal vaccine (Abrysvo®) and nirsevimab have been introduced in all jurisdictions. It will be important to monitor their effects on the burden of RSV, including among toddlers entering their second RSV season. Characterising the impact of nirsevimab introduction will add to the evidence for immunisation policy considerations, which could improve equitable protection from RSV.

Background and Aim: Nirsevimab, a monoclonal antibody providing passive immunisation against respiratory syncytial virus (RSV), was introduced free of charge for infants in Queensland in April 2024. However, real-world impact data from regional settings remain limited. We assessed the population-level impact of nirsevimab on RSV hospitalisations among infants in Central Queensland.

Methods and Analysis: We conducted a linked cohort and interrupted time series (ITS) analysis using hospital admissions data from 2018 to 2025 linked to the Australian Immunisation Register. Monthly infant RSV admissions were modelled using segmented quasi-Poisson regression with Fourier terms to account for seasonality and Newey–West standard errors to address autocorrelation, with April 2024 specified as the intervention point. Admissions averted were estimated by comparing observed post-rollout counts with projected counterfactual trends based on pre-intervention data.

Outcomes: Between 2018-2025, 739 infant RSV admissions were recorded; 125 occurred after rollout. Overall, 39.1% were aged 0–2 months, 56.1% were male, 24.9% were Indigenous, and 4.7% required ICU admission. Among post-rollout admissions, 16 (13.9%) were vaccinated. Admissions among vaccinated infants increased with time since dose, suggesting possible waning protection (<2 months: 11.1%; >6 months: 44.4%). ITS modelling indicated a trend towards a monthly decline in infant RSV admissions following rollout (IRR 0.95, 95% CI 0.89–1.01), corresponding to an estimated 38 admissions averted, representing a 23.3% reduction over 21 months.

Conclusion and Future actions: Following the introduction of nirsevimab, RSV hospitalisations among infants in Central Queensland declined, with modelling suggesting a meaningful reduction in admissions at the population level. Continued surveillance is warranted to monitor longer-term impact, duration of protection, and differential effects across priority population groups, including Indigenous infants and those at higher clinical risk.

Background and Aim: Respiratory infections are a leading cause of morbidity across the age-spectrum. The advent of new vaccines against SARS-CoV-2 and respiratory syncytial virus (RSV) and encouraging clinical progress on vaccines for human metapneumovirus (hMPV) and parainfluenza (PIV) provide further prevention opportunities. Here we seek to quantify relative age-specific burdens of RSV, hMPV and PIV in comparison to influenza (IFV).

Methods and Analysis: We compiled a data-set using respiratory viral burden studies published from 01/2002–11/2025 and indexed in PubMed. Only studies that reported on medically-attended IFV and at least one of RSV, PIV or hMPV cases by age-group in high-income countries were included, with studies that substantially overlapped with the COVID-19 pandemic excluded. Due to unknown catchment denominators, primary variables were the within-study age-specific ratios of cases of RSV, hMPV or PIV to IFV. For the subset of studies in which all four viruses were included, we conducted a random effects logistic regression to estimate a consensus age-specific ratio of RSV+hMPV+PIV cases to IFV.

Outcomes: Following exclusions and screening, 61 studies were included in the primary analysis comprising >500,000 detections of the 4 viruses. In the regression analysis, the PIV+HMPV+RSV proportion fell from 90% (95%CI 86-93%) to 35% (95%CI 26-44%) as age increased from infants to school-children before rising across adulthood, reaching 60% (95%CI 50-69%) in older adults.

Conclusions and Future Outcomes: We highlight the significant burden of medically-attended illness due to PIV, HMPV and RSV across the age-span, in particular in pre-school children and older adults. Our estimates are relevant to population indications for future combination respiratory vaccines and support the need for effective vaccines targeting this burden. We note, however, significant variations between studies and a need for more comprehensive surveillance of age-specific respiratory virus morbidity.