Background and Aim
The 20-valent pneumococcal conjugate vaccine (20vPCV) replaced 13vPCV and 23v pneumococcal polysaccharide vaccine (23vPPV) in September 2025 as the National Immunisation Program (NIP)-funded vaccine for all Australian children with underlying medical risk conditions. Additionally, 15vPCV became available in 2023, and 21vPCV is progressing in the pipeline. We compared the potential vaccine-preventable fractions by serotype of invasive pneumococcal disease (IPD) in children with risk conditions for these PCVs.

Methods and Analysis
We identified from the National Notifiable Disease Surveillance System (NNDSS) IPD cases diagnosed in 2022 and 2023 in children aged <18years with ≥1 risk condition for pneumococcal disease recorded, based on the surveillance definitions that include premature birth, congenital conditions, asplenia, immunocompromise, chronic diseases, and previous IPD. The potential vaccine-preventable fractions were calculated as the proportion of cases due to serotypes in the various pneumococcal vaccines.

Outcomes
Of 1047 cases of IPD aged <18 years, 23% (n=241) had ≥1 risk conditions for pneumococcal disease reported. The most frequently identified serotypes responsible for IPD in these children were 3 (12%), 23B (9%) and 19F (8%). Serotypes in 13vPCV caused 34% of these cases. The incremental preventable fractions of each of the higher valency conjugate vaccines for these cases were 12%, 29%, and 34% for 15vPCV, 20vPCV and 21vPCV, respectively. Incremental gain in vaccine-preventable fraction afforded by 23vPPV beyond the PCVs was 34%, 22%, 5% and 14% for 13vPCV, 15vPCV, 20vPCV, and 21vPCV, respectively.

Conclusion and Future actions
With increasing availability of higher valency conjugate vaccines, it is important to understand the potential benefit these offer. Based on IPD epidemiology alone, the greatest vaccine-preventable fraction for children with risk conditions for pneumococcal disease is afforded by either 20vPCV or 21vPCV, and incremental gain from sequential doses of 23vPCV following 20vPCV or 21vPCV is marginal.

Background and Aim
IPD is a nationally notifiable respiratory disease. Up to 23 strains are preventable through vaccines funded under Australia’s National Immunisation Program (NIP). We examined IPD cases in south-east Melbourne to determine the proportion caused by strains included in NIP vaccines, how many cases had prior vaccination against their infecting strain, and how many involved strains included in the recently introduced Prevenar 20.

Methods and Analysis
Confirmed IPD cases in the SEPHU catchment (2023–2025) were extracted from Victoria’s Public Health Event Surveillance System, including strain, vaccination history, and mortality. Strains were compared with those in Prevenar 7, Prevenar 13, Pneumovax 23 (funded before 2025), and Prevenar 20. Vaccine eligibility was not assessed. Descriptive statistics were calculated.

Outcomes
Of 429 cases, 141 (32.9%) were strains contained in Prevenar 7 and 13, and 99 (23.0%) were strains included only in Prevenar 20 or Pneumovax 23, giving 240 infections (55.9%) potentially covered by Prevenar 20.
Thirty-one infections (7.2%) were caused by strains included only in Pneumovax 23. A further 87 (20.3%) involved strains not included in any of the four vaccines; the most common were 23B1 (17), 23A (11), 31 (8), 6C (8), and 15A/35F (6 each). Seventy-one infections were insufficiently typed for vaccine matching.
Of all cases, 271 involved strains included in vaccines funded before 2025. Only 80 (29.5%) had received prior vaccination against their infecting strain, while 191 (70.4%) had not. Of these 191, 168 were infected with strains included in Prevenar 20, indicating potential future benefit from its availability.

Conclusion and Future actions
These findings quantify cases potentially covered by Prevenar 7, Prevenar 13 and Pneumovax 23, and those potentially preventable with Prevenar 20. They also identify strains not covered by current vaccines, supporting consideration of broader Pneumovax 23 access or additional strains for future Prevenar formulations.

Background and Aim: From September 2022, global rates of invasive group A streptococcal (iGAS) disease surged, exceeding pre-pandemic levels with atypical seasonality particularly affecting children. The effects of the COVID-19 pandemic on iGAS incidence carries important insights into GAS epidemiology and immunology, and can inform disease control strategies, including vaccine development. We previously described the epidemiology of iGAS from mid-2018 to end 2022 from the prospective Paediatric Active Enhanced Diseases network. Here, we provide up-to-date Australian data from 2023 - 2025.

Methods and Analysis: Patients 0 – 18 years with iGAS admitted to six tertiary hospitals in five Australian states/territories were included via laboratory notifications and admission screening. Confirmed cases had GAS isolated from sterile sites; probable cases had septic shock, streptococcal toxic shock syndrome, or necrotising fasciitis and isolation of GAS from a non-sterile site.

Outcomes: In 2023-2025, 479 cases were reported, peaking in 2023 (n = 263), higher than both 2024 (n = 111) and 2025 (n = 105). Severe disease (ICU admission) occurred among 177 (47%) children with 9 deaths. Respiratory virus co-infection was found in 184/327 (56%); of these 142 required ICU admission (77%). Emm1 predominance declined in 2024 and 2025. At discharge, 196 (41%) had not returned to premorbid function. Prophylactic antibiotics were recommended to close contacts of 429 cases (90%).

Conclusion and Future Actions: iGAS incidence peaked in 2023 in sentinel Australian paediatric hospitals. Case numbers in 2024 and 2025 returned to comparable pre-pandemic levels. We demonstrate ongoing morbidity and mortality, and dynamic epidemiology that is influenced by circulating strains and respiratory virus activity, highlighting the urgent need for prevention measures.

Submitted on behalf of the PAEDS Network

Background and Aim
Acute rheumatic fever (ARF) and rheumatic heart disease (RHD) became notifiable conditions in Victoria on 31 July 2023. ARF and RHD are indicators of health inequality, and RHD is an over-represented cause of premature morbidity and mortality in Aboriginal and/or Torres Strait Islander, Māori, and Pacific Islander peoples.

Methods and Analysis
The first two years of notifications recorded in the Victorian Public Health Event Surveillance System (PHESS) showed 37 ARF notifications and 55 RHD notifications.
Analysis of hospital admission data from the Victorian Admitted Episodes Dataset during a similar two-year period, identified 58 admissions with ARF diagnosis codes and 1,034 admissions with RHD diagnosis codes.
Of notifications, five (14%) ARF cases and three (5%) RHD cases identified as Aboriginal. Fourteen (38%) ARF cases and 15 (27%) RHD cases identified as being of Pacific Island descent (Pasifika). This illustrates the over-representation of cases among people who identify as Aboriginal and Pasifika, considering that approximately 1% of the Victorian population identify as Aboriginal and/or Torres Strait Islander, and another 1% are estimated to be Pasifika.

Outcomes
The number of notifications received is below the expected ranges for ARF and RHD in Victoria. Surveillance of these conditions in Victoria is new, and adjustments to the system are required to increase the number of cases being notified.

Conclusions and Future Actions
Consultations with stakeholders, including key notifying clinicians, have identified barriers to notification. Discussions and analysis are ongoing to find areas for improvement in the notification process, with the aim to receive notifications for all ARF and RHD cases in the state, and ensure that they are linked to appropriate care. Coordinated and targeted outreach programs should help to reduce the burden and progression of ARF and RHD among affected groups in Victoria.

Background and Aim:
In Australia, invasive meningococcal disease (IMD) is primarily caused by serogroups B, C, W and Y and is nationally notifiable through the National Notifiable Diseases Surveillance System. Over the past two decades, IMD epidemiology has shifted due to natural fluctuation and the introduction of meningococcal vaccination programs under the National Immunisation Program. This study provides up-to-date analyses of serogroup-specific IMD burden to inform vaccine policy.

Methods and Analysis:
National surveillance data for IMD from 2000–2024 were analysed to assess temporal trends, geographic distribution, demographic and clinical characteristics, and serogroup patterns.

Outcomes:
IMD notification rates declined from a peak of 3.3 per 100,000 population in 2001 to 0.5 per 100,000 in 2023–2024. Young children remain disproportionately affected, accounting for 30% of cases overall. Infants are at highest risk, with overall incidence reaching 18.73 per 100,000 at 3–5 months of age and 13.31 per 100,000 among those aged <1 year (2000–2024). Aboriginal and Torres Strait Islander peoples experienced more than four times the incidence rate of non-Indigenous Australians, with the greatest difference observed among school-aged children (2–14 years).

Serogroup B remains predominant, accounting for 80% of cases in 2024. There is no universally funded vaccine for this serogroup under the National Immunisation Program. Geographical differences persist: the Northern Territory historically recorded the highest rates (12.9 per 100,000 in 2017), while South Australia reported the highest rate in 2024.

IMD remains clinically severe, with 35% of cases requiring ICU admission (2016–2024). Medical risk factors were more common in older adults, while exposure-related risk factors predominated among school-aged children.

Conclusion and future Actions:
National vaccination programs have likely contributed substantially to declining IMD incidence. Strengthening MenB vaccination through universal infant and adolescent programs and improving equitable access for Indigenous communities remain key priorities.

Introduction:
Pertussis remains a public health challenge despite high vaccination coverage. Waning immunity increases reinfection risk. In this study, we compared differences in the time to notification following a previous vaccination or prior infection.
Methods:
We analysed Queensland pertussis notification data from the Notifiable Conditions Systems between 2010 and 2025. Within this period, we compared the median intervals between vaccination-to-notification in vaccinated individuals (most recent vaccination prior to notification) and notification-to-notification in individuals with repeat notifications.
Results:
Between 2010 and 2025, Queensland recorded 59,261 pertussis notifications, of which 41,591 (70%) were PCR confirmed. For this analysis, the 17,670 (30%) non-PCR notifications were excluded.
Over the study period, 41,440 individuals (99.8%) had a single pertussis notification, while 75 individuals (0.2%) had multiple notifications.
Among individuals with prior vaccination and a single notification (n= 27,526), the median interval from the most recent vaccination to notification was 62 months (range: 0–1517). After excluding notifications occurring within 6 months of vaccination (n=1,653), the median interval was 66 months (range: 7–1517).
For individuals with multiple notifications (n = 75), the median interval between the first and second notifications was 68 months (range: 6–171). After excluding those with intervening vaccination, the remaining 69 individuals had a median interval of 65 months (range: 6–168).
There was no statistically significant difference in median time to notification between previously vaccinated individuals (excluding notifications within 6 months) and previously notified individuals without intervening vaccination (p = 0.870).
Conclusion:
In Queensland, repeat PCR-confirmed pertussis notifications were rare over the 15-year period. Time to subsequent notification was similar following prior vaccination or prior infection, indicating comparable protection. These findings align with known waning immunity and support maintaining high vaccine coverage. Integrating vaccination history into surveillance systems will improve interpretation of reinfection patterns and support prevention policy.

Keywords:
Pertussis, Waning Immunity, Reinfection, Surveillance

Background and aim

Diphtheria is a notifiable disease caused by toxigenic Corynebacterium diphtheriae, that primarily involves mucus membranes of the upper respiratory tract (respiratory diphtheria) and non-healing ulcers (cutaneous diphtheria). Notifications are rare because of high vaccination rates with only 6 notifications in the Northern Territory (NT) between 2000-2024. However, in 2025 there were 9 notifications which followed a change in testing practices.

Methods and analysis
We described the epidemiology of diphtheria notifications in the NT in 2025 by age, sex, Indigenous status, specimen type, antibiotic susceptibilities, presenting complaint and vaccination status. We undertook contact tracing and public health action as per Queensland Health Guidelines for Public Health Units for Diphtheria. We described the number of contacts per case and cases identified through contact tracing.

Outcomes
There were 9 notifications; 8 (89%) were Aboriginal people; 6 (67%) were male, all were cutaneous with most 4 (44%) isolated from lower limb wounds. The median age was 40 years (range 16-60 years); 6 (67%) were hospitalised; none died. The median length of hospitalisation was 8 days (range 2 – 18 days); 6 (67%) were macrolide susceptible, 7 (78%) were up to date with vaccinations. The median number of contacts identified per case was 8 (range 1- 30) with 1 case from a correctional facility having 30 contacts; 3 (33%) cases were lost to follow up. No cases were identified through contact tracing.

Conclusions and future actions
We attribute the increase in cutaneous diphtheria notifications to be most likely due to the increased toxin testing of C. diphtheriae isolates. Contact tracing activities in the NT are challenging and resource intensive due to high population mobility. Improved understanding of carriage and transmission and the development of a diphtheria SoNG (Series of National Guidelines) is recommended, as is maintaining high rates of vaccination coverage.

Background and Aim
Buruli ulcer, caused by Mycobacterium ulcerans, has historically been confined to endemic coastal regions in Victoria. In recent years, sustained transmission has emerged in previously non-endemic urban settings, signalling a shift in epidemiology with important implications for surveillance, early detection and public health response. This study aimed to characterise the emergence of Buruli ulcer in two newly endemic urban areas—northwest Melbourne and Geelong—and compare trends with the stably endemic Bellarine Peninsula from 2015 to 2024.

Methods and Analysis
Routinely collected surveillance data were analysed to compare case demographics, lesion characteristics, and delays to presentation and diagnosis across regions. Suburb-level incidence trends were examined to assess the pace and extent of emergence in newly affected urban areas.

Outcomes
Between 2015 and 2024, 485 cases were notified: 195 in northwest Melbourne, 115 in Geelong, and 175 on the Bellarine Peninsula. Cases in the Bellarine were significantly older than those in newly endemic urban areas (p<0.05). Leg lesions were more common in northwest Melbourne (p<0.02), with most cases diagnosed at WHO category I. Presentation delay was longer in northwest Melbourne than in Geelong or the Bellarine (p<0.01). Diagnostic delay was minimal in the Bellarine but significantly longer in both newly endemic areas (p<0.01). Incidence increased markedly in northwest Melbourne, with all newly endemic suburbs exceeding Bellarine incidence in 2023–2024; similar increases were observed in Geelong from 2022 onwards.

Conclusion and Future Actions
The establishment of Buruli ulcer in non-contiguous urban areas represents a growing public health concern. Understanding how M. ulcerans is introduced into new settings requires further investigation. Strengthening systems to detect emerging endemicity and to facilitate prompt risk communication, should be prioritised to reduce diagnostic delay and disease burden. These findings highlight broader lessons for early identification and response to emerging communicable diseases in changing urban and environmental contexts.

Background and Aim
Increasing dengue incidence globally has called for closer monitoring and focused prevention of overseas-acquired dengue cases in NSW. We aimed to describe recent trends in place of acquisition for NSW dengue cases.

Methods and Analysis
NSW-resident dengue notifications were analysed. The five-year mean was calculated using the last 5 non-pandemic financial years (FYs 2016/17-2023/24, excluding 2019/20-2021/22) prior to the last full FY (2024-25). Geographic distribution for the last five years was summarised and compared to FY 2024-25 and 2025-26 year to date (YTD).

Outcomes
The 2024-2025 FY saw the highest dengue incidence ever reported among NSW residents (n=591). This was 1.6x higher than the 5FY mean (362 cases; range 295-480). Across the last 5FYs, NSW cases were most frequently acquired in Indonesia (mean=120), India (mean=47) and Thailand (mean=43). Several Pacific Island countries saw low average NSW-case acquisition, but case numbers fluctuated greatly by country year to year. In 2024-25, Fiji was the second most common place of acquisition among NSW cases (n=96), compared to 5FY mean of only 16 cases. Similar recent fluctuations were seen among cases acquired in the Cook Islands (2025-26 YTD=58 versus 5FY mean of <1 case) and Samoa (2025-26 YTD=32 versus 5FY mean=10 cases) and historically in Vanuatu, the Solomon Islands and Tonga.

Conclusion and future actions
Increasing global dengue incidence is reflected in rising cases among NSW residents. In the context of climate change, vector expansion and global urbanisation, dengue is not “buzzing off”. In NSW, our best tool to meet this challenge is targeted traveller education. Those going to Indonesia, India and Thailand are clear targets for dengue messaging. Prevention efforts among Pacific Islands travellers needs to be more responsive to shifting regional incidence; pro-active monitoring of outbreak reports should focus prevention efforts.

Background and Aim
Australian guidelines changed in 2022 to doxycycline as first line therapy for oropharyngeal or urogenital chlamydia infections, replacing azithromycin, following evidence demonstrating superior efficacy. This study aims to evaluate prescribing patterns before and after the guideline change.

Methods and Analysis
We analysed chlamydia testing and prescribing data from patients 16–80 years that attended a primary care service participating in a surveillance network in Australia January 2015–June 2025. The outcomes were the proportion of positive urogenital or pharyngeal tests prescribed (within -14–30 days of positive test) doxycycline (model 1) or azithromycin (model 2); data were aggregated to calendar-year quarterly intervals. Interrupted time series models assessed the trend in prescribing before the guideline change, at the time of the guideline publication (Q1 2022), and post. Analyses were stratified by service type.

Outcomes
Across 61 clinics, 60,084 people contributed 69,925 positive chlamydia tests. Before the guideline change, each quarter the proportion of positive chlamydia tests prescribed doxycycline increased by 1.61 percentage points (pp) (95% confidence interval (95%CI):1.47–1.75). At the guideline change, there was an immediate 13.5pp increase (95%CI:8.58–18.4), followed by a continued 1.70pp increase per quarter (95%CI:1.08–2.31). Azithromycin prescribing decreased 0.62pp (95%CI:-0.79–-0.44) before the change; immediately decreased 18.1pp (95%CI:-22.75–-13.52) at the change; and continued decreasing by 1.64pp per quarter after the guideline change (95%CI:-2.09–-1.19). The proportion of positive chlamydia tests prescribed doxycycline by sexual health clinics (SHCs) and general practices specialising in the care of gay and bisexual men (GPGBM) in Q1 2015 was 4.87pp and 5.79pp by general practice (GP) and community health (CH). Just before the guideline change at Q4 2021, the proportion prescribed doxycycline by SHCs and GBMGP was 49.0pp and 10.9pp by GP and CH.

Conclusion and Future actions
These findings suggest targeted, setting-specific implementation strategies may accelerate evidence uptake. Future guideline updates should consider how pre-publication dissemination of emerging evidence could be leveraged to support timely management changes across all settings.

Background: Rotavirus (RV) is a leading cause (19.11%) of diarrhoea–related mortality globally. Despite the availability of effective vaccines, RV burden varies substantially across regions, particularly in Southeast Asia and Oceania, with COVID-19 pandemic disruption of immunisation programs further influencing patterns. This study presents burden and temporal trends of RV burden in Southeast Asia and Oceania from 2000 to 2023.
Methods: We analysed Global Burden of Disease (GBD) 2023 estimates to assess RV-attributable incidence, deaths and age-standardised Disability-Adjusted Life Years (DALY) rates.
Results: Age-standardised DALY rates fell markedly between 2000 and 2023, from 545.7 to 127.7 per 100,000 in Southeast Asia and from 304.5 to 148.1 in Oceania. Mortality rates (per 100,000 population) also decreased over this period from 6.6 to 1.4 in Southeast Asia, and from 5.1 to 2.3 in Oceania, punctuated with by modest resurgence in Oceania in 2008-2009 and 2019–2021 with DALY rates rising from 238.9 to 253.7 and 162.5 to 180.5 respectively. Across the 31 countries spanning these two regions, Laos and Myanmar consistently had the highest DALYs rates, while Indonesia surpassed Cambodia as the country with the third highest DALYs from 2019 onwards. Children under-5 had the second highest mortality rates in 2023 (10.0 per 100,000 in both regions) but accounted for the largest estimated number of RV deaths (5,413 and 35, respectively). Adults aged ≥80 years had the highest mortality rates in 2023 (16.6 and 49.9, respectively).
Conclusions: RV burden has declined substantially in South-East Asia and Oceania over the last two decades, with transient increases corresponding to COVID-19 pandemic related immunisation disruptions and an emerging shift in burden towards elderly adults. Persistently high burden in several countries highlights the need to introduce RV vaccination in countries without national programs and to improve coverage in countries with existing programs, alongside catch-up immunisation and enhanced surveillance.