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Abstract
Introduction Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus that causes encephalitis and other morbidity in Southeast Asia. Since February 2022, geographically dispersed JEV human, animal and vector detections occurred on the Australian mainland for the first time. This study will determine the prevalence of JEV-specific antibodies in human blood with a focus on populations at high risk of JEV exposure and determine risk factors associated with JEV seropositivity by location, age, occupation and other factors.
Method Samples are collected using two approaches: from routine blood donors (4153 samples), and active collections targeting high-risk populations (convenience sampling). Consent-based sampling for the latter includes a participant questionnaire on demographic, vaccination and exposure data. Samples are tested for JEV-specific total antibody using a defined epitope-blocking ELISA, and total antibody to Australian endemic flaviviruses Murray Valley encephalitis and Kunjin viruses.
Analysis Two analytic approaches will occur: descriptive estimates of seroprevalence and multivariable logistic regression using Bayesian hierarchical models. Descriptive analyses will include unadjusted analysis of raw data with exclusions for JEV-endemic country of birth, travel to JEV-endemic countries, prior JEV-vaccination, and sex-standardised and age-standardised analyses. Multivariable logistic regression will determine which risk factors are associated with JEV seropositivity likely due to recent transmission within Australia and the relative contribution of each factor when accounting for effects within the model.
Ethics National Mutual Acceptance ethical approval was obtained from the Sydney Children’s Hospitals Network Human Research Ethics Committee (HREC). Local approvals were planned to be sought in each jurisdiction, as per local ethics processes. Ethical approval was also obtained from the Australian Red Cross Lifeblood HREC.
Dissemination Findings will be communicated to participants and their communities, and human and animal health stakeholders and policy-makers iteratively and after final analyses. Understanding human infection rates will inform procurement and targeted allocation of limited JEV vaccine, and public health strategies and communication campaigns, to at-risk populations.
- Surveys and Questionnaires
- Epidemiology
- VIROLOGY
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STRENGTHS AND LIMITATIONS OF THIS STUDY
The study establishes a framework for a national semiharmonised approach to collections occurring across multiple states and territories and will provide the first estimates of Japanese encephalitis virus (JEV)-specific antibody seroprevalence in Australia.
Administration of a questionnaire to actively enrolled participants allows identification of risk factors for JEV infection.
Limited evidence informing the prior extent of JEV transmission across large geographical areas of Australia means selecting sample populations is challenging.
Selection and sample biases that may limit representativeness and generalisability to the general population.
Differing recruitment strategies limit the ability to make comparisons between blood donor and active collections.
Introduction
Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus endemic to the Asia-Pacific region transmitted by Culex species mosquitoes. Wading birds are a natural viral reservoir and pigs act as amplifying hosts. Humans are dead-end hosts due to the insufficient viraemia to infect mosquitoes, and direct human-to-human transmission is not known to occur. Human JEV infection results in mild or asymptomatic disease in most cases, and encephalitis occurs in approximately 1 in 250–1000 human infections.1–3 JEV infection is vaccine-preventable and JEV vaccine was included in the national immunisation programmes of 12 Asian countries by 2016.4
Despite proximity to Asia, JEV had never been endemic in Australia. Apart from overseas travel acquired infections, rare episodic human case detections in the Torres Strait Islands (TSI) of Australia (between the Australian mainland and Papua New Guinea) and in Northern Australia (figure 1A) have occurred: three people in the TSI in 1995, and one person in the TSI and one in the Cape York Peninsula in 1998; and one in the Tiwi Islands in 2021.5 For this reason, Australia did not have population-based vaccination recommendations. JEV vaccine was only recommended for laboratory workers who may be exposed to JEV, periodically for people who live or work on the outer TSI and for travellers spending 1 month or more in endemic areas of Asia during virus transmission season.6
(A) Map of Australian Climate classification, reproduced with data from the Australian Bureau of Meteorology16 and (B) location of collection sites for proposed active collections and blood donor centres by risk classification. Conduct of all active serosurveys is subject to local ethics approval.
In February 2022, the unexpected detection of JEV in diseased domestic (farmed) pig foetuses led to rapid expansion of testing for JEV in piggeries, human encephalitis cases and in vector populations.7–9 JEV was detected in over 80 commercial piggeries in 2022 across the south-east states of Victoria, New South Wales, South Australia and in southern Queensland.10 In 2022, there were 4300 registered pig production sites in Australia,11 with approximately 2.4 million pigs. The first human case on the mainland was reported on 3 March 2022 in Queensland.12 From 1 January 2021 to 5 January 2023, 45 human clinical JEV infections, mostly encephalitis, have been notified in Australia, with seven deaths.
In addition to domestic pigs, feral pig populations are established throughout a wide geographical range in north and eastern Australia, and in parts of the south and west.13 JEV has been detected by nucleic acid amplification and/or JEV-specific antibody testing in feral pigs in the Northern Territory and Queensland.10 All JEV sequences from humans, animals or vectors have been genotype IV,14 and have a close phylogenetic relationship with JEV found in human and pig cases in Indonesia in 2017 and 2019 and and the isolated case of encephalitis in a Tiwi Islands resident in January 2021.15 This suggests likely transmission from north to southern Australia dating back to early 2021, but the precise timing and pathway remain unclear.
Australia consists of six states, New South Wales, Victoria, Queensland, Western Australia, South Australia and Tasmania and two internal territories, Northern Territory and the Australian Capital Territory. The land mass is vast (7.7 million km2) with a population of 25.7 million, mainly residing in south and east coastal fringes. Wide climate zone ranges exist; tropical regions in the north, an arid desert interior, and temperate regions in the south (figure 1A).16–18 The introduction and spread of JEV across Australia was likely precipitated by La Niña weather patterns, established in late-November 2021 and continuing until May 2022. This brought above average rainfall to much of the eastern states and numerous flooding events, favouring opportunistic dispersal of migratory wading birds and increases in mosquito populations. Culex annulirostris is the major vector for JEV and is active year-round in northern Australia. In the southern mainland C. annulirostris populations peak in summer (December–February) and disappear during winter months (June–August).7 It is not present in the island state of Tasmania.
Emergence of JEV across almost one-third of the Australian continent represents an entirely novel situation posing risk to human health. It resulted in a One Health national outbreak response19 that included enhanced surveillance and studies in various potentially infected species to determine the extent and timing of virus transmission. Data to anticipate if and how JEV transmission may persist in Australia’s unique ecology and in the largely immunological naïve human population (which differs with Asian countries) is needed. As many more people are typically infected with JEV than detected by clinical case-based surveillance,6 7 serological testing for JEV-specific antibodies is key to ascertain the extent, characteristics and patterns of recent infection in the Australian human population. This will complement serosurveys conducted in pigs and other animals.
We developed a national cross-sectional serological survey for JEV-specific antibodies focussing on populations with the highest likelihood of being infected with JEV recently and to compare this with serological evidence of past infection from other flaviviruses endemic in Australia, Murray Valley encephalitis virus (MVEV) and Kunjin virus (KUNV).
Methods
Study design
We designed a series of multimodal cross-sectional human seroprevalence surveys to occur following the 2021–2022 summer in targeted high-risk and control populations of all ages in all six Australian states and the Northern Territory. The study protocol was developed from April to June 2022, with input from researchers, animal, vector and human disease specialists and public health officials, as well as senior chief health and veterinary officials from state, territory and national governments. The study aims to recruit between June 2022 and July 2024 to ensure adequate time for local jurisdictions are to engage the community and mobilise staff. Opportunistic and pragmatic approaches to serosurvey design were taken due to challenges in conducting studies across a large geographic range of rural and remote Australia in small, dispersed populations and accounted for availability of skilled study personnel. Active collections, described below, were planned with, and co-led by, local state and territory health departments.
Objectives
The study aims to understand the human epidemiology of JEV infection in Australia. Specific objectives are to:
Determine the prevalence of JEV-specific antibodies in blood (seroprevalence) nationally with a focus on populations in areas of high risk of JEV exposure (as defined by human, animal and mosquito detections) in people of different age groups.
Determine risk factors associated with JEV seropositivity such as geographical location, age and occupation.
Patient and public involvement
The public were not involved in the design of the study. The study was designed with state, territory and national governments and local public health units.
Study population and locations
Sample collection is via two approaches: (1) blood donor collection: using blood samples collected from blood donors in different risk areas, and (2) active collection: community-based recruitment and sampling of individuals in risk areas based on geographical, recreational and occupational risk groups, including active and opportunistic sampling (table 1).
Locations, recruitment strategy and target populations of JEV active consent-based collection serosurveys
Blood donor collection
In Australia, the national provider of blood and blood products is Australian Red Cross Lifeblood (Lifeblood). Eligible blood donors can donate blood through fixed, and pop-up/mobile donor centres. Fixed location centres are permanent and located in larger towns and cities while pop-up/mobile centres are in major towns and cities in areas where fixed centres are not present or in more regional or rural parts of the country on a rotational roster. Fixed location donor centres that correlated geographically with JEV-infected piggeries in New South Wales and Victoria were selected for sampling (figure 1B). Fixed location donor centres in Queensland, South Australia, Western Australia and the Northern Territory are generally confined to large coastal towns with donors not representative of the inland rural populations located near infected piggeries and thus, are not included. In South Australia, sampling is from pop-up or mobile donor centres in high-risk areas along the Murray River, as well as a lower-risk metropolitan Adelaide. Tasmania has had no human, animal or vector detections, and no competent JEV vector,20 making local virus transmission unlikely. Tasmania and metropolitan Adelaide were used as comparator sites to explore background seroprevalence of JEV-specific antibodies related to past vaccination or infection acquired overseas.
Donors are aged ≥18 years and meet donor eligibility criteria, as per Lifeblood requirements.21
Active collections
Active collections are proposed for populations with geographical distribution mirroring locations of human, animal and vector detections in the Northern Territory, Queensland, New South Wales, Victoria, South Australia and Western Australia (table 1, figure 1B) subject to local ethics approval. Recruitment strategy was designed and dependent on feasibility after discussions with local investigators. All active collections are consent based and include administration of a questionnaire to participants.
Sample size
The expected seroprevalence of JEV-specific antibodies is unknown as no prior Australian population-based studies have been done, nor comparable studies performed internationally in similar previously immune-naïve populations. We assume that the expected seroprevalence in risk areas is likely to be <10% based on the following factors: virus transmission in Australia was likely only during one summer season5 22; the low number of human cases detected,23 limited vector flight range from reservoirs,7 small human populations in near vicinity to vector/animal detections; and small proportions of the resident populations in targeted areas who likely lived in JEV endemic areas or had been vaccinated previously.
Approaches to sample size calculations differed between blood donor and active collections. The blood donor sample calculations aimed to detect a minimum difference between seroprevalence in high-risk and low-risk donor centre locations, acknowledging that some seropositive samples were expected in low-risk donor centres due to prior infection overseas and/or prior vaccination. In active collections, a target sample size was calculated based on a desired precision, without comparison to a control sample.
Blood donor collection
Sample size is limited by expected donor attendance (table 2), with minimum detectable differences calculated based on Lifeblood’s recent data (table 3). A 2-week sampling period was also chosen to avoid repeat sampling of plasma donors (plasma can be donated every 2 weeks in Australia). Based on expected donor turnout data, it will be feasible to collect approximately 4153 samples, with the aim of including 3912 samples in the analysis after exclusions based on JEV-endemic (estimated proportion 1.1%–3.8% from Australian Bureau of Statistics data24) or missing country of birth (conservative proportion 15% based on historical Lifeblood data). This sample size was determined to be adequate based on the calculated minimum statistically significant difference at this sample size between high-risk and low-risk sites (table 2) at different hypothetical levels of control site seroprevalence.
Sample numbers by locations based on donor attendance in March 2022 and anticipated exclusions for JEV-endemic or missing country of birth
Minimum detectable difference in JEV seroprevalence between control and high-risk locations at different levels of control site seroprevalence, with 80% power and 95% confidence level, blood donor collection
Active collections
Active recruitment of participants in sparsely populated regional and remote areas where JEV has been detected will be challenging; however, low seroprevalence can still be detected with smaller sample sizes. A maximum target sample size was calculated for each collection occurring over a collection period of 1 month.
While a low seroprevalence (<10%) was still expected, noting these were residents living in virus detection areas, when calculating target sample size for each collection, we based calculations on a higher seroprevalence of 50% as this produces the most conservative (largest) estimate of required sample size. Additionally, a 95% confidence level, desired power of 80% and a design effect of 3 are used as per the following equation:
Due to challenges in achieving adequate fixed sample sizes, recruitment is aimed to be via convenience sampling, with the potential to extend the collection period over additional weeks and increase community engagement strategies (during periods of low/no-virus transmission) if there is slow accrual of participants. Table 4 highlights margins of error (95% CI) at different levels of hypothetical seroprevalence using two fixed sample sizes.
Margins of error (95% CI) at different levels of hypothetical seroprevalence using two fixed sample sizes
Consent
Blood donor collection
Blood donors in Australia consent to blood being taken for research purposes as part of routine donation consent. Additionally, we obtained a waiver of consent to collect a 6 mL sample of blood in a serum-separating tube from all donors during routine blood donation.
Active collections
Informed consent is obtained using electronic consent forms from participants actively recruited to participate. Everyone within a target resident population in specified risk areas was invited to participate.
Sample transport and testing
Sample transport
Samples are transported from collection sites to the laboratory using cold storage boxes by pathology couriers. Samples are centrifuged prior to transport to reference laboratories. Samples are stored at 4°C for up to 14 days, or frozen at −20°C until testing; they are to be stored thereafter for a minimum of 5 years from the publication date of the study results.
Serological testing
Accurate serological testing for flaviviruses can be challenging due to broad cross-reactivity between individual flaviviruses in many assays (particularly immunofluorescent antibody assays and binding ELISAs) and due to anamnestic antibody responses to various flaviviruses being triggered by infection or vaccination with another flavivirus.25 In interrogating serological responses to individual flaviviruses, the highest specificity can be achieved by measurement of neutralising antibody, but neutralising antibody assays are not suitable for large-scale testing due to being labour intensive, low-throughput and involving handling of live virus requiring a high level of biosafety. Defined epitope-blocking (DEB) ELISAs achieve the high specificity associated with neutralising antibody assays while being amenable to automation are therefore less labour intensive,26 and can be performed using standard biosafety precautions. This high specificity of DEB-ELISAs is achieved by incorporating a monoclonal blocking antibody which has been shown to bind to an epitope highly specific to the flavivirus of interest, but not to other flavivirus species.27 28
All samples, except those from the Victorian active collection, are tested centrally at the Institute of Clinical Pathology and Medical Research (ICPMR) in Sydney, New South Wales, using an in-house DEB-ELISA for JEV-specific total antibody, in which ≥40% inhibition has been validated as representing a positive reaction. This enables comparability of results across all samples from different states and territories. The antibody is a murine monoclonal antibody designated 989. It detects a neutralising epitope in the JEV envelope protein. The assay was evaluated against neutralisation in the following groups: 1000 JE neutralising antibody negative sera, 300 JE NT antibody positive sera (IgM negative), 20 JE IgM positive sera, 150 sera positive for MVE neutralising antibody, 150 sera positive for Kunjin neutralising antibody, 10 Kunjin IgM positive sera and 5 MVE IgM positive sera. In addition, 230 people undertaking JE vaccine courses were tested prevaccination and post vaccination for both neutralisation and ELISA antibody. The results of the evaluation showed a specificity of 100% and a sensitivity of 98.5% compared with viral neutralisation. They found no cross-reaction with MVE or KUNV.29 The Victorian Department of Health wishes to ensure rapid preliminary results be obtained, and have opted to test samples from the Victorian active collection locally at the Victorian Infectious Diseases Reference Laboratory (VIDRL) using a Euroimmun immunofluorescence assay (IFA) for IgM and IgG. The Euroimmun IFA is a quantitative assay that detects JEV IgG/M against JEV whole virus (genotype I Nakayama strain), using fluorescein-labelled anti-human IgG/M on BIOCHIP slides fixed with JEV-infected and non-infected cells.30 Samples positive on this assay will be sent to ICPMR for confirmatory testing on the DEB-ELISA.
Samples undergo screening using the JEV DEB-ELISA at a 1:10 dilution (figure 2). Negative samples are considered JEV seronegative. Positive samples are serially diluted to obtain a quantitative JEV-specific total antibody titre and undergo further testing by IFA for JEV-specific IgM. Qualitative (positive/negative) and quantitative (titre) results are reported. A JEV-positive result can indicate a true JEV infection or vaccination. Cross-reaction from other flaviviruses may give a positive JEV result, but the likelihood is low given the assay uses a monoclonal antibody specific to JEV. In South-eastern Australia, regular epidemics of MVEV and KUNV infection have occurred since first recognised in 1917. Five previous seroprevalence studies for MVEV have been undertaken in Victoria and New South Wales from 1976 to 2011, with seroprevalence ranging from 0.8% to 14%.31–34 Therefore, positive JEV DEB-ELISA samples will undergo secondary testing for MVEV and KUNV-specific antibodies, and antibody levels compared with those from the JEV DEB-ELISA; if significant concordance in seropositivity is found, testing of JEV positive samples for antibody for MVEV and KUNV-specific antibodies may also be undertaken. This aims to aid in the interpretation of JEV-seropositive results.
Laboratory testing protocol flow chart for all samples. DEB, defined epitope-blocking; ICPMR, Institute of Clinical Pathology and Medical Research; IFA, immunofluorescent assay; JEV, Japanese encephalitis virus; MVEV, Murray Valley encephalitis virus; VIC, Victoria.
Study resources
A generic head protocol was developed, detailing procedures for consent-based and waiver-of-consent collections, with generic adult and child participant information sheets and consent forms. As new collections are planned, brief protocols with collection-specific information not already included in the head protocol are added as appendices to the head protocol for expedited ethical review.
Survey participant questionnaire
Administration of a questionnaire is not feasible for blood donor participants; operational constraints necessitate a waiver of consent for recruitment.
Active collections include a questionnaire (online supplemental material) requesting information on:
Supplemental material
Demographics, including age and sex, and contact details (required for laboratory processing and testing and to enable results to be provided to the participants).
Potential for JEV exposure-related risk, such as contact with pigs and waterbirds, bodies of water, and mosquitoes, occupation, outdoor recreation, and personal protective behaviours.
History of JEV vaccination, travel or residence/birth in a JEV-endemic country.
Questionnaires are delivered via a REDCap or Microsoft Forms or paper-based forms.
All study resources, including the questionnaire, can be modified for local contexts and specific study populations; however, a core set of identical questions are included in all questionnaires.
Data management
Access to the study data is granted only to the named investigators specific to each collection. Deidentified line-listed data are stored on a secure health server for analysis. Data collected for this research will not be transferred to any other organisation or used for any other purpose other than those stated in this protocol. Only deidentified aggregate results of seroprevalence are to be presented and/or published. Active collection sites in respective states and territories are also able to publish and use data for public health messaging purposes at local levels during the study. All study data are stored on secure jurisdictional health servers. Demographic data (blood donor collection) and questionnaire data (active collections) are sent to the study team and linked to laboratory results via unique identifiers.
Blood donor collection tubes are labelled with only a unique number, and active collection tubes are labelled with initials, date of birth and study number.
Feedback of participant results
For the active collection, individual results with appropriate clinical interpretation, are to be provided via email or telephone to the participants (or parent/guardians) by the research team. Seropositive participants are informed that their blood has detectable antibodies, which may have been acquired recently or from past travel or vaccination. If IgM positive, participants are supported to have a clinical assessment and advised to have convalescent serology undertaken. All participants receive an information sheet that explains their result, as well as public health messaging around mosquito bite prevention. As JEV is a notifiable disease in Australia, cases with positive JEV serology may be notified to the National Notifiable Diseases Surveillance System.
No feedback of results is provided to blood donors as the samples are deidentified under a waiver of consent.
Outcomes and statistical analysis plan
The primary outcome is JEV total antibody seropositivity, estimated with associated degree of uncertainty, overall and by subgroup (eg, age stratum, sex, state, collection site) separately for the blood donor and active collections. JEV seropositivity can be due to either recent JEV infection within Australia, or due to other reasons, such as JEV infection acquired overseas and past JEV vaccination. Therefore, a secondary outcome is to estimate JEV seropositivity due to recent transmission within Australia while excluding other reasons for JEV seropositivity. If sufficient positive results, estimations of the total seropositive proportion positive for IgM will also be reported.
Two approaches described below will be taken to estimate primary and secondary outcomes:
Descriptive estimates of seroprevalence.
Multivariable logistic regression using Bayesian hierarchical models.
Descriptive estimates of seroprevalence
In line with objective 1, three approaches to JEV seropositivity estimations will assess prevalence of JEV-specific antibodies nationally, and by subgroup based on age stratum, sex, state, collection site and so on, with additional analysis for participants in active collections.
Unadjusted estimates from raw data
Mean JEV seropositivity with 95% Clopper-Pearson CIs will be estimated for each variable category from raw data. Clopper-Pearson intervals were selected as they are appropriate for prevalence estimates close to 0%, and low JEV seroprevalence is expected.
Estimates with exclusions applied
Exclusions will be applied to raw data to exclude JEV-seropositive cases likely related to overseas JEV infection and vaccination.
For both the blood donor and active collections these will variously include:
Country of birth has widespread or presumed widespread JEV transmission (Bangladesh, Brunei, Burma, Myanmar, Cambodia, China, India, Indonesia, Japan, Laos, Malaysia, Nepal, North Korea, South Korea, Papua New Guinea, Philippines, Sri Lanka, Taiwan, Thailand, Timor-Leste, Vietnam).
Country of birth with presumed transmission in focal areas (Bhutan, Pakistan, Russia, Singapore, Macau, Hong Kong, Mongolia).
JEV vaccination reported.
Following these exclusions, other variables considered for exclusion will include:
Missing/unknown country of birth.
Participant unsure whether they received a JEV vaccination.
Member of defence force (blood donor only).
History of travel to a JEV-endemic country.
If JEV seropositivity among participants with these characteristics is found to be significantly greater than those without these characteristics on χ2 tests of homogeneity, they will be considered for exclusion.
Following exclusions, the mean JEV seropositivity due to recent infection within Australia will be estimated with 95% Clopper-Pearson CIs overall and by subgroup.
Standardised estimates of data after exclusions have been applied
The age and sex distribution of samples obtained through blood donor and active collections may not be representative of the target population. To improve generalisability of estimates, the JEV seroprevalence estimates will be standardised to age and sex distributions at state and territory level.
Multivariable logistic regression using Bayesian hierarchical models
In line with objective 2, multivariable logistic regression models will be fit to the active collection datasets with exclusions applied, to determine: (1) which risk factors are associated with JEV seropositivity due to recent transmission within Australia, including demographic factors such as age, sex and location, exposures such as proximity to animals and water, and mitigating effects of personal protective behaviours; (2) the relative contribution of each factor towards this outcome when accounting for the effects of other factors within the model.
For the blood donor collection, individual donor information on JEV vaccination is not reliably available; thus, information on the JEV vaccination rate at the time of sample donation of the participant’s Statistical Area 3 (SA3) area of donation will be used as a proxy for the probability of the individual having been vaccinated against JEV, accounting for likely correlation between JEV vaccination and travel to a JEV-endemic country and/or membership of a defence club. Therefore, known donor factors such age and sex will be nested among area-level estimates based on information about their geographic area of donation (at SA3 level). A hierarchical Bayesian framework for modelling problems with multiple levels of effect will be used to model these nested effects.
For active collection samples collected in Victoria first analysed using the IFA at VIDRL, later confirmatory testing will be undertaken using JEV DEB-ELISA at ICPMR. However, residual effects from differences in test characteristics based on testing centre may remain. Therefore, for the active collection model, individual participant factors will be nested among centre-level effects and modelled using a hierarchical Bayesian framework.
For both blood donor and active collection models, a stepwise backwards elimination and forward addition approach will be applied to select covariates that are substantively associated with the outcome for inclusion in the model. Covariates will be deemed substantively correlated if their 95% credible intervals for the OR does not include zero. Model convergence will be checked using trace plots, trace rank plots, Monte Carlo error and number of effective samples.
Ethics
National Mutual Acceptance (NMA) ethical approval was obtained from the Sydney Children’s Hospital Network Human Research Ethics Committee (HREC). NMA is a national system for scientific and ethical review of human research projects conducted in publicly-funded health services across jurisdictions.35 Local ethical approvals were sought in each jurisdiction, with review expedited due to the NMA.
Additionally, blood donor collections were approved by the Lifeblood HREC.
Dissemination
As testing will be done on a rolling basis as samples are provided, any potential interim and all final analyses will be provided to all key stakeholders, including but not limited to national and jurisdictional health departments and chief health and veterinary officers, the Communicable Diseases Network Australia, the Australian Technical Advisory Group on Immunisation, and the Department of Agriculture, Water and Environment. These data will inform priority populations for vaccination, vaccine procurement and programme rollout strategies, and other public health interventions. The study results will be presented according to the Strengthening the Reporting of Observational Studies in Epidemiology recommendation for cross sectional studies and submitted to a peer-review medical journal.
Data will also be used as inputs into modelling studies, together with estimates of infection (JEV active infection and/or seropositivity) in animal and vector populations derived from surveillance and special studies in these hosts and data on climate and other environmental factors, to assess past and predict future JEV transmission in Australia.
Outcomes of the study with appropriate language and messaging strategies will be shared with active collection participants and their communities, as well as disseminated nationally via publication on government websites, and so on. Reports are paired with public health messaging materials on JEV vaccination and prevention of mosquito bites.
Limitations
This study has several limitations. Active collections using opportunistic and convenience recruitment have inherent selection biases that may limit representativeness and generalisability to the general population. Similarly, the blood donor population is known to have a higher average income and education level and are healthier than the general population and may not reflect populations in rural/remote areas, reducing representativeness. As active collection sampling strategies will differ across jurisdictions due to local factors, this may limit comparisons between collections. JEV vaccination was not routinely recorded in the Australian Immunisation Register prior to 2022; thus, participants reported vaccination history may be subject to recall bias, and for blood donors, only limited information on country of birth, travel and vaccination is available.
Despite these limitations, valuable information on the feasibility of conduct and initial results from this work on a national scale in the uniquely vast context of Australia will inform future serological and wider seroprevalence studies and are anticipated to inform the one-health approach to control of JEV transmission and disease in Australia and any other settings where this virus may emerge in the future.
Ethics statements
Patient consent for publication
Acknowledgments
We would like to acknowledge the Australian Japanese encephalitis virus serosurvey group: Lambert S, Wood N, Snelling T, Bakar S, Glasgow K, Hope K, Baldwin Z, Luscombe C, Friedman D, Marsland MJ, Thomson T, O’Brien H, Williamson D, Lim C, Kitchener S, Ratsch A, Chor J, Skyes A, Khandaker G, Smoll N, Walker J, Currie B, Nelson J, Hinchcliff A, Krause V, Worley P and Hayward C.
Australian governments fund Australian Red Cross Lifeblood to provide blood, blood products and services to the Australian community.
Supplementary materials
Supplementary Data
This web only file has been produced by the BMJ Publishing Group from an electronic file supplied by the author(s) and has not been edited for content.
Footnotes
Collaborators Japanese encephalitis serosurvey group: Stephen Lambert, Deborah Williamson, Jannah Baker, Tom Snelling, Keira Glasgow, Kirsty Hope, Chloe Luscombe, Adriana Notaras, Zoe Baldwin, Jennifer Case, Tilda Thomson, Madeleine Marsland, Helen O’Brien, N. Deborah Friedman, Heidi Carroll, Candice Holland, Scott Kitchener, Angela Ratsch, Josette Chor, Alice Sykes, Gulam Khandaker, Nicolas Smoll, Jacina Walker, Liam Flynn, Vicki Krause, Aleena Williams, Alexandra Hinchcliff, Jane Nelson, Bart Currie, Louise Flood, Rebecca Beazley, Nicola Spurrier, Carmen Hayward, Paul Worley.
Contributors The study design and concept were conceived by NEW, AK and KM. NEW, AK, GK and SP wrote study documents and ethics applications. RH, VH, IBG and DOI codesigned the blood donor component. LH, MO, JK and DED designed the laboratory testing algorithm and LH developed the assay utilised. JB wrote the statistical analysis plan. All authors contributed to the drafting of the manuscript.
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Competing interests None declared.
Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
Provenance and peer review Not commissioned; externally peer reviewed.
Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.