Cohort Study of Arbovirus and Other Emerging Virus Infections in Fiji: AEVI-Fiji Cohort. (AEVI-Fiji)

The AEVI-Fiji Cohort Study: a Longitudinal Study Assessing the Transmission Risk and Dynamics of Mosquito-borne and Respiratory Viruses in Fiji.

Background: Fiji, an archipelago in the South Pacific comprising 332 islands distributed among 4 health administrative divisions (Central, Western, Eastern, Northern), is particularly vulnerable to the (re-)emergence of arboviruses and respiratory viruses due to its sub-tropical climate, the presence of several mosquito vector species, and connections with many countries in the Pacific, Asia and North America. Over the past decades, the epidemiological landscape of arboviruses has shifted from the sequential circulation of each of the four dengue virus (DENV) serotypes to the emergence of Zika virus (ZIKV) and chikungunya virus (CHIKV), concomitantly to the concurrent circulation of multiple DENV serotypes. The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in 2020 significantly challenged Fiji's healthcare system, with the Delta variant alone accounting for approximately 700 deaths, while other respiratory viruses, such as influenza A and B, cause seasonal outbreaks. Despite these threats, comprehensive and up-to-date seroprevalence data remain scarce, limiting the capacity to inform and adapt public health policies.

Methods: The cohort study of Arbovirus and other Emerging Virus Infections in Fiji (AEVI-Fiji cohort study) aims to estimate the prevalence of several arboviruses and respiratory viruses, track the evolution of individual immunity, and analyse transmission dynamics of these viruses within the Fijian population. This longitudinal study will span 38 months and will include about 900 willing participants aged six years and older, recruited from at least 210 households randomly selected across the Central Division. Four visits will be conducted 12 months apart in each household. During each visit, participants will complete a questionnaire capturing their demographic characteristics and history of infections with major arboviruses and respiratory viruses and will provide a blood sample for serological analysis. During the whole study period, participants with a suspected acute infection by an arbovirus or respiratory virus will be screened.

Discussion: For the first time in Fiji, the AEVI-Fiji cohort study will generate longitudinal data to explore the determinants of both arbovirus and respiratory virus infections. The findings are expected to guide targeted public health strategies and enhance preparedness for future infectious disease threats in Fiji and the broader Oceania region.

Study Overview

• Status: Recruiting
• Conditions: Arbovirus Infections; Respiratory Infection Virus
• Intervention / Treatment: Other: Biological samples; Other: Questionnaire

• Study Type: Observational
• Enrollment (Estimated): 910
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Isireli Koroituku, Masters Infectious Diseases; Phone Number: +679 9090729; Email: isireli.koroituku@fnu.ac.fj
• Study Contact Backup: Name: Ahmed Abdouni, PhD, MPH; Phone Number: +689 89527294; Email: aabdouni@ilm.pf

Study Locations

• Fiji
  • Central
    • Suva, Central, Fiji
      • Recruiting
      • Fiji National University
      • Contact: Donald Wilson, MBBS, PhD-Epidemiology; Phone Number: +679 339 4000; Email: donald.wilson@fnu.ac.fj

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child; Adult; Older Adult
• Accepts Healthy Volunteers: Yes

• Sampling Method: Probability Sample

Study Population

The study will specifically target residents of the Central Division of Fiji, which accounts for approximately 42.7% of Fiji's total population. Most inhabitants are located within the Nausori-Lami corridor, a region characterized by a mix of urban, peri-urban, and rural areas. The Central Division is also notable for its ethnic diversity, comprising Indigenous iTaukei, Indo-Fijians, and other minority groups, making it representative of Fiji's broader demographic composition.

Description

Inclusion Criteria:

• Individuals aged 6 years and older who reside in the Central Division of Fiji
• Have lived in the selected household for at least six months at the time of enrollment

Exclusion Criteria:

• Pregnant women;
• Women in labor, or breastfeeding mothers;
• Individuals deprived of liberty by judicial or administrative decision;
• Individuals under psychiatric care or admitted to a health or social care facility for purposes other than participation in the study;
• Adults under legal protection or unable to provide informed consent;
• Homeless individuals;
• Individuals with severe disabilities preventing mobility;
• Individuals unable to understand or complete the study questionnaire

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort

Households members representative of the Fijian population (6 years and older); The study sample comprises randomly selected households from 30 Enumeration Areas (EAs) within the Central Division, selected in proportion to population size to ensure representativeness of the Fijian population. Both urban and rural settings are included. All individuals aged 6 years and above residing for more than 6 months in the selected households are invited to participate in the study.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Level of herd immunity for arboviruses and respiratory viruses by conducting a seroprevalence survey among households including both children and adults In Central division of Fiji	Proportion of participants with Immunoglobulin type G (IgG) antibodies, detected in blood samples : IgG antibodies specific to a panel of arboviruses (including the four DENV serotypes, ZIKV, CHIKV, Ross River virus [RRV], yellow fever virus [YFV], Japanese encephalitis virus [JEV], West Nile virus [WNV]) and respiratory viruses (including influenza viruses A and B, SARS-CoV-2), as well as any major emerging pathogen (pathogen X) will be detected, using a multiplex microsphere immunoassay (MIA). Additionally, seroneutralisation tests will be performed to detect and quantify neutralising antibodies against the same panel of viruses. The IgG and neutralising antibody results for each virus will be combined to determine overall immune response (positive/negative) for the targeted viruses.	From enrollment to the end of the first inclusion visit (V1) at month 12

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Evolution of individual memory immunity for arboviruses and respiratory viruses by performing serological monitoring of the study participants over a period of 38 months	Proportion of participants with Immunoglobulin type G (IgG) antibodies, detected in blood samples : IgG antibodies specific to a panel of arboviruses (including each of the four DENV serotypes, ZIKV, CHIKV, RRV, YFV, JEV, WNV) and respiratory viruses (including influenza viruses A and B, SARS-CoV-2), as well as any major emerging pathogen (pathogen X) will be detected, using a MIA to track changes in antibody composition (seroconversion or seroreversion) and levels (increase, decrease, or stability), as well as possible cross-reaction phenomena. Additionally, seroneutralisation tests will be performed to detect and quantify neutralising antibodies against the same panel of viruses. The IgG and neutralising antibody results for each virus will be combined to determine overall immune response (positive/negative) for the targeted viruses.	From enrollment to the end of the last visit (V4) at month 38
Systematic screening and sequencing of acute infections of the study participants over a period of 38 months	Systematic screening of acute infections for participants to a panel of arboviruses (including each of the four DENV serotypes, ZIKV, CHIKV, RRV, YFV, JEV, WNV) and respiratory viruses (including influenza viruses A and B, SARS-CoV-2), as well as any major emerging pathogen (pathogen X). Positive samples will undergo whole-genome sequencing. This screening and sequencing will allow identification of the viral strain responsible for each infection.	From enrollment to the end of the last visit (V4) at month 38

Collaborators and Investigators

• Sponsor: Fiji National University
• Collaborators: London School of Hygiene and Tropical Medicine; Institut Pasteur; Institut Hospitalo-Universitaire Méditerranée Infection; Ministry of Health, Fiji; Institut Louis Malardé
• Investigators: Principal Investigator: Donald Wilson, MBBS, PhD-Epidemiology, Fiji National University

Study record dates

Study Major Dates

• Study Start (Actual): October 23, 2025
• Primary Completion (Estimated): December 31, 2025
• Study Completion (Estimated): December 31, 2028

Study Registration Dates

• First Submitted: November 13, 2025
• First Submitted That Met QC Criteria: November 13, 2025
• First Posted (Estimated): November 17, 2025

Study Record Updates

• Last Update Posted (Actual): December 1, 2025
• Last Update Submitted That Met QC Criteria: November 24, 2025
• Last Verified: November 1, 2025

More Information

Terms related to this study

• Keywords: Seroprevalence; Respiratory viruses; Longitudinal cohort; Arboviruses; Fiji Islands
• Additional Relevant MeSH Terms: Vector Borne Diseases; Infections; Virus Diseases; Arbovirus Infections; Health Care Quality, Access, and Evaluation; Investigative Techniques; Epidemiologic Methods; Data Collection; Health Care Evaluation Mechanisms; Quality of Health Care; Public Health; Environment and Public Health; Surveys and Questionnaires
• Other Study ID Numbers: FNUHHREC 017.25; FNHRERC 08/25 (Other Identifier: Fiji National Health Research Ethics Review Committee)

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No