Dengue In The Pacific Region – Expert Q&A

Scoop

04-06-2025

Press Release – Science Media Centre
The SMC asked experts about the current situation in the Pacific.
The Cook Islands declared a dengue outbreak in Rarotonga last week.
Other Pacific nations including Sāmoa, Tonga, and Fiji are also experiencing outbreaks.
The SMC asked experts about the current situation in the Pacific.
Dr Gregor Devine, Senior Director, Field Entomology at the World Mosquito Program, comments:
What is the immediate threat posed by dengue in the wider Pacific region, and how is this changing?
'Dengue fever is the world's most prevalent disease spread by mosquitoes. Cases are increasing across the Western Pacific (e.g., Pacific Island Countries and Territories, Laos, Cambodia, Vietnam) and South East Asia (e.g., Bangladesh, Indonesia, Thailand, and Timor-Leste). All of these countries experienced significant dengue outbreaks in 2024 and 2025, and the general trend in cases globally is relentlessly upwards.
'These increases are fuelled by 1) climate change (increased temperatures encourage mosquito proliferation and shorten the time needed for viruses to replicate in their mosquito hosts), 2) increasing globalisation (and the increased movement of humans carrying the virus), 3) immunological naïveté, where human populations are being exposed to new dengue serotypes, and 4) the limited impact of existing control measures.
'According to the Pacific Syndromic Surveillance System, as of May 27th 2025, dengue cases are increasing or peaking in Fiji, Samoa, Tonga, Kiribati, and Cook Islands. There have been deaths reported from Fiji, Tonga and Samoa.'
What hopes are currently on the horizon for new technologies or programmes to combat the disease?
'Current responses to dengue outbreaks largely involve the application of insecticides and the implementation of environmental 'clean-up' campaigns, but these have limited impacts. Moreover, resistance to insecticides is increasingly documented in the Pacific, and this further reduces the impact of conventional vector control.
'A safe, effective and sustainable solution exists. The Wolbachia method, developed by the non-profit World Mosquito Program, involves releasing mosquitoes infected with a bacteria that reduces their ability to transmit dengue. It has been proven to have a tremendous impact on dengue transmission around the world. Wolbachia releases have been piloted in Fiji, Vanuatu, Kiribati, and New Caledonia. Following six years of Wolbachia mosquito releases in New Caledonia, the project has been hailed a monumental success, and the French territory hasn't had a dengue epidemic since 2019. This year, releases will continue in Kiribati, and be adopted in Timor-Leste.'
What is your biggest concern and/or is there anything you wish people understood better about the situation?
'The upward trend in dengue case numbers regionally will inevitably stress public health systems and impact family well-being (through both the health and economic costs of hospitalisation and the lost earnings of the sick). Sustainable ways to combat dengue, such as the Wolbachia method, are desperately needed. Vaccines are still years away from being universally affordable and applicable.'
Conflict of interest statement: Greg Devine is the Senior Director of Field Entomology for the World Mosquito Program
Dr Joan Ingram, Medical Advisor, Immunisation Advisory Centre, comments:
What is the immediate threat posed by dengue in the Pacific region, and how is this changing?
'Dengue outbreaks are currently affecting Kiribati, Samoa, Fiji, Tonga and French Polynesia with the most cases being reported from Fiji, according to The Pacific Community (SPC). Case numbers are increasing in all of those areas, apart from in French Polynesia. There are four dengue serotypes – and both serotype 1 and serotype 2 are currently circulating.
'The Pacific Islands are vulnerable to dengue outbreaks as they have high levels of mosquitoes and dengue viruses can be introduced by infected people.
'Between 2012 and 2021, there were 69 outbreaks of dengue fever among the Pacific Islands. However, they are not unique in having dengue fever – dengue is common in many other regions including the Americas, Africa, the Middle East and Asia.
'Globally, dengue cases were at a very high level in 2024, particularly in South America. Cases increased almost 30-fold there between 2000 and 2024. Urbanisation, globalisation and climate change have contributed to this increase.'
What is your biggest concern and is there anything you wish people understood better about the situation?
'Dengue is often a leading cause of fever in risk countries. Estimates are that around 6 in 1000 travellers spending a month in a risk area become unwell with dengue, with up to 30% of them being hospitalised.
'Dengue is spread by common biting mosquitoes (various Aedes species), which thrive where humans live. The main way to avoid dengue is mosquito bite avoidance. Aedes mosquitoes (unlike the malaria-transmitting Anopheles) are daytime feeders, with two peak times of biting activity in the day – 2 to 3 hours after dawn, and mid-to-late afternoon. However, they may feed all day indoors or on overcast days.
'People should regularly apply effective repellent as well as using light-coloured clothing to cover up. In addition, they should take steps to reduce mosquitoes indoors (such as screens on windows and doors), and in the environment by emptying any water-holding containers.'
What hopes are currently on the horizon for new technologies or programmes to combat the disease?
'Qdenga, a dengue vaccine, is available in 30 countries overseas but not in New Zealand. It protects against dengue serotype 1 and 2 very well, especially in people who have had previous dengue. Protection against serotypes 3 and 4 is still being evaluated.
'An earlier dengue vaccine increased the risk of severe dengue in people who had not had dengue previously. It does not seem as though Qdenga does that, but it is still being monitored and most authorities prefer to administer it to people with past dengue infection although the guidelines differ.
'A new hope for the future is the use of Wolbachia-infected Aedes aegypti. Wolbachia infection blocks the transmission of the dengue virus from mosquitoes. Trials are ongoing with promising results.'
No conflicts of interest.
Dr Berlin Kafoa, Director, Public Health Division at The Pacific Community (SPC), comments:
What is the immediate threat posed by dengue in the Pacific region, and how is this changing?
' 1. Increasing morbidity due to escalating dengue outbreaks reported across the Pacific region with circulation of multiple serotypes.
'Dengue is actively circulating in at least six Pacific Island Countries and Territories (PICTs), including Fiji (>8,000 cases, 4 deaths), Tonga (793 cases, 3 deaths), French Polynesia (>2,000 cases), Samoa (110 cases, 1 death), Cook Islands, and Kiribati. Multiple serotypes (DENV-1, DENV-2, DENV-3) are co-circulating, increasing the risk of severe dengue due to secondary infections in populations with partial immunity.
' 2. Changing epidemiology and vulnerable populations
'There is a growing incidence of severe dengue amongst children and youth with no prior dengue exposure. There are older adults coming from areas historically free of dengue. This suggests immunity gaps, but the lack of updated seroprevalence data limits precise risk profiling.
' 3. Climate and mobility as amplifiers
'Climate change and variability (e.g., rainfall, temperature) is expanding mosquito habitats and altering transmission patterns.Increased regional and international travel and trade from endemic areas (e.g., Southeast Asia, South America) raises the risk of virus introduction.'
What hopes are currently on the horizon for new technologies or programmes to combat the disease?
' 1. A need for collaboration across sectors, agencies, and countries.
'Through the Pacific Public Health Surveillance Network (PPHSN), we are working with WHO and allied members to support countries with preparedness, detection and response to dengue and other arboviral diseases. This includes:
Rapid risk assessments and technical guidance
Laboratory supplies and testing algorithms and Strengthening PCR testing capabilities in countries.
Subtyping and WGS/Whole-Genome Sequencing via reference labs (e.g., VIDRL in Australia).
Dissemination of risk communication messages through multiple channels and sharing of best practices in risk communication and community engagement
' 2. A need for predictive analytics and early warning
'We are exploring predictive algorithms that integrate climate data (e.g., rainfall, temperature), flight and mobility data, and historical outbreak and seroprevalence data. These tools aim to forecast outbreak risks and optimize vector control timing.'
' 3. Vector control capacity building to promote a One Health approach.
'The Pacific Vector Network (PVN) launched in 2023, a service arm of PPHSN, supports a coordinated response to control of vector-borne disease in the region; practical entomology training for PICTs; mosquito surveys, mapping, and surveillance; and provision of vector control equipment and insecticides.'
' 4. New tools being tested
'Other new tools being tested in the region include pilot testing of new technologies such as Sterile Insect Technique (SIT) in French Polynesia, and trials of Wolbachia introduction in Fiji, Vanuatu, New Caledonia, and Kiribati. For possible consideration, there is the introduction of dengue vaccines-contingent on availability of sero-prevalence data.'
What is your biggest concern and/or is there anything you wish people understood better?
'The real risk of severe dengue is rising. Severe cases and fatalities are being reported, especially among youth. Dengue should not be dismissed as a mild illness, it can be life-threatening.
'There are gaps in immunity and surveillance. Many populations remain immunologically naive due to limited past exposure. Inadequate seroprevalence data and diagnostic capacity hinder targeted responses.
'There are changes in vector behaviours with possible increase in behaviours resistance to insecticides.
'Dengue is not the only arboviral threat which further complicates surveillance, diagnosis, and response efforts. Other threats include:
Zika: Imported cases have been reported in the Pacific Rim (e.g., New Zealand from Fiji).
Chikungunya: A major outbreak in La Réunion (339,000+ cases) and an imported case in Wallis and Futuna.
Yellow fever: While not yet reported in the Pacific, the presence of Aedes vectors makes introduction a real risk
'There is a need to support the Pacific to acquire new technology for genomic surveillance. Genetic sequencing of dengue strains is essential to track virus movement and mutations across the region, but capacity remains limited.
'Dengue is no longer a seasonal or isolated threat in the Pacific; it is a regional health emergency shaped by climate, mobility, and historical vulnerabilities. Through a One Health multisector, multiagency and multi-country collaborative efforts with WHO, PIHOA and PPHSN partners, we are responding and building the tools and intelligence to predict, prepare and hopefully prevent the next wave.'