The climate-induced transmission potential of dengue fever has risen by 48.5% for Aedes albopictus mosquitoes since the 1950s, and 17.0% for Aedes aegypti, according to the 2025 Lancet Countdown on Health and Climate Change. In Latin America, the basic reproduction number for dengue transmitted by A. aegypti has climbed 66%, aligning with the record-breaking outbreaks the region experienced in 2023 and 2024. Globally, dengue caused 7.6 million reported cases in the first months of 2024 alone, and 364 million additional people now live in areas at risk of tick-borne disease transmission compared to the 1950s. The WHO projects an additional 250,000 deaths a year between 2030 and 2050 from malaria, malnutrition, diarrhea and heat stress alone, while a later World Bank assessment raises this number to 800,000.
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Behind those aggregate figures lies a pattern that practitioners know well, but which the wider public rarely sees. When floods submerged a third of Pakistan in mid-2022 and displaced 33 million people, the cameras captured the immediate scenes: families wading through brown water, possessions balanced on heads, villages turned to lakes. The ensuing public health nightmare was less visible. Martin Edlund, co-founder and CEO of BillionScale Health and former CEO of Malaria No More, told us, “there was a five-fold increase in malaria and a ten-fold increase in dengue. Flood-contaminated water caused a cholera outbreak that affected 99,000 people in one district in a single day. Four years later, dengue and malaria rates are still several times what they were before the flood.” Pakistan is not an isolated case. Bangladesh has also experienced floods exacerbating numerouspathogens and antimicrobial resistances, and across the developing world, climate change is reshaping the geography, seasonality and intensity of communicable disease. As Seonmi Choi, Senior Advisor for Climate and Environment at The Global Fund, observes, “climate-related health emergencies force countries to divert scarce resources from long-term development to imminent disasters, falling hardest on populations already most vulnerable.”
As Edlund explains, “a warming world is a playground for the mosquitoes that transmit malaria, dengue, chikungunya, Zika, a whole range of diseases.” The mechanisms are now well documented. Mauricio Santos Vega, Assistant Professor at the Universidad de los Andes and Senior Technical Advisor at the Red Cross Red Crescent Climate Centre, points out that “changes in rainfall patterns create new breeding habitats for mosquitoes, with often dangerous impacts on transmission. Extreme weather events can displace people and overwhelm water and sanitation systems, impacting diseases like dengue, but also causing ecosystem disruptions and more human-wildlife interactions, which can lead to disease spillovers.” Warmer temperatures also accelerate the development of pathogens inside their insect hosts, shortening the time between a mosquito biting an infected human and becoming infectious itself.
New altitudes, new latitudes, new seasons
What was once a tropical and subtropical concern is becoming a wider one. Santos Vega notes that “we have seen new disease-affected areas and resurgences in areas that previously had it under control, especially after natural disasters, but also due to deforestation and other interventions in the environment. In the next decades, rising temperatures will push disease-carrying mosquitoes into higher altitudes, but also higher latitudes, as we’vealready started to see in Southern Europe.” A 2021 Lancet Planetary Health study projects that an additional 4.7 billion people could be at risk of malaria and dengue by 2070, partly because of population growth, but particularly because the mosquitoes are moving into populations without prior exposure.
Practitioners on the ground are already seeing the shift. Dr. Gloria Maimela, CEO of the Foundation for Professional Development (FDP) in South Africa, notes that “we’re getting malaria mosquitoes in areas where they haven’t been before.” Dr. Vidhya Venugopal of the Sri Ramachandra Institute of Higher Education & Research adds another concern: “Dengue, malaria, Zika virus and other vector-borne diseases are not only expanding their range, they’realso mutating more, so we get new strains that may be harder to fight.” This means that while the world is still getting existing diseases under control, the risk of new ones emerging is also rising. At least equally worryingly, melting polar ice, glaciers, and permafrost could cause ancient diseases that have been frozen for millions of years to re-emerge and cause havoc.
The temporal pattern is changing as well as the spatial one. Edlund observes that “you’re also seeing changing weather patterns, lengthening rainy seasons. In many parts of the world, mosquito-borne disease used to be a seasonal phenomenon, and now it’s a year-round phenomenon.” For health systems built around predictable transmission windows, the loss of seasonality removes a key planning assumption. Vector control campaigns, drug stockpiles, hospital staffing and surveillance budgets all become harder to calibrate when the disease no longer takes a break.
Breakthrough solutions are emerging, but systems struggle to catch up
The strain on developing-country health systems is structural. Many were built around historical disease distributions; when dengue arrives in a region where clinicians have never seen it, misdiagnosis and treatment delays can lead to more deaths. Surveillance systems are similarly built for known geographies. Santos Vega argues that the technical capability to do better exists but is unevenly applied: “We have seen significant improvements in surveillance systems in Latin America. But we must link different kinds of data more effectively, for example, satellite-derived climate projections for rainfall and temperature with deforestation patterns and disease surveillance, andthen coordinate these across countries. We need to get better at generating evidence on how specific communities are affected by certain risks, so that responses can be targeted more effectively.” Choi echoes the point: “proven and cost-effective vector-control measures already exist and are being used in many countries, but in a context of increasing climate shocks, best available climate and health data need to be effectively combined to adapt disease control interventions and operationalise climate-informed early warning systems.” Frontline workers, she adds, must be equipped with relevant knowledge and tools to reach the most vulnerable and reduce climate risks to health.
On the solutions side, the news is more hopeful than is often appreciated. Edlund argues that “we’re seeing really transformative technologies come out of the lab and into the field that can bend the curve on burden and cost for many of these challenges.” One of the most promising is Wolbachia, a naturally occurring bacterium found in around a third of all complex life on Earth. When introduced into Aedes aegypti mosquitoes, it shuts down their ability to transmit dengue, Zika, chikungunya and yellow fever. A randomised control trial in Indonesia recorded a 77% reduction in dengue cases and an 86% reduction in dengue hospitalisations, with similar results in other settings. Crucially, the intervention is durable: Wolbachia persists in the wild mosquito population, so the benefits compound over time from a one-off cost, making it highly cost-effective once the initial implementation can be financed at scale.
Financing the response in an age of aid cuts
Even effective tools require capital to scale, and the global health financing landscape is in flux. Western donors are cutting development assistance just as climate-driven disease risk is rising. Edlund argues for a new capital stack built around five C’s: country spending, concessional lending, consumer spending, catalytic grant capital and commercial investment. Grant capital, he notes, now plays a smaller but higher-leverage role: “It’s the de-risking money, which helps to crowd in all the other forms of spending. For example, it helps countries access the low-cost loans they need from regional development banks, and it incentivizes private companies to invest in manufacturing facilities and product improvements that drive down costs.” Regulatory bodies need to keep pace with the technologies, so that countries with scarce resources can adopt new tools quickly rather than waiting years for assessment.
The arc of the next decade is already visible. Disease ranges will keep expanding. Seasons will keep lengthening. Health systems will continue to encounter pathogens for which they were not designed. The question is whether the response, scientific, operational and financial, can match the speed at which the diseases themselves are moving. Santos Vega frames the broader shift required: “We need to see the problems more holistically, with humans embedded in the ecosystem rather than as these independent actors.” The tools to do that, from Wolbachia to integrated surveillance to climate-resilient health financing, exist. The question is whether they will be deployed at the scale and pace the moment demands.
