Public health researchers released new evidence on October 10, 2024, linking the resurgence of several infectious diseases in multiple regions to the direct and indirect effects of climate change, drawing together observational data, ecological studies, and modelling work to build a clearer picture of how a warming world is reshaping the epidemiological landscape. The findings, presented across a coordinated set of peer-reviewed publications and briefed jointly by major public health institutions and climate research organisations, describe a pattern that is increasingly difficult to explain without reference to climate — and that, researchers argue, demands a matching response in surveillance, preparedness, and health-system adaptation.

The diseases highlighted in the new research span a broad range. Vector-borne diseases including dengue, chikungunya, malaria, and Lyme disease have been expanding their geographic range and intensifying in some of their established territories. Waterborne diseases including cholera and specific gastrointestinal infections have been flaring in regions affected by floods, drought, or both. Zoonotic diseases — those that are transmitted from animals to humans — have been emerging with greater frequency and in locations that in some cases had not previously been at significant risk. And specific respiratory infections have been shown to respond in complex ways to changes in temperature, humidity, and air quality that are associated with the broader climate shift.

The Evidence Base

Today's research draws on several complementary lines of evidence. Long-term epidemiological surveillance data, available for many diseases over several decades, have been analysed to identify trends and to test whether observed changes are consistent with climate-driven explanations. Ecological studies have documented shifts in the range and abundance of disease vectors — including mosquitoes, ticks, and other arthropods — that can be linked to specific climate variables. Genomic analyses have tracked the evolution and spread of specific pathogens, helping to understand how microbes themselves are responding to changing conditions. And mathematical and statistical models have been used to project how these trends may develop over coming years and decades under different climate scenarios.

The integration of these lines of evidence has allowed researchers to move beyond general statements about the link between climate and health to more specific, quantitative, and policy-relevant findings. For individual diseases, researchers have been able to attribute specific proportions of recent trends to climate drivers, to identify specific mechanisms by which climate change is affecting disease dynamics, and to project the likely future trajectory under alternative climate scenarios. For the broader pattern, the cumulative weight of evidence makes the climate-health connection increasingly difficult to dismiss as coincidental.

Vector-Borne Diseases

Vector-borne diseases have been a particular focus of today's research, and for good reason. Many of these diseases depend on specific combinations of temperature, humidity, and rainfall for their transmission, and their geographic distribution is therefore inherently sensitive to climate. As temperatures have risen in temperate regions, and as rainfall patterns have shifted in tropical and sub-tropical areas, the conditions favourable for specific vectors — and for the transmission cycles they support — have expanded and intensified.

Dengue, in particular, has been an important indicator of the changing epidemiological landscape. Cases of dengue have been rising in many established endemic areas and have been documented in locations previously thought to be at the edge of the vector's range. In Europe, in parts of the United States, and in other regions with historically limited dengue transmission, specific outbreaks and autochthonous — locally transmitted — cases have been documented in recent years. The precise attribution of these cases to climate is complex, with travel, urbanisation, and other factors also playing roles, but the broad pattern is consistent with what climate projections have long anticipated.

Malaria, the subject of enormous historical effort, has continued its decline in many regions but has shown concerning signs of resurgence in others. Highland regions previously protected by cool temperatures have in some cases become newly suitable for transmission. Specific outbreaks in areas where the disease had been effectively controlled have renewed attention to the importance of sustained surveillance and intervention, and climate-related shifts in vector distribution have featured in analyses of these outbreaks.

Tick-borne diseases, including Lyme disease and several others, have been expanding their range in temperate regions as conditions have become more favourable for the ticks that transmit them. Warmer winters allow more ticks to survive, longer active seasons expose humans and animals to greater cumulative risk, and specific shifts in the distribution of host animals contribute to the overall pattern. Cases have been reported in regions where the diseases were previously rare or absent, and public health authorities in those regions have been adjusting surveillance and clinical awareness accordingly.

Waterborne and Diarrhoeal Diseases

Waterborne diseases have been affected by climate change through multiple pathways. Heavy rainfall and flooding can overwhelm sanitation systems, contaminate water sources, and create conditions favourable for the spread of pathogens including cholera and various enteric bacteria and viruses. Drought can reduce water availability, concentrate pathogens in remaining supplies, and produce conditions in which hygiene practices are compromised. Rising temperatures can affect the growth and survival of specific pathogens in environmental reservoirs, and ocean warming has been linked to the expanded range of species of Vibrio bacteria, which include the causative agents of cholera and other human infections.

Cholera, in particular, has been the subject of concerning recent developments. Outbreaks in multiple regions have been larger, more persistent, and in some cases more severe than in recent comparable periods. While the immediate drivers of individual outbreaks include conflict, displacement, and weakness of public health systems, the broader pattern of increased cholera activity has been linked, in part, to climate-driven changes in the environmental conditions favourable for the pathogen and its transmission.

Diarrhoeal diseases more broadly remain a major source of illness and death, particularly in children in low-income countries, and the climate-sensitive component of their epidemiology is an important part of the broader public health picture. Specific analyses in today's research suggest that climate change is likely to increase the burden of diarrhoeal disease in coming decades, absent significant compensating progress in sanitation, water supply, and primary health care.

Zoonotic and Emerging Diseases

The potential for zoonotic diseases to emerge and spread in ways influenced by climate change has been a particular area of attention. Changes in land use, in agricultural practices, in the distribution of wildlife, and in specific ecological conditions can all affect the likelihood of pathogens crossing from animals to humans. Climate change affects many of these underlying factors, and the cumulative effect is to alter the risk landscape for emerging zoonoses.

Today's research includes specific case studies of zoonotic diseases whose emergence or spread has been linked to climate drivers. Hantavirus infections associated with specific rodent population dynamics. Rift Valley fever outbreaks associated with patterns of rainfall and flooding in affected regions. Avian influenza outbreaks in wild bird populations whose movements and distributions are shifting. And specific fungal infections whose geographic range appears to be expanding in ways consistent with climate change.

The broader concern, which runs through much of the research, is not any single disease but the cumulative effect of climate-driven changes on the overall risk of emerging infectious disease events. The recognition that the frequency and severity of such events is not simply random but is shaped by specific ecological and environmental conditions has been growing, and the implications for pandemic preparedness are significant.

Respiratory Infections and Air Quality

Respiratory infections have been affected by climate change in less obvious but increasingly well-documented ways. Specific respiratory viruses, including influenza and other common seasonal pathogens, have seasonality patterns that depend on temperature and humidity, and shifting climate conditions have been associated with changes in the timing, duration, and intensity of respiratory virus seasons. Pollen seasons have been extending and intensifying, affecting respiratory conditions including asthma and contributing indirectly to susceptibility to infection.

Air quality has been a particular focus. Wildfires, whose frequency and intensity have been rising in many regions under climate change, produce air pollution that affects respiratory health over wide areas and can increase susceptibility to infection. Dust storms, increasingly associated with drought in specific regions, can carry pathogens and allergens over long distances and contribute to respiratory illness. The interaction between air quality and respiratory infection is an active area of research, and today's findings add specific detail to the picture.

Health Systems Under Pressure

The cumulative effect of these climate-sensitive changes in disease patterns is significant pressure on health systems. Many of the affected diseases require specific diagnostic capacity, treatment protocols, and public health response measures that may not be well established in regions newly affected. Health workforces that have not historically needed expertise in specific diseases may lack the training and experience to recognise and manage them promptly. Laboratory networks, referral systems, and public communication infrastructures may require significant adaptation.

Today's research emphasises that the health response to climate change is not only about the direct health impacts of heat, extreme weather, and air pollution — important though those are — but also about the shifting infectious disease landscape that climate change is producing. Specific recommendations include the strengthening of disease surveillance, investment in laboratory capacity, training of health workers in climate-sensitive diseases, expansion of vector control and environmental management, integration of climate information into public health practice, and specific attention to populations and regions at particular risk.

The Broader Climate-Health Connection

The findings released today fit within a much broader body of work on climate change and health that has been developing for more than two decades. The World Health Organization, major national public health agencies, and independent research institutions have consistently identified health as one of the most immediate and important domains in which the consequences of climate change are already being felt. Heat-related illness and death, extreme weather impacts, food and water insecurity, mental health effects, and the infectious disease dimensions described in today's research all feature in this broader picture.

What has been changing is the specificity and confidence of the evidence. Earlier generations of climate-health research often depended on broad projections and qualitative analyses. The current generation is able to draw on rich observational data, sophisticated analytical methods, and increasingly well-validated models to provide quantitative, location-specific, and policy-relevant findings. This evolution has not produced a new message so much as a sharper and more urgent version of a message that has been accumulating for some time.

Mitigation and Adaptation

The policy implications of climate-health research run in two directions. Mitigation — reducing the greenhouse gas emissions that drive climate change — is the foundational response, and one that matters not only for climate outcomes but for health outcomes as well. The health co-benefits of emissions reduction are substantial: cleaner air from reduced fossil fuel combustion, more active lifestyles supported by shifts in transport infrastructure, improved diets associated with reduced consumption of emissions-intensive foods, and many others. These co-benefits have been an increasingly prominent feature of public health advocacy for climate action.

Adaptation — adjusting health systems, infrastructure, and practices to the climate impacts that are already inevitable — is the complementary response. Today's research underscores that adaptation for infectious disease specifically is an important and under-resourced area, and that the scale and speed of required investments will need to increase. National adaptation plans in many countries have been incorporating health considerations more explicitly, and specific funding mechanisms have begun to support health adaptation activities, but the overall pace remains well below what the research community argues is needed.

A Message for Policymakers and the Public

For policymakers, the message from today's research is direct. Climate change is not only a long-term environmental issue; it is an immediate and evolving public health challenge. Policy responses need to reflect this reality, through sustained investment in the health systems that will have to manage the changing disease landscape, through integration of climate considerations into public health planning and practice, and through the broader climate mitigation and adaptation effort that shapes the trajectory of future health risks.

For the public, the message is one of context for developments that may be observed in daily life. The expansion of specific diseases into new regions, the emergence of new infectious threats, and the intensification of familiar diseases in altered ways are not random events but are increasingly part of a coherent climate-driven pattern. Public awareness of this pattern, and support for the policies and practices needed to address it, is part of what the broader response requires.

Looking Ahead

Today's research will be added to the growing evidence base on climate and health, and it will inform ongoing assessments, policy processes, and operational decisions in many countries and international bodies. Additional research is continuing across many fronts, including efforts to sharpen the attribution of specific disease trends to climate, to improve projections of future risks, and to evaluate the effectiveness of specific adaptation measures.

The underlying relationship between climate and infectious disease is unlikely to become simpler in the years ahead. But the evidence on which policy decisions can be made is becoming clearer, and the tools available to respond are becoming more refined. What happens in the coming decade — in terms of emissions, of adaptation investment, of health system strengthening, and of the specific disease trajectories that unfold — will determine whether the trends documented today are addressed with the seriousness they deserve.

The researchers releasing today's findings have been measured in their presentation. They have been clear about uncertainty where it exists, about limits to what specific lines of evidence can say, and about the continuing need for better data, better models, and better surveillance. But on the broader point — that climate change is reshaping the infectious disease landscape in ways that demand attention and action — their message has been consistent and clear.