Explainer: Public health, heat illness & disease vectors — what it is, why it matters, and how to evaluate options

In 2024, Europe recorded 62,775 heat-related deaths across 32 countries—a 23.6% increase from the previous year—while globally, approximately 489,000 people die annually from heat exposure, making extreme heat the deadliest climate hazard on the planet (Nature Medicine, 2025). Simultaneously, climate-driven changes in vector ecology have produced alarming epidemiological shifts: dengue, Zika, and chikungunya cases in Europe surged by 700% compared to the 2010s baseline, with the Asian tiger mosquito (Aedes albopictus) now established in 13 European countries where it was previously absent (ECDC, 2024). These twin crises—thermal stress and vector-borne disease expansion—represent the most immediate and measurable health consequences of climate change, demanding coordinated responses from public health systems, urban planners, and climate adaptation specialists.

Why It Matters

The intersection of extreme heat and vector-borne disease creates a compounding threat multiplier that disproportionately affects vulnerable populations. Heat-related mortality demonstrates stark demographic patterns: during Europe's 2024 summer heatwaves, women experienced 56% higher heat-related mortality than men, with women over 80 bearing the greatest burden (ISGlobal, 2025). Greece recorded the highest mortality rate at 574 deaths per million residents, while Italy's absolute toll exceeded 19,000 deaths in a single season.

The economic implications extend far beyond healthcare costs. The International Labour Organization projects $2.4 trillion in annual productivity losses by 2035 due to heat stress, with outdoor workers in agriculture, construction, and logistics facing the greatest occupational risk. In the United States, farmworkers are 35 times more likely to die from heat stress than the general working population, underscoring the profound equity dimensions of climate-health adaptation.

Vector-borne disease expansion compounds these challenges. Mosquito populations are projected to increase 16-19% under moderate warming scenarios (SSP2-4.5), with a corresponding 25% increase in global mosquito density and 35% rise in dengue incidence by 2050 (Earth's Future, 2025). The first locally acquired dengue infections have now been documented in California, Arizona, West Virginia, and North Carolina—states that historically considered tropical mosquito-borne diseases irrelevant to their public health planning. This geographic expansion into immunologically naive populations with underprepared health systems creates conditions for epidemic amplification that existing surveillance infrastructure is poorly equipped to detect or contain.

Key Concepts

Understanding heat-health and vector-borne disease dynamics requires familiarity with several interconnected domains:

Heat Stress Physiology and Thresholds: The human body maintains thermal equilibrium through evaporative cooling (sweating) and vasodilation. When ambient wet-bulb temperatures exceed 35°C, physiological cooling mechanisms fail regardless of hydration or fitness level. Core body temperature elevation above 40°C constitutes heat stroke, a medical emergency with 10-50% case fatality rates depending on treatment access. The Heat Index and more recently developed HeatRisk metrics attempt to translate meteorological conditions into actionable health risk categories.

Vector Competence and Climate Sensitivity: Disease vectors—primarily mosquitoes (Aedes, Anopheles, Culex species) and ticks (Ixodes)—exhibit temperature-dependent life cycles. Higher temperatures accelerate larval development, reduce the extrinsic incubation period for pathogens within vectors, and extend geographic ranges poleward and to higher elevations. However, extreme heat can also reduce vector survival, creating non-linear relationships between warming and disease transmission.

Urban Heat Island Effect: Cities experience temperatures 2-8°C higher than surrounding rural areas due to impervious surfaces, reduced vegetation, waste heat from buildings and vehicles, and altered airflow patterns. With 68% of the global population projected to live in urban areas by 2050, the urban heat island effect represents a critical determinant of population-level heat exposure.

Heat-Health Action Plans (HHAPs): WHO's framework identifies eight core elements for effective heat response: lead coordination bodies, accurate alert systems, pre-developed communication plans, measures to reduce indoor heat exposure, targeted care for vulnerable populations, health system preparedness, long-term planning integration, and real-time surveillance. As of 2024, 17 European countries have implemented national HHAPs, though coverage and resource allocation vary substantially.

KPI Category	Metric	Baseline Range	Target Range	Measurement Frequency
Mortality	Heat-attributable deaths per million	50-200	<30	Seasonal
Surveillance	ED visits detected within 24h	40-60%	>90%	Real-time
Alert Coverage	Population receiving heat warnings	60-75%	>95%	Per event
Cooling Access	Residents within 15min of cooling center	30-50%	>80%	Annual
Vector Control	Mosquito trap positivity rate	Variable	<5% in endemic zones	Weekly
Response Time	Time from alert to intervention	24-72h	<12h	Per event

What's Working and What Isn't

What's Working

Early Warning Systems with Health Integration: The CDC-NOAA HeatRisk tool, launched in 2024, provides county-level 7-day forecasts with color-coded risk categories specifically calibrated to health outcomes. New York State's integration of HeatRisk forecasts with emergency department syndromic surveillance demonstrated strong correlation between forecast risk levels and actual ED visit rates for heat-related illness during the May-September 2024 season. This real-time feedback loop enables evidence-based resource allocation.

Wearable Physiological Monitoring: Companies like SlateSafety and Kenzen have deployed armband sensors measuring core body temperature, heart rate variability, and hydration status in high-risk occupational settings. The U.S. Army Research Institute of Environmental Medicine has validated chest-strap systems that enable commanders to monitor soldier heat risk in real-time. OSHA-sponsored pilots at construction firms including Rogers-O'Brien in Texas have reduced heat-related incidents by integrating wearable alerts with automated work-rest cycle recommendations.

Community-Based Vector Control: The World Mosquito Program's Wolbachia method—introducing naturally occurring bacteria that reduce mosquito capacity to transmit dengue, Zika, and chikungunya—has demonstrated 77% reduction in dengue incidence in randomized controlled trials in Indonesia. The program now operates across 14 countries with sustained community engagement driving local adoption and maintenance.

Municipal Heat Action Planning: Thane, India's 2024 Heat Action Plan exemplifies best practices by combining ward-level risk mapping (using 1982-2040 climate projections), passive cooling infrastructure investments, and vulnerable population registries. The plan's granular approach—identifying specific neighborhoods with combined high exposure and high vulnerability—enables targeted resource deployment that flat municipal responses cannot achieve.

What Isn't Working

Surveillance Underreporting: Heat deaths remain substantially underreported in official statistics because heat stress exacerbates underlying cardiovascular, respiratory, and renal conditions without being recorded as the proximate cause. Estimates suggest official counts capture only 10-20% of true heat-attributable mortality in many jurisdictions, undermining evidence-based policy and resource allocation.

Fragmented Governance: Heat-health response typically spans meteorological services, public health agencies, emergency management, urban planning, labor departments, and social services—often with no single coordinating authority. This fragmentation produces delayed responses, communication failures, and gaps in vulnerable population coverage. Arizona's 2024 experience, with 4,320 heat-related deaths over the 2013-2024 period despite multiple agency involvement, illustrates coordination challenges.

Equity Gaps in Cooling Access: Air conditioning ownership correlates strongly with income, creating protective disparities. Low-income households, renters, and residents of older housing stock face higher indoor heat exposure precisely when they have fewer resources to adapt. Cooling center strategies often fail to reach the most vulnerable—elderly residents with mobility limitations, homeless populations, and those lacking transportation—who cannot travel to centralized facilities.

Vector Surveillance Lag: Less than 10% of studies documenting mosquito range expansion have performed statistical attribution to climate factors, leaving critical evidence gaps about causation and projection uncertainty (Global Change Biology, 2025). Surveillance systems designed for historically endemic regions lack the infrastructure to detect emergence in newly suitable territories until transmission is already established.

Key Players

Established Leaders

World Health Organization (WHO): Maintains the Heat-Health Action Plan framework adopted by 17+ European countries and provides technical guidance on climate-sensitive disease surveillance. WHO's Global Heat Health Information Network (GHHIN) curates the most comprehensive inventory of national and sub-national heat action plans globally.

U.S. Centers for Disease Control and Prevention (CDC): Operates the HeatRisk forecasting partnership with NOAA, the Heat Tracker syndromic surveillance dashboard, and provides clinical guidance for heat-vulnerable populations. CDC's Climate and Health Program has invested substantially in vector-borne disease surveillance infrastructure since 2020.

Barcelona Institute for Global Health (ISGlobal): Leads the definitive research program on European heat-attributable mortality, producing the annual burden estimates published in Nature Medicine that have shaped EU policy discussions. ISGlobal's methodology—using empirical temperature-mortality relationships across 654 regions—represents the current standard for heat health impact assessment.

World Mosquito Program (WMP): Operates the largest Wolbachia-based vector control program globally, with established operations in Brazil, Indonesia, Vietnam, Colombia, and 10 additional countries. WMP's open-source approach and community engagement model have enabled rapid scaling while maintaining intervention fidelity.

Emerging Startups

SlateSafety: Develops OSHA-sponsored physiological monitoring armbands for occupational heat stress prevention. Real-time core temperature measurement with automated alerts and work-rest recommendations. SOC-2 compliant cloud platform enables fleet-wide workforce monitoring.

Kenzen: Offers predictive wearable safety systems combining heart rate, core temperature, and hydration sensors with machine learning algorithms that provide personalized risk scores and intervention recommendations before symptoms manifest.

MakuSafe: Award-winning wearable connected worker platform with patented heat illness prevention capabilities. Comprehensive analytics dashboard enables enterprise-wide safety monitoring with automated compliance reporting.

VigiLife: Heat stress sensor system ($100-300) released May 2024, combining bicep-mounted wearables with environmental data integration for commercial and industrial applications.

Key Investors & Funders

Breakthrough Energy Ventures: Bill Gates-founded fund with $555 million in committed capital (January 2024 close) investing across climate adaptation including heat resilience technologies and climate-health infrastructure.

7wire Ventures: Healthcare-focused VC firm with explicit climate-health investment thesis, targeting climate-informed care models, remote monitoring for vulnerable populations, and climate risk integration into health systems.

Lowercarbon Capital: Climate tech fund with growing adaptation portfolio including urban cooling, climate-health analytics, and resilience infrastructure.

World Fund: Europe's largest climate VC at $300+ million AUM (April 2024), requiring portfolio companies to demonstrate 100 Mt CO2e per year mitigation potential, with increasing focus on adaptation co-benefits.

Examples

ISGlobal's European Heat Mortality Monitoring System (Barcelona, Spain): ISGlobal's research team, in collaboration with 32 national statistical offices, has built the definitive European heat mortality assessment infrastructure. Their 2025 Nature Medicine publication analyzing 654 regions across Europe provided the 62,775 death estimate for summer 2024, enabling policymakers to quantify intervention urgency. The system's strength lies in its standardized methodology—applying consistent temperature-mortality models with uncertainty quantification—enabling meaningful cross-country comparison. ISGlobal's work has directly influenced EU Adaptation Strategy discussions and member state resource allocation, demonstrating how rigorous academic research can drive policy when designed for decision-relevance from the outset.
World Mosquito Program's Wolbachia Deployment (Yogyakarta, Indonesia): The landmark 2021 randomized controlled trial in Yogyakarta demonstrated 77% reduction in virologically confirmed dengue and 86% reduction in dengue hospitalizations in areas receiving Wolbachia-infected mosquito releases compared to controls. The intervention works because Wolbachia bacteria, once established in local mosquito populations, reduce viral replication within the vector—providing durable protection without ongoing insecticide application. Following the trial, Indonesia's Ministry of Health committed to national scaling, with coverage expanding to 10 million people by 2024. The program exemplifies how rigorous efficacy evidence enables rapid policy adoption when combined with community engagement and ministry partnership.
Thane Municipal Corporation Heat Action Plan (Maharashtra, India): Thane's 2024 Heat Action Plan, developed with the Council on Energy, Environment and Water (CEEW), represents emerging best practice in sub-national heat governance. The plan uses downscaled climate projections (1982-2040) to identify ward-level heat exposure trends, overlaying vulnerability indicators including age demographics, housing quality, and occupational exposure. Specific interventions include cool roof installations, drinking water station placement optimized for vulnerable population access, and an SMS-based warning system reaching 500,000+ residents. Early implementation data shows 40% increase in cooling center utilization and measurable reduction in heat-related emergency calls during May-June 2024 heat events compared to 2023 baseline.

Action Checklist

Conduct heat vulnerability assessment mapping combining climate exposure projections with demographic, housing, and occupational risk factors to identify priority intervention zones
Establish or strengthen syndromic surveillance for heat-related illness through emergency department data sharing agreements and standardized coding protocols
Develop multi-agency coordination mechanism with clear authority, communication protocols, and resource activation triggers spanning meteorological, health, emergency management, and social services
Inventory and expand cooling access infrastructure with explicit equity criteria ensuring coverage for mobility-limited elderly, homeless, and low-income populations
Implement or procure early warning systems with health-calibrated thresholds (e.g., CDC HeatRisk) and establish dissemination channels reaching >95% of target populations
Assess current vector surveillance capacity and expand monitoring infrastructure in areas projected to become climatically suitable for Aedes mosquitoes within 2030 timeframe
Develop clinical guidance and training for healthcare workforce on heat-related illness recognition, treatment protocols, and medication management for heat-vulnerable patients
Establish evaluation framework with pre-defined KPIs (mortality reduction, alert response time, cooling access equity) and annual reporting mechanism

FAQ

Q: How do I know if my region faces significant heat-health risk, and where can I find reliable projections? A: The CDC's HeatRisk tool (wpc.ncep.noaa.gov/heatrisk) provides 7-day county-level forecasts for U.S. locations. For longer-term planning, the Climate Impact Lab and IPCC Working Group II provide regional projections of heat exposure under different emissions scenarios. European regions can access the Copernicus Climate Data Store for downscaled projections. Key indicators to assess include: historical heat-attributable mortality trends (available from national health statistics offices), current urban heat island magnitude (satellite-derived land surface temperature data), and population vulnerability profiles including age demographics and air conditioning prevalence rates.

Q: What is the relationship between heat exposure and vector-borne disease risk, and do they require different response strategies? A: While both are climate-sensitive health threats, they operate on different timescales and require distinct interventions. Heat illness is acute—a 3-day heatwave can produce measurable mortality spikes—demanding rapid-response capabilities including early warning systems, cooling access, and emergency medical surge capacity. Vector-borne disease expansion unfolds over years to decades as mosquito populations establish in newly suitable territories, requiring sustained surveillance investment, community engagement for source reduction, and public health system preparedness before local transmission begins. However, integrated approaches exist: heat waves can increase standing water breeding sites (from emergency water storage or infrastructure failures), and coordinated messaging can address both risks during extreme weather events.

Q: How do wearable heat monitoring technologies compare to traditional occupational safety approaches, and what evidence supports their effectiveness? A: Traditional occupational heat safety relies on environmental monitoring (WBGT measurements) combined with administrative controls (work-rest cycles based on acclimatization and workload intensity). Wearable technologies add individual physiological monitoring—primarily core body temperature estimation from skin sensors—enabling personalized risk assessment that accounts for individual variation in heat tolerance. Published evidence from military deployments demonstrates strong correlation between sensor-detected physiological strain and clinically verified heat illness risk. However, independent validation in civilian workplace conditions remains limited, and adoption barriers include worker privacy concerns, device comfort during physical labor, and integration with existing safety management systems. Cost-effectiveness analyses comparing wearable programs to traditional approaches have not been conclusively established; organizations considering adoption should plan for pilot evaluation before fleet-wide deployment.

Q: What are the most cost-effective interventions for municipalities with limited budgets? A: Evidence suggests several high-impact, lower-cost interventions: (1) Cool roof programs using reflective coatings on public buildings and incentivizing private adoption—Ahmedabad, India's program demonstrated surface temperature reductions of 5°C at modest per-square-meter costs; (2) Urban tree planting in high-exposure neighborhoods, providing shade and evapotranspirative cooling with co-benefits for air quality and property values; (3) Heat-health communication campaigns leveraging existing public health messaging infrastructure; (4) Vulnerable population registries enabling targeted welfare checks during heat events, often implementable through existing social services databases; (5) Cooling center designation in already air-conditioned public facilities (libraries, community centers) requiring primarily signage and extended hours rather than capital investment. Vector control similarly offers cost-effective options including community source reduction campaigns and larviciding of high-risk breeding sites.

Q: How should health systems prepare for vector-borne diseases newly emerging in their regions? A: Preparation should proceed on three tracks. First, surveillance: establish mosquito trapping programs in collaboration with academic entomology departments, with species identification and pathogen testing protocols. Second, clinical preparedness: develop diagnostic algorithms and treatment protocols for relevant diseases (dengue, chikungunya, West Nile), ensure laboratory capacity for confirmatory testing, and train emergency department staff on recognition of unfamiliar presentations. Third, public communication: prepare messaging about personal protective measures, symptom recognition, and care-seeking guidance that can be activated when local transmission is detected. The cost of preparedness is minimal compared to the disruption of managing outbreaks in unprepared systems, as demonstrated by southern Australia's 2024 Japanese encephalitis response challenges.

Sources

Ballester, J., et al. (2025). Heat-related mortality in Europe during 2024 and health emergency forecasting to reduce preventable deaths. Nature Medicine. https://www.nature.com/articles/s41591-025-03954-7
World Health Organization. (2024). Climate change, heat and health fact sheet. https://www.who.int/news-room/fact-sheets/detail/climate-change-heat-and-health
Centers for Disease Control and Prevention. (2025). Vector-borne diseases and climate change. https://www.cdc.gov/climate-health/php/effects/vectors.html
Nair, S., et al. (2025). Increasing mosquito abundance under global warming. Earth's Future. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2024EF005629
European Centre for Disease Prevention and Control. (2024). Aedes mosquitoes surveillance and risk assessment. https://www.ecdc.europa.eu
Global Heat Health Information Network. (2024). Heat action plans inventory. https://heathealth.info/heat-action-plans-and-case-studies/
Anders, K.L., et al. (2021). The AWED trial (Applying Wolbachia to Eliminate Dengue): Efficacy of Wolbachia-infected mosquito deployments. New England Journal of Medicine, 384(18), 1695-1705.
International Labour Organization. (2024). Working on a warmer planet: Heat stress and labour productivity. https://www.ilo.org
PwC. (2024). State of Climate Tech 2024: Climate adaptation and investment trends. https://www.pwc.com/gx/en/issues/esg/climate-tech-investment-adaptation-ai.html