A Double Epidemic Is Taking Shape: Malaria Persists, Dengue Expands

The global fight against mosquito-borne disease is splitting into two sharply different battles. Malaria remains overwhelmingly concentrated in poorer countries, where progress has slowed and children continue to bear the heaviest burden. Dengue, meanwhile, is expanding across middle-income, urbanising and climate-sensitive regions, reaching more countries and a broader range of age groups, reveals a new study published in Tropical Medicine and Infectious Disease.

The study "Global, Regional, and National Burden of Malaria and Dengue from 1992 to 2021, with Projections to 2036: An Age–Period–Cohort Analysis," compares the two diseases across 204 countries and territories using Global Burden of Disease 2021 estimates and projects incidence through 2036.

Malaria is being defeated while dengue replaces it. The world may be entering an era of overlapping vector-borne threats: one rooted in persistent deprivation, the other accelerating through urban growth, mobility, climate suitability and weaknesses in conventional mosquito control.

Malaria's Progress Is Real, But It Is Running Out of Momentum

Between 1992 and 2021, the global age-standardised incidence rate fell by an average of 0.55% a year, while the age-standardised rate of disability-adjusted life-years declined by 1.64% annually. These reductions suggest that prevention, diagnosis and treatment have lowered population-level risk and reduced the severity of the disease burden.

However, the absolute number of malaria cases moved in the opposite direction. Estimated cases rose from about 221 million in 1992 to more than 249 million in 2021. Population growth partly explains the increase, but the result is strategically important: falling rates have not translated into a smaller workload for many health systems.

The trend has also been uneven. The study's joinpoint analysis found that malaria incidence declined during much of the 2000s and early 2010s, before rising again between 2014 and 2021. The disability burden also increased during the final years of the study period after a longer decline.

This loss of momentum matters because malaria remains heavily concentrated in countries with the least fiscal and institutional capacity to sustain control programmes. Western sub-Saharan Africa recorded an estimated 137.21 million cases in 2021. Nigeria alone accounted for more than 71 million cases, or 28.61% of the global total. Nigeria, the Democratic Republic of the Congo and Uganda together represented 43.47% of all estimated cases.

The age profile is equally stark. Children younger than five had by far the highest incidence and disability burden. Malaria therefore remains not only an infectious-disease challenge but also a maternal and child health crisis, a poverty issue and a test of primary healthcare delivery. The study's projections reinforce the concern. Global malaria incidence is forecast to fall initially, from 3,485.27 cases per 100,000 in 2021 to 3,207.74 in 2030, before rising again to 3,437.72 in 2036. That would leave the rate only 1.36% below its 2021 level.

The exact forecast is uncertain, but the direction is politically significant. Existing interventions may continue to suppress malaria in the near term, yet insecticide resistance, antimalarial drug resistance, health-system disruption, population displacement and uneven coverage could erode earlier gains. The problem is no longer simply whether malaria tools work. It is whether countries and donors can sustain, adapt and finance them long enough to prevent stagnation.

Dengue Is No Longer a Tropical Side Story

Dengue presents a different and increasingly expansive threat. Estimated cases more than doubled from 28.85 million in 1992 to 58.96 million in 2021. Its age-standardised incidence rate increased by an average of 1.83% annually, while the disability burden rose by 1.29% a year. Unlike malaria, dengue is not concentrated exclusively in the lowest-development settings. Its burden was highest across low-middle- and middle-development regions, particularly Tropical Latin America, South Asia and Southeast Asia.

Tropical Latin America recorded the highest regional incidence rate in 2021, at 5,774.82 cases per 100,000. Southeast Asia had the highest age-standardised disability burden. India alone accounted for an estimated 28.2 million cases—nearly half of the global total—while India, Brazil and Pakistan together represented 74.11% of worldwide cases.

These concentrations create a paradox. A relatively small number of countries could drive substantial global reductions, but those same countries are also undergoing rapid urbanisation, demographic change and expanding regional mobility—conditions that can make dengue harder to control.

The disease is also spreading beyond its traditional geographic boundaries. The study notes growing transmission intensity in Southeast Asia and South America, alongside expansion toward temperate areas in North America and Oceania. Even where current incidence remains low, the appearance of sustained transmission can place new pressure on surveillance systems, blood supplies, hospitals and municipal authorities unfamiliar with dengue control.

The projected trajectory is clearer than for malaria. Global dengue incidence is expected to rise from 752.04 cases per 100,000 in 2021 to 791.31 in 2030 and 831.63 in 2036, an increase of 10.58% over 15 years.

The rise reflects more than mosquito biology. Dengue thrives where rapid urban expansion outpaces drainage, water supply, housing quality and waste management. Household water storage can create breeding sites. Transport networks move infected people and mosquito populations across borders. Climate conditions can extend transmission seasons or make new areas suitable for Aedes mosquitoes.

Dengue is therefore becoming a measure of urban governance as much as public-health performance. Hospitals can treat severe cases, but they cannot compensate for poorly managed water systems, fragmented municipal services or weak outbreak surveillance.

Age and Inequality Are Redrawing the Risk Map

The study compares how age, development and birth cohort shape the two diseases differently. Malaria risk was concentrated in children and declined sharply with age. Dengue displayed a broader distribution, with elevated incidence among adolescents and young adults but also a striking rise among the oldest populations.

The fastest increase in dengue incidence occurred among people aged 95 years and older. Disability rates were also high among young children and older adults. The result challenges the assumption that dengue is primarily a disease of school-age children or young workers.

Ageing populations in dengue-endemic countries could increase the burden of severe disease. Older adults are more likely to have diabetes, cardiovascular conditions, kidney disease or other comorbidities that complicate infection and recovery. Health systems accustomed to treating dengue as an episodic paediatric or young-adult illness may need to revise clinical protocols and preparedness plans.

The age–period–cohort analysis also identified an intergenerational divide. Malaria risk generally declined among birth cohorts after the late 1950s, while dengue risk increased in a stepwise pattern. Later generations are entering environments in which dengue exposure appears increasingly common.

Development level shaped both diseases, but not in identical ways. Malaria had a strong inverse relationship with the Socio-demographic Index, meaning the burden was highest where income, education and demographic development were lowest.

Dengue also showed an inverse association with development, but the relationship was weaker and more complex. Middle-income settings often combine improved connectivity and economic activity with dense urban settlements, uneven municipal services and high human mobility. Development may reduce some health risks while creating new ecological opportunities for dengue transmission.

Economic growth does not automatically produce vector-borne disease control. Unless investment in housing, sanitation, water, surveillance and primary care keeps pace with urban expansion, development may rearrange disease risk rather than eliminate it.

The study also cautions that apparent dengue declines in some low-development settings may reflect weak surveillance rather than genuinely lower transmission. Dengue can be misclassified as malaria or another febrile illness when laboratory testing is limited. Data scarcity is therefore not evidence of safety.

The 2036 Warning: Old Tools Will Not Be Enough

The research does not suggest abandoning established malaria or dengue programmes. It shows why maintaining them without adaptation will be insufficient. For malaria, governments and donors must protect core interventions, bed nets, indoor spraying, rapid diagnostics, effective medicines and preventive treatment, while responding faster to resistance and coverage gaps. Control programmes should be integrated more deeply with maternal and child health, nutrition, community care and local surveillance.

For dengue, the policy response must extend beyond health ministries. Urban planners, water authorities, housing agencies, schools and municipal waste services all influence mosquito breeding and exposure. Outbreak preparedness needs to become part of routine city management rather than an emergency activity triggered only after hospital admissions rise.

New tools could change the projected trajectory. Trials of Wolbachia-infected mosquitoes have demonstrated reductions in confirmed dengue and hospitalisations, while dengue vaccines offer additional protection in selected settings. But their impact will depend on cost, public confidence, regulatory capacity, local serotype patterns and equitable delivery.

The study's forecasts do not explicitly model widespread vaccine adoption, new medicines or major expansion of innovative vector control. The 2036 figures should therefore be read as conditional warnings rather than fixed outcomes. They show what could happen if recent patterns persist, not what must happen.

The research notes that it relies on GBD estimates, which are shaped by the quality of underlying national data. Reporting, diagnostic access and surveillance completeness vary widely. Dengue estimates may differ from official case counts, particularly in countries where laboratory confirmation is limited.

Age–period–cohort modelling also has inherent statistical constraints, while estimates for the oldest dengue age groups may be less stable because cases are sparse. The projections do not directly incorporate future climate scenarios, intervention scale-up or sudden changes in health policy.

Nevertheless, the strategic conclusion is difficult to ignore. Malaria and dengue cannot be treated as interchangeable mosquito problems. Malaria remains an entrenched inequality crisis in low-resource settings. Dengue is becoming a wider urban and climatic threat that can intensify even as countries grow wealthier.