2024 is the worst year for dengue cases on record. As of July 23, over 10 million cases of dengue have been reported from 176 countries across all WHO regions (although the Americas account for most cases), with more than 24,000 severe cases and 6,508 deaths. This figure already surpasses the number of cases in 2023, which was also a record year.
There is no doubt that dengue, a vector-borne disease caused by four serologically related viruses, is a major infectious disease threat to health. Over the past two decades, there has been a tenfold increase in reported cases, and even this figure is likely an underestimate.
It is the only infectious disease for which annual mortality is rising (80% of infections are asymptomatic or produce mild febrile illness but the case fatality rate increases during outbreaks). Rightly so, WHO has classified dengue as a grade 3 emergency (ie, requiring a major to maximal WHO response). Upcoming monsoons in the tropics and northern hemisphere are likely to drive a steep increase in dengue cases over the coming months.
The surge in cases and the geographical expansion of the virus are, in many ways, man-made. The triad of urbanisation, climate change, and the movement of people and goods is facilitating the spread of dengue and its Aedes mosquito vector. More extreme El Niño and La Niña events have led to heavy precipitation, humidity, and rising temperatures favouring vector reproduction and virus transmission.
The 2023 Lancet Countdown on health and climate change estimated that rising temperature alone has already increased the global transmission potential of Aedes aegypti by 42.7% between the 1950s and the 2010s, with the impact expected to increase further in the future. As virus cocirculation increases, so too will the risk of secondary infections, and with that, also the risk of more severe dengue, hospitalisations, and deaths.
An emerging concern is Africa, where active transmission of dengue virus has been reported in 15 countries in the past year. The continent has little clinical experience with the disease, many primary infections go undetected, and funding constraints hinder preparedness and response.
Already, 50% of the population lives in unplanned urban settings, a proportion due to rise to 62% by 2050. Mitigation measures to tackle dengue upfront as part of urban development will be crucial. Following a severe outbreak in Burkina Faso in 2023, and the declines in malaria cases, which would have masked dengue in the past, there is far more awareness of dengue and of the need to address response and reporting.
But generally, dengue does not receive anywhere near the attention and resources it merits. Outbreaks can overwhelm health systems and inflict a huge economic burden, yet limited WHO funds for dengue control come from the Director General’s Emergency Fund, and further funding from countries has not been forthcoming. The seasonality of dengue and the periodic nature of outbreaks means that control measures are often implemented reactively, during the peak in cases—too little, too late. A WHO resolution on dengue to get the much-needed commitment of countries to address this growing problem would be one positive step. Countries should be encouraged to propose such a draft ahead of the 2025 WHO Executive Board Meeting.
If the spread of dengue virus is to be halted, there needs to be a shift from ad-hoc responses to isolated outbreaks towards long-term, integrated programming between relevant sectors. An increase in funding is required for a combination of dengue programmes that include prevention, management and treatment, and effective surveillance.
Embedding dengue prevention in urban planning is a key health measure in climate change adaptation. Several exciting new dengue control technologies, not least new vaccines, should be able to help with prevention (although less likely with control) of dengue outbreaks.
Together, such measures offer a way for controlling, and then reversing, the spread of dengue. When such programming also includes community-level initiatives, it can lead to sustainable behaviour change that results in positive effects on health outcomes. Many benefits would extend to other arboviruses, such as chikungunya and the newly emerging Oropouche virus.
How exactly can we best address the immediate threat of current outbreaks while tackling the longer-term headwinds of climate change, urbanisation, and increased mobility that will continue to drive dengue? What co-benefits might be gleaned? A Lancet Commission on dengue and other Aedes-transmitted viral diseases will attempt to answer these questions. But what is clear is the need for a multipronged and multidisciplinary approach; there is no easy solution to dengue.