Dengue

What it is

Dengue is a mosquito-borne viral disease caused by four antigenically distinct serotypes: DENV-1, DENV-2, DENV-3, and DENV-4, transmitted almost exclusively by Aedes aegypti, an urban mosquito that breeds in small containers of standing water. A first infection with one serotype confers lasting immunity to that type but leaves the patient more vulnerable to severe disease on re-exposure to a different serotype. This antibody-dependent enhancement mechanism makes dengue uniquely dangerous in endemic zones where multiple serotypes co-circulate. Severe dengue, formerly called dengue hemorrhagic fever, causes plasma leakage, hemorrhage, and organ failure; untreated, case fatality exceeds 2-5%. Key institutional players include WHO and its regional arm PAHO, national health ministries across South and Southeast Asia and Latin America, and two vaccine makers: Takeda Pharmaceuticals (Qdenga/TAK-003) and Sanofi Pasteur (Dengvaxia).

History

Epidemic dengue was first documented in the 1770s-1780s across Asia, Africa, and North America. The four serotypes were characterized in the 1940s and 1950s; dengue hemorrhagic fever was identified as a distinct clinical syndrome in Thailand and the Philippines in the same era. Through the 1970s the disease was endemic in only about nine countries. Urbanization, population growth, and global trade expanded Aedes aegypti's range rapidly, and by 2010 dengue was endemic in over 100 countries. Sanofi's Dengvaxia, licensed in 2015 in several countries, was restricted in 2017 after post-approval data showed it increased severe-disease risk in previously-uninfected recipients, dealing a lasting blow to vaccine confidence in affected countries, particularly the Philippines. In September 2023, WHO recommended Takeda's Qdenga (TAK-003) for routine immunization in children ages 6-16 in high-transmission settings, without requiring pre-vaccination serostatus screening, removing the chief barrier that had complicated Dengvaxia's rollout. WHO prequalified Qdenga in May 2024.

Current state

2024 set a recorded global high: WHO logged over 14.4 million cases and more than 12,000 deaths across 100+ countries. The Americas accounted for over 90% of global cases, with Brazil alone reporting 10 million-plus cases and 6,321 deaths. Indonesia reported 88,593 confirmed cases through April 2024, roughly triple the prior-year pace. Globally, estimated actual infections run 100-400 million annually, of which only a fraction are laboratory-confirmed. As of mid-2026, dengue remained hyperendemic across South and Southeast Asia and Latin America. Sri Lanka's 2026 surge (see 斯里兰卡迎来数年来最严重的登革热年，6月感染人数几近翻倍，累计超过44,000例) tracked toward the island's 2019 record of 105,000 cases, driven by Aedes breeding sites left in cyclone debris compounded by southwest monsoon flooding. Climate change is widening the endemic zone: autochthonous dengue has been documented in mainland France, Italy, and Spain, and Aedes albopictus is now established across much of southern Europe.

Relationships

Dengue shares its primary vector with yellow fever, Zika, and chikungunya, so vector-control decisions are rarely disease-specific and outbreaks often run concurrently. The pattern recurring most visibly in 2025-2026 is post-disaster dengue: cyclone debris or flood residue seeds Aedes breeding sites that the subsequent wet season sustains, as illustrated by 斯里兰卡迎来数年来最严重的登革热年，6月感染人数几近翻倍，累计超过44,000例. Control converges on three levers: environmental management to eliminate standing water, chemical vector control (larviciding and adulticiding), and the expanding Qdenga rollout. Brazil began Qdenga immunization through its national program in January 2024; Indonesia, Argentina, Thailand, and the United Kingdom approved the vaccine in the same window. Effective control requires sustained investment in urban sanitation and community surveillance, areas where funding gaps are widest in the highest-burden countries.

What to watch

• Whether the 2026 global dengue burden exceeds 2024's record, with Brazil and South Asia still reporting elevated case loads into the Northern Hemisphere summer
• Qdenga coverage in high-burden urban districts, particularly for school-age children in Indonesia, Bangladesh, and Vietnam
• Expansion of autochthonous transmission into Europe and the Eastern Mediterranean as Aedes albopictus spreads northward with warming temperatures
• Serotype circulation patterns: a DENV-3 resurgence carries elevated severe-disease risk in populations with prior DENV-1 or DENV-2 exposure, shaping fatality rates independently of case volume
• Sri Lanka's trajectory through its July-August monsoon peak, and whether the 2019 record of 105,000 cases is breached