South America is experiencing the worst dengue season ever recorded. Brazil reported 5.9 million suspected dengue cases and over 5,900 deaths in 2024, shattering its previous annual record of 1.6 million cases set in 2015. PandemicAlarm rates the continental dengue situation at 3/5 severity. Not a global emergency, but a sustained crisis with no sign of slowing.
What's driving the surge?
El Nino conditions in 2023-2024 brought higher temperatures and heavier rainfall across much of South America, creating ideal breeding conditions for Aedes aegypti mosquitoes. Warmer winters meant mosquito populations never crashed the way they normally would during cooler months. Stagnant water from above-average rainfall multiplied breeding sites in urban areas.
Climate change is amplifying the effect. Average temperatures across Brazil's southeast — home to Sao Paulo, Rio de Janeiro, and Belo Horizonte — have risen by 1.1°C since 1990. That margin is enough to extend mosquito breeding seasons by several weeks and push Aedes populations into highland cities that historically saw little dengue.
Urban density compounds everything. Over 87% of Brazil's 214 million people live in cities. Dense neighborhoods with inconsistent waste collection, open water storage containers, and limited air conditioning give mosquitoes abundant habitat and constant access to human hosts.
How far has it spread beyond Brazil?
Argentina recorded over 583,000 dengue cases in 2024, its worst year on record. Buenos Aires, once considered too far south for significant dengue transmission, now reports thousands of locally acquired cases annually. Paraguay and Peru both reported record surges.
All four dengue serotypes (DENV-1 through DENV-4) are circulating simultaneously across the continent. That matters because infection with one serotype provides lifelong immunity to that serotype but can actually increase the risk of severe dengue upon infection with a different serotype, a phenomenon called ADE (antibody-dependent amplification). Simultaneous circulation of all four types raises the likelihood of secondary infections that turn severe.
Is the Qdenga vaccine helping?
Brazil became the first country to launch mass dengue vaccination in February 2024, using the Qdenga vaccine (TAK-003) manufactured by Takeda. The initial rollout targeted children aged 10 to 14 in high-burden municipalities. By mid-2025, over 5 million doses had been administered.
Early effectiveness data is encouraging. A real-world study from Parana state published in late 2025 showed 73% efficacy against symptomatic dengue and 89% against dengue hospitalization in the target age group. But 5 million doses in a country of 214 million is a fraction of what's needed. Supply constraints have limited the rollout. Qdenga is a two-dose vaccine given 3 months apart, and Takeda's manufacturing capacity cannot yet meet demand from Brazil alone, let alone the rest of Latin America.
What should you watch?
Southern hemisphere autumn begins in March, which should reduce mosquito activity as temperatures cool in Brazil's south and Argentina. But northern Brazil and equatorial regions see no meaningful seasonal reprieve. If 2026 follows a La Nina pattern, rainfall may decrease in some areas, potentially easing pressure. Or it may not. Climate variability makes seasonal predictions less reliable than they used to be.
For travelers to South America, dengue prevention means the same thing it always has: mosquito bite avoidance. Use repellents containing DEET or picaridin. Stay in accommodations with window screens or air conditioning. Wear long sleeves during peak biting hours, which for Aedes aegypti are early morning and late afternoon.
Track the dengue situation across South America on the PandemicAlarm map and read our full dengue explainer for more on how the virus works and why climate change is expanding its reach.