The role of climate and immunity in Brazil unprecedented outbreak of dengue in 2024

In Brazil’s 2024 dengue epidemic, nine of 27 states—mostly in the Southeast—hit their highest incidence in 25 years, contributing 97% of cases with only 67% of the population.

• Why it matters: The outbreak’s scale (almost 5.7 million cases in 2024 vs under 1.3 million in 2023) raised uncertainty about whether climate, immunity, or reporting shifts best explain where transmission intensified.
• What they did: The study compared state-level 2024 incidence against 2000–2023 and quantified anomalies, then used generalized additive models on effective reproductive numbers and a mechanistic SEIR-SEI framework to estimate susceptibility.
• The result: Transmission stayed substantial even at the highest temperatures, while reproductive numbers declined with lagged cumulative incidence, and 2024 outbreaks were predicted only when both temperature and susceptibility were included.

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