Record-breaking dengue epidemic in Brazil, 2024: nationwide analysis of 10.5 million cases and DENV-3 reemergence

Brazil experienced the largest dengue epidemic ever documented in any country in a single calendar year, with 10.5 million notified cases and 247,000 hospitalizations in 2024. Using publicly available national surveillance and hospital admission data, we characterize the epidemiological trajectory of this unprecedented outbreak. The effective reproduction number (Rt) peaked at 1.248 during epidemiological week 8, preceding the national case peak by approximately four weeks. Dengue virus serotype 3 (DENV-3) reemerged following a 16-year absence, exposing an estimated 50 million Brazilians born after 2008 without serotype-specific immunity. The 2024 epidemic exceeded the previous national record by 238%. These findings carry immediate implications for dengue vaccine rollout, vector control policy, and climate-adaptive public health planning.