Ceará’s Dengue Pattern Turned Hyperendemic Into a Moving Target
Ceará State has become one of Brazil’s most intensively monitored dengue settings, and the 2010–2025 record shows why. Over 15 years, dengue virus circulation did not simply persist; it shifted, layered, and re-entered the state through multiple lineages across all four serotypes. The result is a dense epidemiologic environment in which nearly every municipality has faced transmission, and where the arrival or return of a serotype can quickly alter population risk.
Brazil recorded 1,657,046 laboratory-confirmed dengue cases from January 3, 2010, to January 25, 2025, spanning 98.9% of municipalities across all 26 states and the Federal District. Ceará accounted for 131,961 laboratory-confirmed cases, with a cumulative incidence of 1,500 cases per 100,000 inhabitants. In a region already accustomed to endemic dengue, those numbers describe more than routine circulation. They reflect repeated epidemic waves moving through a population exposed to changing serotype pressure and repeated opportunities for secondary infection.
One detail stands out sharply: Ceará’s epidemic peaks usually came later and lasted longer than the national average. National outbreaks tended to peak in March and April, while Ceará’s epidemics typically peaked in May and extended from March through August. Persistent heat and humidity likely support a longer mosquito season, allowing Aedes populations to remain active for more months of the year and sustaining transmission after outbreaks elsewhere begin to wane.
Serotype Replacement Repeated Across the State
The serotype record in Ceará reads like a sequence of turnovers rather than a static background pattern. DENV-1 dominated from 2014 through 2019 and again from 2023 through 2025. DENV-2 reemerged in 2019, then nearly displaced the other serotypes in 2021 and 2022. Fortaleza, the state capital and largest city, documented co-circulation of DENV-1, DENV-3, and DENV-4 in 2015, a reminder that multiple serotypes can occupy the same urban setting at once.
By 2026, dengue had been reported in all 184 municipalities in Ceará, with cumulative incidence ranging from 41.4 to 8,566 cases per 100,000 inhabitants. Such spread leaves little room for complacency in surveillance. A municipality that has seen one dominant serotype one year may face a very different immunologic and virologic situation the next, especially when lineage replacement occurs after years of uneven exposure.
Sex- and age-stratified analysis added another layer. Female-to-male ratio reached 1.6, and incidence was higher among females nationally and in Ceará. Incidence was also higher in people 10–39 years of age than in those 70 years of age. The article does not resolve the social or behavioral reasons for those differences, but they matter operationally because dengue control depends on identifying where health-seeking behavior, exposure, and testing intersect with transmission.
Genomic Data Showed Repeated Introductions, Not a Single Local Line
Genomic sequencing brought the clearest evidence that Ceará’s epidemic pattern was being refreshed by outside introductions. Investigators sequenced 243 DENV genomes from cases reported between February 2024 and July 2025 across 45 municipalities. Complete or partial genomes were recovered for 218 samples, and 180 genomes with more than 70% coverage were classified into six lineages spanning DENV-1, DENV-2, and DENV-3.
The current epidemic, spanning 2024–2025, was driven mainly by DENV-1 lineage V_E1, which accounted for 61.6% of sequenced cases. DENV-2 lineage II_F1.1.2 predominated among DENV-2 detections and clustered with genomes from southeast and northeast Brazil and the United States. Another DENV-2 lineage, II_F1.1.5, grouped with sequences from France and the Dominican Republic, pointing to a recent international introduction. Those phylogenetic patterns matter because they show how quickly dengue can move through domestic travel corridors and, in some instances, across borders.
A single sentence captures the public health significance: DENV-3 returned after a long absence. The state had no local DENV-3 detections since 2015, yet DENV-3 genomes were found again in 2025 and belonged to lineage III_B3.2. They formed a well-supported clade with sequences from São Paulo and Florida and sat within a lineage widely circulating across the Americas. In practical terms, a serotype that has been absent for years can return to a population with limited contemporary immunity, increasing the risk of more intense transmission and more severe disease in people with prior heterologous exposure.
Why DENV-3 Matters for Future Severe Disease Risk
Dengue severity is shaped not only by the infecting serotype but also by infection history. In settings where DENV-1 and DENV-2 have co-circulated for years, the reintroduction of DENV-3 creates fresh conditions for sequential infection. Immunologic priming from a prior serotype can contribute to antibody-dependent enhancement, a biologically plausible pathway for more severe outcomes when a later infection is caused by a different serotype.
Ceará’s long period of co-circulation, combined with the new appearance of DENV-3, therefore has direct implications for hospitals, laboratories, and vaccination planning. The state is not facing a single wave from a stable viral background. It is facing a shifting antigenic environment in which population immunity may not match the next circulating serotype.
The study’s epidemiologic and genomic findings also provide a baseline for postlicensure vaccine evaluation. Brazil now has licensed dengue vaccines, including Dengvaxia, Qdenga TAK-003, and Butantan-DV. In a hyperendemic state like Ceará, vaccine performance will need to be interpreted against an evolving serotype mix rather than a fixed transmission pattern. If DENV-1 and DENV-2 remain dominant but DENV-3 continues to circulate, protection estimates may differ across time, geography, and prior exposure history.
Surveillance Gaps Could Mask the True Burden
The limitations are straightforward and important. Case counts depended on healthcare-seeking behavior, so asymptomatic infections and people who never presented for testing were not captured. The epidemiologic data could not distinguish primary from secondary infections. Some IgM-based diagnoses may have reflected cross-reactivity with Zika virus, which emerged in Brazil in 2015. Genomic data were limited to 2024–2025, and sparse historical sequences from Ceará prevented a fuller reconstruction of how these lineages moved through the state earlier in the decade.
Those constraints do not weaken the main message. They sharpen it.
Ceará has a sustained dengue transmission system in which all 4 serotypes have circulated, peak activity often extends later into the year than in Brazil overall, and recent genomes show both domestic and international lineage movement. The return of DENV-3 after a decade of absence deserves special attention because it may alter the clinical mix of future cases as prior immunity interacts with a newly reintroduced serotype. Continued serotype-specific surveillance remains essential for judging vaccine impact and for tracking the next shift in a transmission pattern that is clearly still in motion.