Fifteen Years of Dengue Activity Reveal a Hyperendemic Pattern in Ceará
Brazil’s dengue burden has long moved in large, cyclical surges, but Ceará State shows how relentless that transmission can become when all four serotypes circulate in the same population. From 2010 through January 2025, laboratory-confirmed dengue cases accumulated across nearly the entire country, and Ceará tracked those national waves with a consistently high local burden. In the state, dengue was eventually reported in all 184 municipalities, a geographic spread that leaves little room for complacency in routine surveillance or outbreak response.
The data place Ceará squarely in the center of Brazil’s dengue problem. Across the 15-year period, the state recorded 131,961 laboratory-confirmed cases, corresponding to a cumulative incidence of 1,500 cases per 100,000 inhabitants. Nationally, Brazil reported 1,657,046 laboratory-confirmed cases across 98.9% of municipalities, a reminder that this is not a localized problem but a continental-scale arboviral challenge shaped by mosquito ecology, urban density, and repeated exposure to antigenically distinct viruses.
National Waves, Local Peaks, and a Shifting Seasonal Clock
Investigators assembled national epidemiologic data from Brazil’s Ministry of Health and additional state-level data from Ceará’s Central Laboratory of Public Health, then paired those records with sequencing of residual quantitative reverse transcription PCR–positive samples collected from February 2024 through July 2025. The design matters because dengue control depends on two things at once: seeing the epidemic curve and understanding which viral lineages are driving it. Without that pairing, a surge in case counts can be described, but not interpreted.
Thirteen major epidemic waves appeared at the national level during the study window. Annual incidence ranged from 4.0 to 190.4 cases per 100,000 inhabitants, and the largest epidemic arrived in 2024. Test positivity also varied widely, from 18.2% to 57.1% over the 15 years, indicating how sharply dengue transmission can accelerate in some seasons and then fade into relative quiet before the next rebound.
Seasonal timing differed between Brazil as a whole and Ceará. National epidemics clustered mainly from February through June, peaking in March and April, while Ceará’s epidemics extended later, from March through August, with a typical peak in May. In practical terms, the state faces a longer high-risk window than the country overall, which affects mosquito-control campaigns, diagnostic readiness, and hospital preparation. The virus is not waiting for a convenient calendar.
Serotype Co-Circulation Creates the Conditions for Recurrent Epidemics
Dengue has four genetically and antigenically distinct serotypes, and immunity to one does not reliably protect against the others. That biology is central to Ceará’s trajectory. The state remains hyperendemic, with DENV-1 and DENV-2 predominating and DENV-3 recently reintroduced. In a region where prior infection is common, repeated circulation of different serotypes sustains transmission and shapes the risk profile for severe disease across age groups and communities.
This is where epidemiology and immunology meet bedside reality. A population that has already experienced one serotype can still be vulnerable to another, and the alternating dominance of lineages can seed renewed outbreaks even when clinicians and public health teams feel they have seen the pattern before. Persistent circulation also complicates vaccine evaluation, because vaccine performance must be judged against a backdrop of shifting serotypes, intense baseline exposure, and large swings in incidence from year to year.
Dengue remains especially consequential because no specific antiviral treatment exists. Clinical care still hinges on early recognition, fluid management, and vigilance for warning signs and progression to severe dengue. In a hyperendemic state, those tasks become more difficult when caseloads surge and the timing of transmission expands beyond the usual peak months.
Sequencing Adds a Genomic Layer to the Epidemic Record
The genomic work strengthened the epidemiologic picture. Residual serum samples from DENV-1 through DENV-3 infections collected in 2024 and 2025 were sequenced on the MiSeq platform, assigned through the DENV typing tool, and then reconstructed phylogenetically. That approach helps link observed case spikes to the lineages moving through the population rather than treating each epidemic wave as an indistinct numerical event.
Genomic surveillance is especially valuable in a state like Ceará, where all four serotypes have circulated and where reintroduction of DENV-3 changes the immunologic terrain. When a serotype returns after a period of lower activity, the population contains a mix of susceptible people and individuals with prior heterotypic exposure, conditions that can amplify spread and complicate severity patterns. The genomic signal, in other words, is not ornamental. It helps explain why one season follows another with such little warning.
Why This Matters for Vaccine Evaluation and Surveillance Planning
The study’s central value is baseline construction. Ceará now has a clearer historical frame for interpreting postlicensure dengue vaccine performance, especially as Brazil enters an era in which multiple licensed vaccines are available. Dengvaxia, Qdenga TAK-003, and Butantan-DV are now part of the broader dengue prevention discussion, but real-world evaluation depends on knowing what transmission looked like before and during vaccine rollout.
A baseline from 2010 to 2025 is useful because it captures multiple epidemic cycles rather than a single anomalous season. It also shows that Ceará’s incidence can exceed national patterns, with epidemic peaks that coincide with the country’s broader waves but often reach higher levels locally. For public health teams, that means routine national figures may understate the intensity of the threat in specific states.
The state’s female-to-male ratio of 1.6, along with higher incidence among female persons nationally and in Ceará, adds another layer that deserves attention in future work, even though this report does not resolve why the imbalance appears. Exposure patterns, care-seeking behavior, occupational contact, and household mosquito contact all remain plausible contributors, but the present data stop at association.
What this report does show is a transmission system that is stable in its instability: recurrent waves, prolonged seasonal activity, and viral diversity that keeps reinfecting the population’s immunologic memory. For Ceará, the challenge is not only counting cases. It is preparing for the next serotype shift before the curve turns again.