Genomic and Epidemiological Characterization of DENV-1 and DENV-2 Co-Circulation During the 2023-2024 Dengue Epidemic in Espírito Santo, Brazil.

In 2023 and 2024, Espírito Santo state, Brazil, experienced its largest dengue epidemic in 30 years, with record numbers of cases and deaths. This study aimed to characterize confirmed dengue cases and the dengue virus (DENV) during the epidemic and pre-epidemic periods. A population-based descriptive study integrated with cross-sectional genomic sampling was conducted using data from the eSUS Health Surveillance System (2020-2024) and molecular analysis of serum samples (2023-2024). Whole 26 DENV genomes were obtained and combined with public data for phylogenetic reconstruction. In 2023, 127 070 dengue cases were reported; 2.8% showed warning signs or severe dengue, 2.6% required hospitalization, and 99 cases resulted in death. In 2024, 131 170 cases were reported, with 2.0% showing warning signs or severe dengue, 2.3% requiring hospitalization, and 42 fatalities. Four lineages were detected: DENV-1 genotype V lineages 1V_A and 1V_E.1, DENV-2 genotype II lineage 2II_F.1.1.2, and genotype III lineage 2III_C.1.1. These lineages were closely related to viruses from other regions in Brazil and South America. Our findings highlight the complex dynamics of DENV in Espírito Santo state and hypothesize that the multiple introduced DENV lineages and genetic diversity may have contributed to the magnitude and sustained transmission observed over consecutive years.