Phylogeographic Dynamics and Spatial Connectivity of Influenza A(H3N2) in Brazil

Le résumé fourni par la source

Influenza A(H3N2) viruses show continuous antigenic and genetic evolution, requiring sustained molecular surveillance to understand their circulation and geographic spread. This study investigated the epidemiological, evolutionary, and phylogeographic dynamics of A(H3N2) viruses circulating in Brazil between 2011 and 2019. Epidemiological surveillance data from Northern and Northeastern Brazil were analyzed together with hemagglutinin (HA) gene sequences generated in this study and sequences retrieved from GISAID EpiFlu database. Phylogenetic and Bayesian phylogeographic analyses were performed to characterize genetic diversity and viral dispersal. Among 23,278 respiratory samples, 1,003 (4.31%) were positive for A(H3N2), with seasonal peaks occurring mainly between epidemiological weeks 13 and 16. Phylogenetic analyses revealed successive lineage replacement, with predominance of 3C.2a-derived clades after 2015. Phylogeographic reconstruction identified multiple international introductions into Brazil and extensive viral movement among Brazilian regions, with Southeastern Brazil acting as the main hub of national connectivity. Northern and Northeastern Brazil participated predominantly as recipient regions while also contributing to onward viral dissemination. These findings highlight the interconnected nature of A(H3N2) circulation in Brazil and reinforce the importance of integrating genomic and epidemiological surveillance to understand influenza dynamics.

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