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Influenza A and B viruses represent significant global health threats, contributing substantially to morbidity and mortality rates. However, a comprehensive understanding of the molecular epidemiology of these viruses in Brazil, a continental-size country and a crucial hub for the entry, circulation, and dissemination of influenza viruses within South America, still needs to be improved. This study addresses this gap by consolidating data and samples across all Brazilian macroregions, as part of the Center for Viral Surveillance and Serological Assessment project, together with an extensive number of other Brazilian sequences provided by a public database during the epidemic seasons spanning 2021-23. Phylogenetic analysis of the hemagglutinin segment of influenza A/H1N1pdm09, A/H3N2, and influenza B/Victoria-lineage viruses revealed that in 2021 and in the first semester of 2022, the A/H3N2 2a.3 strain was the predominant circulating strain. Subsequently, the A/H3N2 2b became the prevalent strain until October, when it was substituted by A/H1N1pdm09 5a.2a and 5a.2a.1 lineages. This scenario was maintained during the year of 2023. B/Victoria emerged and circulated at low levels between December 2021 and September 2022 and then became coprevalent with A/H1N1pdm09 5a.2a and 5a.2a.1 lineages. The comparison between the vaccine strain A/Darwin/9/2021 and circulating viruses revealed shared mutations to aspartic acid at residues 186 and 225 across all A/H3N2 lineages from 2021 to 2023, altering the charge in the receptor-binding domain. For A/H1N1pdm09, the 2022 consensus of 5a.2a.1 and the vaccine strain A/Victoria/2570/2019 showed 14 amino acid substitutions. Key residues H180, D187, K219, R223, E224, and T133 are involved in hydrogen interactions with sialic acids, while N130, K142, and D222 may contribute to distance interactions based on docking analyses. Importantly, distinct influenza A lineage frequency patterns were observed across Brazil's macroregions, underscoring the regional variations in virus circulation. This study characterizes influenza A and B viruses circulating in Brazil, providing insights into their circulation patterns and dynamics across Brazilian macroregions. These findings hold significant implications for public health interventions, informing strategies to mitigate transmission risks, optimize vaccination efforts, and enhance outbreak control measures., Competing Interests: None declared., (© The Author(s) 2025. Published by Oxford University Press.)

The high numbers of COVID-19 cases and deaths in Brazil have made Latin America an epicentre of the pandemic. SARS-CoV-2 established sustained transmission in Brazil early in the pandemic, but important gaps remain in our understanding of virus transmission dynamics at a national scale. We use 17,135 near-complete genomes sampled from 27 Brazilian states and bordering country Paraguay. From March to November 2020, we detected co-circulation of multiple viral lineages that were linked to multiple importations (predominantly from Europe). After November 2020, we detected large, local transmission clusters within the country. In the absence of effective restriction measures, the epidemic progressed, and in January 2021 there was emergence and onward spread, both within and abroad, of variants of concern and variants under monitoring, including Gamma (P.1) and Zeta (P.2). We also characterized a genomic overview of the epidemic in Paraguay and detected evidence of importation of SARS-CoV-2 ancestor lineages and variants of concern from Brazil. Our findings show that genomic surveillance in Brazil enabled assessment of the real-time spread of emerging SARS-CoV-2 variants., (© 2022. The Author(s).)

The appearance of new variants of SARS-CoV-2 has recently challenged public health authorities with respect to tracking transmission and mitigating the impact in the evolving pandemic across countries. B.1.525 is considered a variant under investigation since it carries specific genetic signatures present in P.1, B.1.1.7, and B.1.351. Here we report genomic evidence of the first likely imported case of the SARS-CoV-2 B.1.525 variant, isolated in a traveler returning from Nigeria., (© 2021 Wiley Periodicals LLC.)