Emergence and spread of NA-I223V and NA-S247N double-mutant A(H1N1)pdm09 influenza viruses with reduced oseltamivir susceptibility in the Netherlands and beyond, 2023 to 2026
Eurosurveillance
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September 23 2026
Abstract:
"In 2023/24, A(H1N1)pdm09 influenza viruses with neuraminidase (NA)-S247N emerged in NA-clade C.5.3.3 carrying NA-I223V, spread internationally, then faded. Such double mutants reappeared sporadically in 2024/25. They expanded again in 2025/26 in NA-clade D.3 viruses carrying NA-S247N after acquiring NA-I223V in Europe – notably Spain, the Netherlands, Finland and France, and beyond. Dutch double mutants from both seasons showed median 12- and 13-fold reduced inhibition by oseltamivir. These findings underscore the need for ongoing genomic and phenotypic monitoring of antiviral susceptibility."
Felix Garza, Z., Eggink, D., Bagheri, M., van den Brink, S., Goderski, G., Pronk, M., Lexmond, P., Hooiveld, M., van Gageldonk-Lafeber, R., Koel, B., Fouchier, R. and Meijer, A. (2026). Emergence and spread of NA-I223V and NA-S247N double-mutant A(H1N1)pdm09 influenza viruses with reduced oseltamivir susceptibility in the Netherlands and beyond, 2023 to 2026. Eurosurveillance, 31(36). doi:10.2807/1560-7917.es.2026.31.36.2600733.
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