Eurosurv. Expansion of influenza A(H1N1)pdm09 NA:S247N viruses with reduced susceptibility to oseltamivir, Catalonia, Spain, and in Europe, July to Oc

[tetano]

• Narcís Saubi[SUP]1,2[/SUP] , Cristina Andrés[SUP]1,2[/SUP] , Ignasi Prats-Méndez[SUP]1,2[/SUP] , Alejandra González-Sánchez[SUP]1,2[/SUP] , Alysa Davtyan[SUP]1[/SUP] , Rodrigo Vásquez-Mercado[SUP]1[/SUP] , Ariadna Rando[SUP]3[/SUP] , Patricia Nadal[SUP]3[/SUP] , Juliana Esperalba[SUP]3,4[/SUP] , Maria Arnedo[SUP]3[/SUP] , Marina Vicente[SUP]3[/SUP] , Eva Balada[SUP]3[/SUP] , Jacobo Mendioroz[SUP]5[/SUP] , María Carmen Martín[SUP]3[/SUP] , Karen García-Camuñas[SUP]3[/SUP] , Raquel Vaz[SUP]3[/SUP] , Adrià Najarro[SUP]3[/SUP] , Susana Bernalte[SUP]3[/SUP] , Nieves Larrosa[SUP]3,4[/SUP] , Andrés Antón[SUP]1,2,4[/SUP] , on behalf of the SIVIC Infectious diseases sentinel network[SUP]6[/SUP]

Between July and October 2025, among the total 117 influenza A(H1N1)pdm09 strains characterised in Catalonia, 20% to 100% per week were carrying the NA:S247N substitution. The mutation, conferring reduced susceptibility to oseltamivir, was phenotypically confirmed (IC50 between 0.82 and 1.63 nM, compared to median IC50 of 0.3 nM for susceptible strains). An increased proportion of S247N variants was also observed in sequence data (10,944 sequences) from other parts of Spain and five of 35 submitting countries across Europe.​
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https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2025.30.48.2500873