Portuguese Laboratory Network for the Diagnosis of Influenza and Respiratory VirusesGuiomar, RaquelHenriques, Camilada Silva, Susana PereiraGomes, LicíniaDias, DanielaVerdasca, NunoNunes, BaltazarRodrigues, Ana PaulaGuimarães, João TiagoCardoso, Maria JoãoRamos, AngelicaPereira, PauloCastro, Ana PaulaMarques, Maria HelenaMota, PaulaFerreira, AnaLopes, PauloAbreu, GabrielaPedrosa, AdrianaSilva, Ana CristinaVarzim, Póvoa deMartins, Nádia SousaMesquita, AurélioMajar, MarinaCalheiros, Ana FilipaMota Freitas, José AntónioVieira, Sandra MargaridaGomes, SusanaMagalhães, CacildaSoares, Maria J.Montanha, Maria JoséSilva, HelenaFerreira, CarlaReis, TeresaCosta, TiagoMarques, BrunoRodrigues, RicardoCunha, MarioSeabra, SofiaPires, AnaNunes, DianaToscano, CristinaSilva, LuísLuís, JoãoMira, AnaSerrano, AnaMoreira, InêsLoureiro, AnaMarques, AnaAlves, José2026-05-142026-05-142026-02-121025-496XPURE: 162944010PURE UUID: ec63e98d-f89f-4f15-84ba-ffcfc5c96730Scopus: 105030219107PubMed: 41684322PubMedCentral: PMC12905529WOS: 001699048500001http://hdl.handle.net/10362/203096Publisher Copyright: © 2026, European Centre for Disease Prevention and Control (ECDC). All rights reserved.The 2025/26 season was marked by co-circulation of influenza A subtypes, with the first detection of A(H3N2) subclade K in September 2025. In August 2025 in Portugal, 14.8% (95% CI: 12.2–17.8) of 886 persons tested had cross-protective antibodies against this subclade. The overall seroprevalence against circulating A(H1N1) pdm09 strains was 28.1% (95% CI: 24.4–32.0). These data highlight the presence of previous cross-reactive antibodies and the possible advantage of vaccination in the extent of detectable antibodies against influenza viruses.437567engEpidemiologyMicrobiologyImmunology and Microbiology (miscellaneous)Public Health, Environmental and Occupational HealthMicrobiology (medical)VirologyInfectious DiseasesSDG 3 - Good Health and Well-beingjournal article10.2807/1560-7917.ES.2026.31.6.2600070https://www.scopus.com/pages/publications/105030219107