{Summary}
Surveillance and monitoring | 6 November 2026
This report summarises influenza virological surveillance data from all 30 European Union and European Economic Area (EU/EEA) countries from week 40 2025 to week 33 2026, as reported by National Reference Laboratories (NRLs) to The European Surveillance System (TESSy) at the European Centre for Disease Prevention and Control.
Executive summary
Detections
Within the reporting period, 256 967 influenza virus detections (sentinel and non-sentinel combined) were reported, of which 249 514 (97.1 %) were type A and 3 292 (1.3 %) were type B viruses; another 4 161 viruses were reported untyped.
Of the 56 946 subtyped influenza A viruses (23 % of type A viruses), 20 072 (35 %) were A(H1)pdm09 and 36 874 (65 %) were A(H3).
Of the 3 292 reported influenza type B viruses, the lineage for 372 (11 %) was determined as all falling into the B/Victoria/2/87-lineage (B/Victoria).
A(H1N1)pdm09
For A(H1N1)pdm09 viruses, 25 countries reported 6 636 haemagglutinin (HA) sequences.
Of all A(H1N1)pdm09 viruses, the majority belonged to clade 5a.2a.1, newly emerged subclade D.3.1.1 (6 270, 95 %), defined by HA substitutions R113K, A139D, E283K and K302E and which was not represented by any reporting category or reference strain defined for this season.
Within the genetic diversification of 5a.2a.1 clade, 340 (5 %) viruses belonged to subclade D.3.1, carrying HA substitutions T216A, T120A, I372V, I460T, V520A and was represented by A/Missouri/11/2025 egg- and cell-based vaccine strains for northern hemisphere 2026-2027 influenza season.
Among the 838 antigenically characterised A(H1)pdm09 viruses, the main reported categories were A/Missouri/11/2025-like, clade 5a.2a.1(D.3.1) and A/Victoria/4897/2022-like, clade 5a.2a.1(D), representing 44.2 % and 51.1 %, respectively.
In total, 6 612 A(H1N1)pdm09 viruses were assessed for antiviral susceptibility to oseltamivir and/or zanamivir and/or baloxavir marboxil by 25 countries.
Phenotypically assessed reduced and highly reduced inhibition by Oseltamivir was observed for ten (2.3 %) and three (0.7 %) of the 437 tested A(H1N1)pdm09 viruses.
Genetic substitutions associated with reduced and highly reduced inhibition by Oseltamivir were observed for 147 (2.4 %, associated with neuraminidase (NA) gene substitutions I223V and S247N mainly, or NA_I223M/T or NA_S247R) and 15 (0.2 %, associated with NA_H275Y or NA_N295S) of the 6 088 assessed viruses, respectively.
For Zanamivir, substitutions associated with reduced and highly reduced inhibition were observed for one (<0.1 %, associated with NA_S247R) and one (<0.1%, associated with NA_Q136K) of the 6 089 assessed viruses, respectively.
Out of the 4 020 assessed A(H1N1)pdm09 viruses for baloxavir marboxil, substitutions associated with reduced susceptibility were observed for four (0.1 %, associated with polymerase acidic (PA) protein gene substitutions E23G or PA_A37T or PA_E199G/K) viruses.
A(H3N2)
For A(H3N2) viruses, 25 countries reported 9 538 HA sequences.
All A(H3) HA sequences fell into clade 2a.3a.1 and there to seven different subclades.
Most viruses (8 808, 92%) fell into newly emerged subclade K (former J.2.4.1) characterised by K2N, S144N (a potential addition of an N-glycosylation site), N158D, I160K, Q173R, T328A and S378N and represented by A/Norway/8765/2025.
The remaining 719 A(H3N2) viruses belonged to subclades J.2 (83, 0.9%; which is the NH 2025-26 season vaccine strain represented by A/Croatia/10136RV/2023), J.2.2 (47, 0.5%), J.2.3 (235, 2.5%), J.2.4 (47, 0.5%) and J.2.4.2 (307, 3.2%).
Among the 1 137 antigenically characterised A(H3) viruses, the main reported categories were A/Croatia/10136RV/2023-like, subclade J.2, A/Singapore/GP20238/2024-like, subclade J.2.4 and A/Norway/8765/2025-like, subclade K, representing 43.3 %, 34.7 % and 10.6 %, respectively.
In total, 9 441 A(H3N2) viruses were assessed for antiviral susceptibility to oseltamivir and/or zanamivir and/or baloxavir marboxil by 25 countries.
Phenotypically assessed reduced inhibition to Oseltamivir was observed for one (0.2%) of the 505 tested A(H3N2), and reduced inhibition to Zanamivir was observed for one (0.2%) of 491 tested A(H3N2) viruses.
Genetic substitutions associated with reduced and highly reduced inhibition by Oseltamivir were observed for 19 (0.2%, associated with NA_S331R mainly or NA_K249E or NA_N329R) and three (<0.1%, associated with NA_E119V or NA_del245-248/247-250), respectively, of the 8 869 viruses that could be assessed.
Reduced inhibition by Zanamivir was observed for 17 (0.2%, associated with NA_S331R mainly or NA_del245-248/247-250) among the 8 883 viruses that could be assessed.
Out of the 5 397 assessed A(H3N2) viruses, substitutions associated with reduced susceptibility for baloxavir marboxil were observed for seven (0.1%, associated with PA_I38L) A(H3N2) viruses.
B/Victoria
For B/Victoria viruses, 14 countries reported 318 HA sequences.
The majority (288, 91%) of the viruses fell in the branch of subclade C.5 defined by D197E, compared with NH 2025-26 vaccine virus B/Austria/1359417/2021_Egg.
In that clade, the B/Victoria viruses fell into subclades C.5.6 (126, 40%), C.5.6.1 (89, 28%), C.5.1 (54, 17%) and C.5.7 (18, 6%).
Twenty-eight (9%) viruses represented the subclade C.3, where half of them belonged to subclade C.3.1 and half to C.3.3.
The 21 antigenically characterised B/Victoria viruses were all reported as B/Austria/1359417/2021-like, subclade C.
None of the 298 genotypically and 14 phenotypically tested B/Victoria viruses showed reduced susceptibility to neuraminidase inhibitors or baloxavir marboxil (when 250 viruses were tested for baloxavir).
Source: European Centre for Disease Control and Prevention, https://www.ecdc.europa.eu/en/publications-data/influenza-virus-characteristics-week-40-2025-week-33-2026-eueea
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