Virus Characteristics

Details of the distribution of viruses detected in sentinel-source specimens can be found in the Primary care data section.



Non-sentinel virological data

For week 47/2022, 3 551 of 57 670 specimens from non-sentinel sources (such as hospitals, schools, primary care facilities not involved in sentinel surveillance, or nursing homes and other institutions) tested positive for an influenza virus; 3 336 (94%) were type A and 215 (6%) were type B. Of 976 subtyped A viruses, 539 (55%) were A(H3) and 437 (45%) were A(H1)pdm09. Of 3 type B viruses ascribed to a lineage, all were B/Victoria.


For the season to date, more influenza type A (n=15 358, 92%) than type B (n=1 237, 8%) viruses have been detected. Of 5 028 subtyped A viruses, 3 277 (65%) were A(H3) and 1 751 (35%) were A(H1)pdm09. Of 181 influenza type B viruses ascribed to a lineage, all were B/Victoria (85% of type B viruses were reported without a lineage).


Genetic characterization

Of the 119 genetically characterized A(H1)pdm09 viruses up to week 47/2022, all belonged to clade 6B.1A.5a.2, of which 76 (64%) were represented by A/Norway/25089/2022, 42 (35%) were represented by A/Sydney/5/2021 and 1 (1%) was represented by A/Victoria/2570/2019.



Among the 125 A(H3) viruses characterized up to week 47/2022, all belonged to clade 3C.2a1b.2a.2, of which 58 (46%) were represented by A/Slovenia/8720/2022, 53 (42%) were represented by A/Bangladesh/4005/2020 and 11 (9%) were represented by A/Darwin/9/2021. Three viruses (3%) were not attributed to a subgroup.


Up to week 47/2022, 18 B/Victoria viruses were characterized and assigned to clade V1A.3a.2 of which 10 (56%) were represented by B/Austria/1359417/2021 and 8 (44%) were not attributed to a subgroup.


Currently, WHO’s October virus characterization report is available and describes available data from circulating viruses for the 2022-2023 influenza season: type A influenza virus circulation dominated over type B, due mainly to A(H3) viruses. Vaccination remains the best protective measure for prevention of influenza.


Previously published influenza virus characterization reports are available on the ECDC website (up to September 2022) and the WHO website.

Antiviral susceptibility of seasonal influenza viruses

Up to week 47/2022, 371 viruses were assessed for susceptibility to neuraminidase inhibitors (NAI) (118 A(H3), 118 A(H1)pdm09 and 17 B viruses genotypically and 109 A(H3), 6 A(H1)pdm09 and 3 B viruses phenotypically), and 135 viruses were assessed for susceptibility to baloxavir marboxil (BXM: 76 A(H3), 46 A(H1)pdm09 and 13 B viruses genotypically). Phenotypically no viruses exceeded IC50-fold-change thresholds for reduced susceptibility to NAI and, genotypically, no markers associated with reduced susceptibility to NAI or BXM were identified.




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