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 07/2021, 31 of 29 953 non-sentinel specimens (from 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: 16 were type A and 15 were type B.


  • Since the beginning of the season, 665 of 393 149 non-sentinel specimens tested positive for influenza viruses; 335 (50.4%) were type A and 330 (49.6%) type B. Of 64 subtyped A viruses, 27 (42.2%) were A(H1N1)pdm09 and 37 (57.8%) were A(H3N2). Of 330 type B viruses, only 7 were ascribed to a lineage: 6 B/Victoria and 1 B/Yamagata.
Genetic characterization

Since week 40/2020, 11 viruses have been characterized genetically:


  • 5 type A: 4 influenza A(H3) with 2 attributed to the HA subgroup 3C.2a1b + T131K-A, represented by A/Slovenia/1637/2020, 1 attributed to the HA subgroup 3C.2a1b + T135K-A, represented by A/Denmark/3264/2019 and 1 attributed to the HA subgroup 3C.2a1b+T135K-B represented by A/Hong Kong/2671/2019); and 1 A(H1)pdm09 attributed to the group 6B.1A5A + 187V/A represented by A/Guangdong-Maonan/SWL1536/2019.


  • 6 type B: 2 B(Vic)-lineage clade 1A (d162-164) represented by B/Washington/02/2019 and 4 B(Vic) that were not assigned to any clade.


ECDC published the December virus characterisation report that describes the available data from viruses circulating recently including the season 2019-20. At that point, no antigenic data relating to viruses detected in the course of the 2020-2021 influenza season had been generated and the report was based on an analysis of seasonal influenza HA sequenced most recently and submitted to GISAID. This and previously published influenza virus characterization reports are available on the ECDC website.



Antiviral susceptibility of seasonal influenza viruses

Since the beginning of the season, 4 influenza viruses have been tested for susceptibility to neuraminidase inhibitors: two influenza A(H3) viruses and 2 influenza B/Victoria viruses for which sequence analysis indicated normal inhibition by both oseltamivir and zanamivir.