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 02/2022, 1 836 of 104 730 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; 1 800 (98%) were type A and 36 (2%) were type B. Of 774 subtyped A viruses, 20 (3%) were A(H1)pdm09 and 754 (97%) A(H3). No B viruses were ascribed to a lineage.


For the season to date, more influenza type A (n=27 825, 96%) than type B (n=1 168, 4%) viruses have been detected. Of 10 520 subtyped A viruses, 10 043 (96%) were A(H3) and 477 (4%) were A(H1)pdm09. Of 8 influenza type B viruses ascribed to a lineage, all were B/Victoria (99% of type B viruses were reported without a lineage).

Genetic characterization

Up to week 2/2022, 383 A(H3) viruses had been characterized genetically, 380 of which were attributed to clade 3C.2a1b.2a.2 and 3 to clade 3C.2a1b.1a. Fourteen A(H1)pdm09 viruses were characterized genetically and attributed to clade 6B.1A.5a.1. Up to week 2/2022, 3 B/Victoria viruses were characterized genetically, two belonging to clade V1A.3a.2 and one to clade V1A.3.


ECDC published the November virus characterization report: Currently type A influenza virus circulation is dominating over type B, due mainly to A(H3) viruses. Vaccination remains the best protective measure for prevention of influenza. However, based on post-infection ferret antisera data that the predominant H3N2 viruses in circulation are not well recognised by ferret antisera raised against viruses genetically and antigenically similar to the vaccine virus, indicating antigenic diversity, it is feasible that that the A(H3) vaccine component may induce less good recognition of the prevalent A(H3) viruses. Clinicians should therefore consider early antiviral treatment of at-risk groups with influenza infection, according to local guidance, to prevent severe outcomes.


This and previously published influenza virus characterization reports are available on the ECDC website.




* The table contains data from the case based INFLANTIVIR record type.

Antiviral susceptibility of seasonal influenza viruses

Up to week 02/2022, 421 viruses were assessed for susceptibility to neuraminidase inhibitors (268 A(H3) and 14 A(H1)pdm09 genotypically and 139 A(H3) phenotypically), and 238 viruses were assessed for susceptibility to baloxavir marboxil (225 A(H3) and 13 A(H1)pdm09 genotypically). No viruses with reduced susceptibility were identified.



* The administrative boundaries include spatial feature for Kosovo, this designation being without prejudice to position on status, and is in line with United Nations Security Council Resolution 1244 (1999) and the International Court of Justice Opinion on the Kosovo Declaration of Independence.