Virus characteristics

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

Viruses detected in non-sentinel source specimens 

For week 1/2019, 4 896 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; 4 851 (99.1%) were type A and 45 (0.9%) type B. Of 1 068 subtyped A viruses, 70.7% were A(H1N1)pdm09 and 29.3% were A(H3N2).

For the season so far, a substantially greater number of influenza type A (n=15 690, 97.6%) than type B viruses (n=386, 2.4%) has been detected. Of 4 779 subtyped A viruses, 68.8% were A(H1N1)pdm09 and 31.2% A(H3N2). Of 13 influenza type B viruses ascribed to a lineage, 6 were B/Yamagata and 7 were B/Victoria; 373 type B viruses were reported without a lineage (Table).

Genetic characterization

Since week 40/2018, genetic characterizations of 215 viruses have been reported: 151 were A(H1)pdm09 viruses belonging to the A/Michigan/45/2015 (6B.1) clade; 62 were A(H3) viruses, with 44 belonging to the A/Alsace/1746/2018 (3C.2a1b) subgroup, 3 to the A/Switzerland/8060/2017 (3C.2a2) subgroup, 4 to the A/Cote d'Ivoire/544/2016 (3C.2a3) subgroup, 8 to the A/England/538/2018 (3C.3a) clade and 3 attributed to a subgroup not listed. 1 B/Yamagata lineage virus was characterized as belonging to the B/Phuket/3073/2013 clade (clade 3) and 1 B/Victoria lineage virus was characterized as belonging to the B/Brisbane/60/2008 clade (clade 1A). 

Only 14 A(H3N2) viruses have been antigenically characterized, but recent A(H3N2) viruses were shown to be antigenically similar to the reference virus A/Singapore/INFIMH-16-0019/2016 that is the vaccine virus component included in the northern hemisphere vaccine for 2018-2019 (more information can be found here).

The latest characterization data are summarized in the ECDC summary report for November.

For more information on virus characterizations for EU/EEA countries, see earlier WHO CC London Influenza virus characterisation reports.

The recommended composition of the trivalent influenza vaccine for the northern hemisphere 2018–2019 season included an A/Michigan/45/2015 (H1N1)pdm09-like virus, an A/Singapore/INFIMH-16-0019/2016 (H3N2)-like virus and a B/Colorado/06/2017-like virus (B/Victoria lineage). For quadrivalent vaccines, a B/Phuket/3073/2013-like virus (B/Yamagata lineage) was recommended. The full report can be found here. A comment by ECDC can be seen here.

On 27 September 2018, WHO announced the recommended vaccine composition for the southern hemisphere 2019 season. The recommendations matched the A(H1N1)pdm09 and B components for the 2018–2019 northern hemisphere season, but the A(H3N2) component was changed for egg-based vaccines. The full report can be found here.

Antiviral susceptibility testing

131 A(H1N1)pdm09, 27 A(H3N2), and 2 type B viruses with collection dates in weeks 40/2018–1/2019 have been tested for susceptibility to neuraminidase inhibitors. 1 A(H1N1)pdm09 and 1 B virus showed evidence of reduced inhibition by neuraminidase inhibitors.