Weekly influenza update, week 46, November 2017

Summary

• Influenza activity across Europe remained at a low level.
• Of the individuals sampled on presenting with ILI or ARI to sentinel primary healthcare sites, 3.7% tested positive for influenza viruses, which is similar to the previous week (4.4%).
• Data from 21 countries or regions reporting to the EuroMOMO project indicated that all-cause excess mortality was within normal ranges for this time of year.

2017/18 season overview 

• Since week 40/2017, few influenza viruses have been detected in sentinel and non-sentinel specimens.
• For detections from sentinel surveillance systems, the proportions of influenza A(H1N1) pdm09 and A(H3N2) viruses were similar, while from non-sentinel sources most detections were A(H3N2). For both sentinel and non-sentinel surveillance systems, most influenza B viruses assigned to a lineage were B/Yamagata.
• While low in number (n=34), over 68% of the A(H3N2) viruses genetically characterized belonged to clade 3C.2a, the vaccine virus clade, as described in the WHO recommendations for vaccine composition for the northern hemisphere 2017–18.