Weekly influenza update, week 3, January 2018
Influenza activity was widespread in the majority of reporting countries, while increasing activity was observed in eastern European countries. Both influenza types B and A viruses were co-circulating with a higher proportion of type B viruses. Different patterns of type and A subtype circulation were observed between countries in the Region. Of the individuals sampled, on presenting with ILI or ARI to sentinel primary healthcare sites, 52% tested positive for influenza viruses, a slight increase compared to recent weeks (42–50%).
2017/18 season overview
- For the Region overall, a higher proportion of type B viruses compared to type A viruses has been detected in sentinel sources, whereas in non-sentinel sources the proportions are roughly similar. Of the type A detections from sentinel sources, A(H1N1)pdm09 viruses have outnumbered A(H3N2) viruses, while in non-sentinel sources more A(H3N2) viruses were reported than A(H1N1)pdm09 viruses.
- For type B viruses from both sentinel and non-sentinel sources, B/Yamagata lineage viruses have greatly outnumbered those of the B/Victoria lineage. B/Yamagata lineage is not included in the trivalent seasonal influenza vaccine.
- Different patterns of dominant type and A subtype were observed across the countries in the Region, which may be due to the relative weights of information being derived from sentinel, non-sentinel and severe influenza sources of information.
- While low in number, 64% of the genetically characterized A(H3N2) viruses belonged to clade 3C.2a, the clade of the vaccine virus described in the WHO recommendations for vaccine composition for the northern hemisphere 2017–18, and 36% to clade 3C.2a1, with viruses in both clades being antigenically similar.
- A situation analysis that describes the early season evolving epidemiological pattern was published by WHO Regional Office for Europe in January.
- An early risk assessment based on data from EU/EEA countries was published by ECDC on 20 December 2017.
- Vaccine effectiveness estimates from Stockholm country report 31% (95%CI: 14–45) among the patients 65 years or older. Sweden reports a mainly B virus circulation so far.
- Based on data submitted to the EuroMOMO project there has, over the past weeks, been increased all-cause mortality among the elderly, notably in some countries in the south of the European Region and the United Kingdom (Scotland).
- Additional information on global influenza activity is available from WHO’s biweekly global updates.
See all weekly influenza updates
Seasonal influenza is a preventable infectious disease with mostly respiratory symptoms. It is caused by influenza virus and is easily transmitted, predominantly via the droplet and contact routes and by indirect spread from respiratory secretions on hands etc.Read more
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