Rapid risk assessment: circulation of drifted influenza A(H3N2) viruses in the EU/EEA, 22 December 2014

risk assessment
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European Centre for Disease Prevention and Control. Circulation of drifted influenza A(H3N2) viruses in the EU/EEA – 22 December 2014. Stockholm: ECDC; 2014.

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Surveillance data gathered since 1 October 2014 indicate that in the first ten weeks of the 2014–15 influenza season, viruses in EU/EEA countries have been predominantly A(H3N2) rather than A(H1N1)pdm09 and type B viruses.

Executive summary

In previous seasons, influenza A(H3N2) viruses were associated with more severe disease than A(H1N1) and type B viruses; they were also associated with several outbreaks in long-term care facilities.
 
These observations indicate that the 2014-15 influenza season may be associated with a greater number of cases with more severe disease, given the higher proportion of A(H3N2) strains among isolates typed to date and the early evidence of drift that is likely to be associated with reduced vaccine effectiveness.
 
Influenza vaccine coverage among the elderly and the risk groups in most parts of Europe is low. However, the benefits of vaccination are considerable in protecting these population groups, even if vaccine effectiveness against one of the circulating viruses may turn out to be low.