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ECDC reflects on influenza season 2011/12 in its annual “Influenza in Europe” surveillance report

15 Oct 2012
Influenza in Europe, Season 2011-2012
A year’s worth of surveillance data are summarised in the new Influenza in Europe, Season 2011–2012 surveillance report. It concludes that the influenza season 2011/12 started late and there was no particular pattern in its geographical progression. Its intensity was mild and unusually low in the majority of countries. Elderly and infants aged 0–4 years were the most severely affected groups of patients. With the return of A(H3N2) virus, a shift to older ages in severe influenza cases was observed.

The A(H1N1)pdm09 viruses continued to circulate, but they were largely exceeded by A(H3N2) and by B viruses, with the latter being especially important late in the season. Genetic characterisations of A(H3N2) viruses have shown important antigenic diversity resulting in an imperfect match with the vaccine strain. This was also reflected in the relatively low vaccine effectiveness observed and led to the WHO decision to recommend changing the seasonal influenza vaccine composition for the 2012–2013 season.

The influenza surveillance season in Europe lasts from beginning of October (week 40) of any given year to mid-May (week 20) of the following year, when ECDC provides weekly updates of influenza surveillance data. Between seasons, more limited information is gathered on the virological characteristics of circulating viruses, quantitative clinical data and severe acute respiratory infections. ECDC also maintains a year-round epidemic intelligence function to detect unusual events including those possibly related to influenza transmission.

The annual ECDC Influenza in Europe report is based on data and analyses covering all EU Member States, Iceland and Norway from week 40/2011 to week 20/2012 (not all participating countries contributed to each component of the surveillance system every week).

Resources on ECDC website:

Read  WHO Review of the 2011-2012 winter influenza season covering all northern hemisphere.

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