Risk assessment: Seasonal influenza 2011–2012 in Europe (EU/EEA countries)

Risk assessment

ECDC produces an annual risk assessment for the seasonal influenza epidemics in Europe. This is following both a recommendation in the report on the handling of the 2009 pandemic adopted by the World Health Assembly in May 2011 and the model developed by ECDC during that pandemic. The first EU seasonal influenza risk assessment was published in January 2011, following the start of the influenza season in late November 2010. In 2012, the season started later than in most years, with the first five countries exceeding their epidemic threshold in week 3/2012.

Executive summary

On 12 March 2012 ECDC published its annual risk assessment on seasonal influenza 2011/2012 in Europe. ECDC points out that on this occasion the seasonal influenza epidemics in Europe started unusually late and unlike the last few winters have not followed any particular geographical progression.

The annual EU season influenza risk assessment follows a structure that was established in the 2009 pandemic and gives an early description of the epidemics of seasonal influenza in the EU/EEA countries drawing on the experience of the first affected countries. The assessment identifies the special features of the current season, especially areas where public health or clinical actions are justified. It also highlights areas of uncertainty and therefore priorities for further work. The first ECDC seasonal influenza risk assessment was published in January 2011.

Virological surveillance data for the season shows that the epidemics have so far been dominated by the A(H3N2) viruses, but recently the proportion of B viruses has increased. The data also shows that some A(H1N1)pdm09 viruses are also circulating, although these are far lower in numbers than in the previous two seasons. However, they are over-represented among the people most severely affected that have been hospitalised with a confirmed infection. Antiviral resistance to the neuramindase inhibitors is almost non-existent this season.

At this stage, the role that B viruses will play towards the end of the season is uncertain. Other areas of uncertainty are the degree of effectiveness of the seasonal influenza vaccine in a season when there is an imperfect match between the vaccine and the circulating A(H3N2) viruses and the level of premature mortality that can be expected in older people due to the dominance of the virus A(H3N2). It will be difficult to tease apart the effects due to the influenza from those consequences of the cold weather.

ECDC annual seasonal influenza risk assessments