Conclusions and next steps

In a few countries in the European Region, the clinical incidence of influenza increased during the summer and as a result of pandemic influenza activity. The vast majority of influenza detections were pandemic (H1N1) 2009, as was the case globally. In the European Region, however, fewer seasonal A (H3) viruses were detected (2.3% of A-subtyped influenza viruses) compared to global estimates provided mainly from countries in the southern hemisphere (8.8% of A-subtyped influenza viruses). This may reflect the fact that pandemic infections occurred in Europe outside the normal influenza season, when seasonal influenza viruses are not normally circulating at detectable levels.

WHO European Member States’ uninterrupted monitoring during the first months of the pandemic provided valuable information on the situation, and demonstrated the robustness of influenza surveillance in the Region. It is essential that countries maintain surveillance to track geographic spread during the current influenza season, to monitor the relative proportions of seasonal, pandemic and other respiratory viruses in circulation and to detect the presence of any antigenically drifted pandemic (H1N1) 2009 or seasonal influenza viruses. In particular, the antigenicity of A (H3N2) should be monitored, since a new strain (A/Perth/16/2009 (H3N2)) has emerged. This strain has been included in the vaccine for 2010 southern hemisphere winter season influenza, but not in the WHO vaccine composition recommendations for the 2009/2010 northern hemisphere season. Antiviral susceptibility profiles of pandemic and seasonal influenza viruses, particularly for oseltamivir and zanamavir, also need to be monitored in cases when treatment fails, in people who develop symptoms while receiving antiviral prophylaxis, in severe and fatal cases and in a selection of mild cases as part of routine monitoring.

Member States should continue monitoring for changes in the epidemiological and clinical characteristics of severe cases, which may also indicate a change in the virulence of circulating viruses. Nationwide testing and reporting of severe cases should be considered to monitor for subpopulations at greater risk of severe outcomes. This surveillance should incorporate the continuing and timely monitoring of hospital and ICU surge capacity as well. WHO/Europe outlines strategies to implement integrated sentinel influenza surveillance in WHO European guidance for influenza surveillance in humans.

Governments will need to ensure that their national pandemic preparedness plans are flexible enough to enable them to take action that is evidence based, commensurate to the risk and adapted to the resources available. While the 2009/2010 influenza season is certainly exceptional, the job of sentinel surveillance and routine monitoring is not only largely unchanged but also more critical than ever to provide the evidence to inform sound policy decisions.