Schweiger B (2001): Nationale und globale Influenzasurveillance als Basis der jährlichen Impfstoffempfehlung. [Vaccine Recommendations are Based on National and Global Influenza Surveillance]
Bundesgesundheitsbl 44 (12): 1153-1161.

Influenza is still one of the most important infectious diseases. In Germany, excess mortality rates of more than 10,000 deaths were reported during a season with high influenza activity (e.g. 1998/99). Treatment of influenza infections was greatly improved by the availability of neuraminidase inhibitors. Nevertheless, vaccination will remain the most important option for controlling influenza. Changes in the viral surface proteins (antigenic variation), are largely responsible for the epidemiological success of the virus. Such an antigenic drift is caused by accumulations of point mutations in the viral genome. These variations render an individual susceptible to new strains, despite previous immunization or infection by other influenza viruses. Due to the constantly changing composition of influenza viruses in circulation, the influenza vaccine has to be modified every year to match the current viruses. Therefore, detailed knowledge about the circulating strains of influenza viruses is necessary. In order to gather these data, an international network has been created by the WHO. This network consists of 110 national and four global WHO collaborating centres. Data of weekly reports cover influenza activity as well as the number of influenza specimens isolated by type and subtype. The circulating influenza viruses have to be characterized serologically by the national centres, and a selection of strains has to be sent rapidly to the WHO collaborating centres for further strain identification. Results from the global influenza surveillance are reviewed each February and September.