Start of regional influenza surveillance for the 2017–2018 season

During the winter months, influenza may infect up to 20% of the population, depending on which viruses are circulating, and cause substantial mortality. People at increased risk for severe disease once infected include the elderly, pregnant women, young children, immunocompromised people and people with chronic underlying medical conditions. These groups represent a significant proportion of the population in the WHO European Region. WHO recommends that everyone at risk of severe disease as a result of infection with influenza, as well as health-care workers, be offered a seasonal influenza vaccine.

As it is not possible to predict if one influenza virus will predominate in a particular season, seasonal influenza vaccines cover all viruses that are anticipated to circulate, namely influenza A(H3N2), influenza A(H1N1) and influenza B. Due to the constantly changing nature of these viruses – known as antigenic drift – recommendations on the composition of influenza vaccines for use in the northern and southern hemisphere influenza seasons are made each year.

Countries conduct virological and clinical surveillance of influenza to characterize the circulating influenza viruses, and to determine the timing of the influenza season and the potential severity of disease – all of which might differ from one season to the next. They provide these data to WHO for regional and global updates.

Each week during the influenza season (weeks 40 to 20), WHO/Europe, in collaboration with the European Centre for Disease Prevention and Control, collects and analyses influenza surveillance data from Member States and publishes the Flu News Europe bulletin. These surveillance outputs provide public health specialists and decision-makers in Member States with the information required to assess influenza activity in the Region and take appropriate action. The early bulletins for this season indicate low levels of influenza activity in the Region.

Knowing how influenza is spreading through the Region (often in a west-to-east pattern) and which virus predominates helps countries prepare for the peak of the season, when health services may become overburdened. It also helps them determine which segments of the population might be most affected.

Influenza A(H3N2) virus is known to cause severe disease and death in the elderly, while influenza A(H1N1) virus, which caused the 2009 pandemic and which now circulates as seasonal influenza, is more likely to cause severe disease in younger age groups.

Monitoring influenza virus circulation across the Region also informs recommendations on the composition of influenza vaccines. Details of the recent recommendations on the vaccine composition for use in the 2018 southern hemisphere influenza season can be found on WHO Headquarters’ website.