End of the 2016–2017 influenza season

Flu News Europe

Countries conduct surveillance to characterize the circulating influenza viruses, to determine the timing of the influenza season and the potential severity of disease, and to provide data to WHO for regional and global updates.

WHO/Europe and the European Centre for Disease Prevention and Control (ECDC) collaborate to collect and analyse influenza surveillance data from WHO European Member States, and to present these data each week in the Flu News Europe bulletin. Knowing how influenza is spreading through the WHO European Region (often in a west–east pattern) and which virus predominates helps prepare countries for the peak of the season, when health services may become overburdened by the number of patients.

The last weekly bulletin for the 2016–2017 influenza season was published on 26 June 2017. Monthly bulletins will be published over the summer months before weekly reporting recommences for the 2017–2018 season on 6 October 2017.

Key features of the 2016–2017 influenza season

After an earlier start than usual (week 46/2016) and no clear pattern in spread across the Region, influenza activity peaked between weeks 52/2016 and 4/2017. From week 12/2017, most countries reported decreased influenza activity. The proportion of sentinel detections returned to the epidemic threshold value (10%) in week 17/2017.

From week 40/2016 to week 10/2017, influenza A viruses predominated, accounting for 90% of all sentinel detections. Of those subtyped, 99% were A(H3N2). Influenza B viruses predominated after week 11/2017, although absolute numbers of type B detections remained low and decreased from week 14/2017.

Confirmed cases of influenza A virus infection reported from hospitals were predominantly in adults aged 65 years or older. In the majority of the 20 reporting countries or regions, significant excess all-cause mortality was observed in people aged 15–64 years, and markedly so in people aged 65 years or older. This is commonly seen when the predominant circulating viruses are A(H3N2).

Two thirds of the genetically characterized A(H3N2) viruses belonged to subclade 3C.2a1, but remained antigenically similar to the clade 3C.2a vaccine virus, as described in the WHO recommendations for vaccine composition for the northern hemisphere’s 2017–2018 influenza season. More information is also available in the February 2017 report of the WHO Collaborating Centre for Reference and Research on Influenza at the Francis Crick Institute (United Kingdom).

Vaccine effectiveness estimates for all age groups against A(H3N2) illness suggested moderate effectiveness in Canada (42%), the United States of America (43%) and Europe (38%).

Few influenza viruses tested over the season showed reduced susceptibility to oseltamivir and/or zanamivir.

Plans for the upcoming season

In preparation for the upcoming influenza season, WHO/Europe and ECDC will continue to collaborate on further improving the surveillance system platform and outputs.

ECDC is also holding its Annual Influenza Meeting on 20–22 June 2017 in Stockholm, Sweden. The event will bring together representatives from the 31 European Union/European Economic Area Member States as well as Albania, Bosnia and Herzegovina, Israel, Kosovo (in accordance with United Nations Security Council Resolution 1244 [1999]), Serbia, Switzerland, the former Yugoslav Republic of Macedonia and Turkey.

The Meeting will focus on new developments in influenza surveillance at the country and regional level, and on seasonal influenza vaccination programmes. It will provide an update on the global situation with regard to outbreaks of avian influenza and other emerging respiratory pathogens, and serve as a forum for exchanging experiences from the past influenza season. Representatives from WHO/Europe, who contributed to developing the Meeting agenda, will also be present.