Abstract
BackgroundInfluenza virus infections are common and lead to substantial morbidity and mortality worldwide. We characterized the first eight influenza epidemics since the 2009 influenza pandemic by describing the distribution of viruses and epidemics temporally and geographically across the WHO European Region.MethodsWe retrospectively analyzed laboratory‐confirmed influenza detections in ambulatory patients from sentinel sites. Data were aggregated by reporting entity and season (weeks 40‐20) for 2010‐2011 to 2017‐2018. We explored geographical spread using correlation coefficients.ResultsThere was variation in the regional influenza epidemics during the study period. Influenza A virus subtypes alternated in dominance, except for 2013‐2014 during which both cocirculated, and only one season (2017‐2018) was B virus dominant. The median start week for epidemics in the Region was week 50, the time to the peak ranged between four and 13 weeks, and the duration of the epidemic ranged between 19 and 25 weeks. There was evidence of a west‐to‐east spread across the Region during epidemics in 2010‐2011 (r = .365; P = .019), 2012‐2013 (r = .484; P = .001), 2014‐2015 (r = .423; P = .006), and 2017‐2018 (r = .566; P < .001) seasons. Variation in virus distribution and timing existed within reporting entities across seasons and across reporting entities for a given season.ConclusionsAggregated influenza detection data from sentinel surveillance sites by season between 2010 and 2018 have been presented for the European Region for the first time. Substantial diversity exists between influenza epidemics. These data can inform prevention and control efforts at national, sub‐national, and international levels. Aggregated, regional surveillance data from early affected reporting entities may provide an early warning function and be helpful for early season forecasting efforts.
Highlights
Influenza virus infections are common and lead to substantial morbidity and mortality[1] worldwide
Sentinel influenza surveillance is conducted in a representative subset of outpatient sites and coordinated by national networks; samples should be collected from patients using a systematic sampling scheme with pre-defined influenza-like illness (ILI) and/or acute respiratory infection (ARI) case definitions
Over eight influenza seasons following the 2009 pandemic, we characterized influenza virus detections from sentinel surveillance in outpatients and found that annual epidemics of influenza in the European Region exhibited some patterns
Summary
Influenza virus infections are common and lead to substantial morbidity and mortality[1] worldwide. Influenza surveillance is conducted nationally (sometimes sub-nationally), supra-nationally, and globally with a range of objectives which include determining when and where influenza activity is occurring, identifying the circulating influenza type, A subtype and B lineage, detecting changes in the antigenic and genetic characteristics of seasonal influenza viruses to inform the composition of influenza vaccines biannually,[2] and describing the clinical patterns of influenza. Collated data on influenza activity for the Region are analyzed and, since 2014, reported weekly in the joint Flu News Europe bulletin during the influenza season.[4]. To further inform evidence-based decision making for influenza preparedness and control, we characterized the first eight influenza seasons following the 2009 influenza pandemic in terms of virus distribution by type, subtype and lineage, age, timing, and geographical spread
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