Abstract
BackgroundAnnual seasonal influenza activity in the northern hemisphere causes a high burden of disease during the winter months, peaking in the first weeks of the year.AimWe describe the 2019/20 influenza season and the impact of the COVID-19 pandemic on sentinel surveillance in the World Health Organization (WHO) European Region.MethodsWe analysed weekly epidemiological and virological influenza data from sentinel primary care and hospital sources reported by countries, territories and areas (hereafter countries) in the European Region.ResultsWe observed co-circulation of influenza B/Victoria-lineage, A(H1)pdm09 and A(H3) viruses during the 2019/20 season, with different dominance patterns observed across the Region. A higher proportion of patients with influenza A virus infection than type B were observed. The influenza activity started in week 47/2019, and influenza positivity rate was ≥ 50% for 2 weeks (05–06/2020) rather than 5–8 weeks in the previous five seasons. In many countries a rapid reduction in sentinel reports and the highest influenza activity was observed in weeks 09–13/2020. Reporting was reduced from week 14/2020 across the Region coincident with the onset of widespread circulation of SARS-CoV-2.ConclusionsOverall, influenza type A viruses dominated; however, there were varying patterns across the Region, with dominance of B/Victoria-lineage viruses in a few countries. The COVID-19 pandemic contributed to an earlier end of the influenza season and reduced influenza virus circulation probably owing to restricted healthcare access and public health measures.
Highlights
Influenza viruses cause seasonal epidemics with high burden and severity, as well as pandemics
First COVID-19 COVID-19 cases in Europe outbreak in COVID-19: coronavirus disease; PH: public health response; PHEIC: public health event of international concern. 10% line: 10% or higher was used as a threshold to determine the start of seasonal influenza activity; 50% line: 50% or higher was used as indicator for high influenza activity
Co-circulation of influenza A(H1)pdm09 and A(H3) viruses was observed in the previous seasons 2018/19, and viruses of the B/Victoria lineage circulated previously in 2015/16 [23]
Summary
Influenza viruses cause seasonal epidemics with high burden and severity, as well as pandemics. Territories and areas (hereafter referred to as countries) report syndromic, clinical and virological influenza surveillance data These include data from sentinel sources, where a representative number of primary care physicians systematically collect respiratory specimens for laboratory PCR testing from a subset of patients with either influenza-like illness (ILI) or acute respiratory infection (ARI) [13,14,15,16,17]. Some countries such as Norway use consultation data from a database/ register which covers the majority of the population. The COVID-19 pandemic contributed to an earlier end of the influenza season and reduced influenza virus circulation probably owing to restricted healthcare access and public health measures
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