Spotlight influenza: The 2019/20 influenza season and the impact of COVID-19 on influenza surveillance in the WHO European Region

Abstract

Background Annual 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. Aim We 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. Methods We 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. Results We 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. Conclusions Overall, 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.

Preparing for an influenza season 2021/22 with a likely co-circulation of influenza virus and SARS-CoV-2

“…In the Eurosurveillance Spotlight on influenza 2021 series, Adlhoch et al [ 5 ] report on epidemiological and virological surveillance of influenza in the 2019/20 season in Europe. An increasing number of countries did not report influenza data from weeks 12 or 13/2020 on, while many countries have maintained their influenza testing activities throughout the COVID-19 pandemic.…”

The impact of COVID-19 pandemic on influenza surveillance: a systematic review and meta-analysis

“…Meanwhile, about 1% of the total population in Germany and 2.5% of the total population in Spain are under sentinel influenza surveillance 19 . The comprehensive surveillance data from the WHO-European region was reported by Adlhoch et al 7 . The representative national network of primary care practitioners regularly conducts sentinel influenza surveillance among 1-6% of the WHO-European region population 20 .…”

“…The WHO European region testing a large number of influenza samples reported a decline in surveillance samples during the COVID-19 pandemic and the lowest number of influenza types and subtypes were noted since the establishment of GISRS in 1952. 7 In the US, the surveillance for influenza and the influenza test positivity rate declined by 61% and 98% respectively 2 . Similarly, the seasonal influenza positivity declined by 64% in China 22 and the sentinel surveillance of influenza was interrupted in the Lombardy region in Italy 23 .…”

A comparison of coronavirus disease 2019 and seasonal influenza surveillance in five European countries: France, Germany, Italy, Spain and the United Kingdom

“…Another effect of the burden of COVID‐19 is the reduction of influenza virological surveillance, which is critical to identify the strains for the next season's vaccine and could have real consequences on the efficacy of future seasonal influenza vaccines as well as pandemic preparedness 11,12,47 . The WHO has reviewed country experience in repurposing influenza surveillance systems in response to COVID‐19, aiming to develop interim recommendations on how to best sustain influenza sentinel surveillance 48 .…”

“…Another effect of the burden of COVID‐19 is the reduction of influenza virological surveillance, which is critical to identify the strains for the next season's vaccine and could have real consequences on the efficacy of future seasonal influenza vaccines as well as pandemic preparedness. 11 , 12 , 47 The WHO has reviewed country experience in repurposing influenza surveillance systems in response to COVID‐19, aiming to develop interim recommendations on how to best sustain influenza sentinel surveillance. 48 Similarly, the reduced circulation of influenza viruses, largely due to non‐pharmaceutical interventions introduced during the COVID‐19 pandemic, is likely to have consequences for the identification of influenza strains for future vaccines.…”