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. 2021 Jun;26(22):2001160.
doi: 10.2807/1560-7917.ES.2021.26.22.2001160.

Abrupt termination of the 2019/20 influenza season following preventive measures against COVID-19 in Denmark, Norway and Sweden

Hanne-Dorthe Emborg  1 , AnnaSara Carnahan  2 , Karoline Bragstad  3 , Ramona Trebbien  1 , Mia Brytting  2 , Olav Hungnes  3 , Emma Byström  2 , Lasse S Vestergaard  1
Affiliations

Abrupt termination of the 2019/20 influenza season following preventive measures against COVID-19 in Denmark, Norway and Sweden

Hanne-Dorthe Emborg et al. Euro Surveill. 2021 Jun.

Abstract

BackgroundIn mid-March 2020, a range of public health and social measures (PHSM) against the then new coronavirus disease (COVID-19) were implemented in Denmark, Norway and Sweden.AimWe analysed the development of influenza cases during the implementation of PHSM against SARS-CoV-2 in the Scandinavian countries.MethodBased on the established national laboratory surveillance of influenza, we compared the number of human influenza cases in the weeks immediately before and after the implementation of SARS-CoV-2 PHSM by country. The 2019/20 influenza season was compared with the five previous seasons.ResultsA dramatic reduction in influenza cases was seen in all three countries, with only a 3- to 6-week duration from the peak of weekly influenza cases until the percentage dropped below 1%. In contrast, in the previous nine influenza seasons, the decline from the seasonal peak to below 1% of influenza-positive samples took more than 10 weeks.ConclusionsThe PHSM against SARS-CoV-2 were followed by a dramatic reduction in influenza cases, indicating a wider public health effect of the implemented measures.

Keywords: COVID-19; Scandinavian countries; impact preventive measures; influenza.

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Conflict of interest statement

Conflict of interest: None declared.

Figures

Figure 1
Figure 1
Interventions implemented to reduce the transmission of SARS-CoV-2 in Denmark, Norway and Sweden, 9–22 March 2020
Figure 2
Figure 2
Laboratory-confirmed influenza A and B in Denmark, Norway and Sweden, 30 September 2019–5 April 2020
Figure 3
Figure 3
Percentage of influenza-positive samples per week in Denmark, Norway and Sweden, influenza seasons 2014/15–2019/20
See this image and copyright information in PMC

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