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Lomholt FK, Emborg HD, Nørgaard SK, Nielsen J, Munkstrup C, Møller KL, Krog JS, Trebbien R, Vestergaard LS. Resurgence of Respiratory Syncytial Virus in the Summer of 2021 in Denmark-a Large out-of-season Epidemic Affecting Older Children. Open Forum Infect Dis 2024; 11:ofae069. [PMID: 38495773 PMCID: PMC10941316 DOI: 10.1093/ofid/ofae069] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2023] [Accepted: 02/02/2024] [Indexed: 03/19/2024] Open
Abstract
Background When coronavirus disease 2019 (COVID-19) restrictions were lifted in Denmark in the spring of 2021, a surge in respiratory syncytial virus (RSV) cases followed, causing a large out-of-season epidemic. This study aims to investigate the summer epidemic compared with 3 typical pre-COVID-19 RSV winter seasons using Danish registers to identify RSV cases, RSV-related admissions, and use of intensive care treatment. Methods Incidence rates (IR) per 1000 person-years for RSV cases, RSV-related admissions, and intensive care treatment were calculated with 95% confidence interval (CI) for each season, stratified by age groups and incidence rate ratios (IRR) with 95% CI were calculated to compare the summer epidemic with the winter season for 2019-2020. Results In the summer epidemic, the IR of RSV cases and admissions exceeded previous winter seasons for all age groups. The highest increases in IRs were seen among children aged 2 to 3 years and 4 to 5 years. The IRR of cases were 4.6 (95% CI, 4.1-5.2) and 3.3 (2.6-4.2) and the IRR of admissions were 3.3 (2.7-4.2) and 3.8 (2.3-6.5) in the 2 age groups, respectively, when compared with the winter season 2019-2020. Conclusions Likely because of immunity debt following COVID-19 restrictions, the summer epidemic was significantly larger than previous winter seasons, most markedly among children aged 2 to 3 and 4 to 5 years but had a similar disease severity spectrum.
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Affiliation(s)
| | - Hanne-Dorthe Emborg
- Department of Infections Disease Epidemiology and Prevention, Statens Serum Institut, Copenhagen, Denmark
| | - Sarah Kristine Nørgaard
- Department of Infections Disease Epidemiology and Prevention, Statens Serum Institut, Copenhagen, Denmark
| | - Jens Nielsen
- Department of Infections Disease Epidemiology and Prevention, Statens Serum Institut, Copenhagen, Denmark
| | - Charlotte Munkstrup
- Department of Infections Disease Epidemiology and Prevention, Statens Serum Institut, Copenhagen, Denmark
| | | | - Jesper Schak Krog
- Department of Virus and Microbiological Special Diagnostics, Statens Serum Institut, Copenhagen, Denmark
| | - Ramona Trebbien
- Department of Virus and Microbiological Special Diagnostics, Statens Serum Institut, Copenhagen, Denmark
| | - Lasse Skafte Vestergaard
- Department of Infections Disease Epidemiology and Prevention, Statens Serum Institut, Copenhagen, Denmark
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Emborg HD, Bolt Botnen A, Nielsen J, Vestergaard LS, Lomholt FK, Munkstrup C, Møller KL, Kjelsø C, Rasmussen SH, Trebbien R. Age-dependent influenza infection patterns and subtype circulation in Denmark, in seasons 2015/16 to 2021/22. Euro Surveill 2024; 29:2300263. [PMID: 38275020 PMCID: PMC10986648 DOI: 10.2807/1560-7917.es.2024.29.4.2300263] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2023] [Accepted: 09/19/2023] [Indexed: 01/27/2024] Open
Abstract
BackgroundInfluenza was almost absent for 2 years following the implementation of strict public health measures to prevent the spread of SARS-CoV-2. The consequence of this on infections in different age groups is not yet known.AimTo describe the age groups infected with the influenza virus in 2021/22, the first post-pandemic influenza season in Denmark, compared with the previous six seasons, and subtypes circulating therein.MethodsInfection and hospitalisation incidences per season and age group were estimated from data in Danish registries. Influenza virus subtypes and lineages were available from samples sent to the National Influenza Centre at Statens Serum Institut.ResultsTest incidence followed a similar pattern in all seasons, being highest in 0-1-year-olds and individuals over 75 years, and lowest in 7-14-year-olds and young people 15 years to late twenties. When the influenza A virus subtypes A(H3N2) and A(H1N1)pdm09 co-circulated in seasons 2015/16 and 2017/18 to 2019/20, the proportion of A(H1N1)pdm09 was higher in 0-1-year-olds and lower in the over 85-year-olds compared with the overall proportion of A(H1N1)pdm09 in these seasons. The proportion of A(H3N2) was higher in the over 85 years age group compared with the overall proportion of A(H3N2). The 2016/17 and 2021/22 seasons were dominated by A(H3N2) but differed in age-specific trends, with the over 85 years age group initiating the 2016/17 season, while the 2021/22 season was initiated by the 15-25-year-olds, followed by 7-14-year-olds.ConclusionThe 2021/22 influenza season had a different age distribution compared with pre-COVID-19 pandemic seasons.
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Affiliation(s)
- Hanne-Dorthe Emborg
- Department of Infectious Disease Epidemiology and Prevention, Statens Serum Institut, Denmark
| | - Amanda Bolt Botnen
- National Influenza Centre for WHO, Department of Virus and Microbiological Special Diagnostics, Statens Serum Institut, Denmark
| | - Jens Nielsen
- Department of Infectious Disease Epidemiology and Prevention, Statens Serum Institut, Denmark
| | - Lasse S Vestergaard
- Department of Infectious Disease Epidemiology and Prevention, Statens Serum Institut, Denmark
| | | | - Charlotte Munkstrup
- Department of Infectious Disease Epidemiology and Prevention, Statens Serum Institut, Denmark
| | | | - Charlotte Kjelsø
- Department of Infectious Disease Epidemiology and Prevention, Statens Serum Institut, Denmark
| | | | - Ramona Trebbien
- National Influenza Centre for WHO, Department of Virus and Microbiological Special Diagnostics, Statens Serum Institut, Denmark
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Munkstrup C, Lomholt FK, Emborg HD, Møller KL, Krog JS, Trebbien R, Vestergaard LS. Early and intense epidemic of respiratory syncytial virus (RSV) in Denmark, August to December 2022. Euro Surveill 2023; 28:2200937. [PMID: 36695451 PMCID: PMC9817209 DOI: 10.2807/1560-7917.es.2023.28.1.2200937] [Citation(s) in RCA: 25] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
In the autumn of 2022, Denmark witnessed the second out-of-season epidemic of respiratory syncytial virus (RSV) following widespread societal preventive measures implemented against the coronavirus disease (COVID-19) pandemic during 2020 and 2021. Admissions peaked at twice the level of pre-pandemic seasons. Especially infants below 6 months of age were affected, but also adults over 45 years of age. The current epidemic is dominated by RSV subtype B, unlike the major RSV summer epidemic in 2021 dominated by RSV subtype A.
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Affiliation(s)
- Charlotte Munkstrup
- Infectious Disease Epidemiology and Prevention, Statens Serum Institut, Copenhagen, Denmark
| | | | - Hanne-Dorthe Emborg
- Infectious Disease Epidemiology and Prevention, Statens Serum Institut, Copenhagen, Denmark
| | | | - Jesper Schak Krog
- Department of Virus and Microbiological Special Diagnostics, Statens Serum Institut, Copenhagen, Denmark
| | - Ramona Trebbien
- Department of Virus and Microbiological Special Diagnostics, Statens Serum Institut, Copenhagen, Denmark
| | - Lasse S. Vestergaard
- Infectious Disease Epidemiology and Prevention, Statens Serum Institut, Copenhagen, Denmark
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Larsen HD, Fonager J, Lomholt FK, Dalby T, Benedetti G, Kristensen B, Urth TR, Rasmussen M, Lassaunière R, Rasmussen TB, Strandbygaard B, Lohse L, Chaine M, Møller KL, Berthelsen ASN, Nørgaard SK, Sönksen UW, Boklund AE, Hammer AS, Belsham GJ, Krause TG, Mortensen S, Bøtner A, Fomsgaard A, Mølbak K. Preliminary report of an outbreak of SARS-CoV-2 in mink and mink farmers associated with community spread, Denmark, June to November 2020. ACTA ACUST UNITED AC 2021; 26. [PMID: 33541485 PMCID: PMC7863232 DOI: 10.2807/1560-7917.es.2021.26.5.210009] [Citation(s) in RCA: 92] [Impact Index Per Article: 30.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
In June–November 2020, SARS-CoV-2-infected mink were detected in 290 of 1,147 Danish mink farms. In North Denmark Region, 30% (324/1,092) of people found connected to mink farms tested SARS-CoV-2-PCR-positive and approximately 27% (95% confidence interval (CI): 25–30) of SARS-CoV-2-strains from humans in the community were mink-associated. Measures proved insufficient to mitigate spread. On 4 November, the government ordered culling of all Danish mink. Farmed mink constitute a potential virus reservoir challenging pandemic control.
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Affiliation(s)
| | | | | | - Tine Dalby
- Statens Serum Institut, Copenhagen, Denmark
| | | | | | | | | | | | | | | | | | | | | | | | | | | | - Anette Ella Boklund
- Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Anne Sofie Hammer
- Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Graham J Belsham
- Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | | | - Sten Mortensen
- Department of Animal Health, Danish Veterinary and Food administration, Copenhagen, Denmark
| | - Anette Bøtner
- Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Statens Serum Institut, Copenhagen, Denmark
| | | | - Kåre Mølbak
- Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Statens Serum Institut, Copenhagen, Denmark
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