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Risk of hospitalisation associated with infection with SARS-CoV-2 omicron variant versus delta variant in Denmark: an observational cohort study.
Bager, Peter; Wohlfahrt, Jan; Bhatt, Samir; Stegger, Marc; Legarth, Rebecca; Møller, Camilla Holten; Skov, Robert Leo; Valentiner-Branth, Palle; Voldstedlund, Marianne; Fischer, Thea K; Simonsen, Lone; Kirkby, Nikolai Søren; Thomsen, Marianne Kragh; Spiess, Katja; Marving, Ellinor; Larsen, Nicolai Balle; Lillebaek, Troels; Ullum, Henrik; Mølbak, Kåre; Krause, Tyra Grove.
  • Bager P; Division of Infectious Disease Preparedness, Statens Serum Institut, Copenhagen, Denmark. Electronic address: pbg@ssi.dk.
  • Wohlfahrt J; Department of Epidemiology Research, Statens Serum Institut, Copenhagen, Denmark.
  • Bhatt S; Section of Epidemiology, University of Copenhagen, Copenhagen, Denmark; MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, London, UK; The Abdul Latif Jameel Institute for Disease and Emergency Analytics, School of Public Health, Imperial College Lon
  • Stegger M; Department of Bacteria, Parasites, and Fungi, Statens Serum Institut, Copenhagen, Denmark.
  • Legarth R; Division of Infectious Disease Preparedness, Statens Serum Institut, Copenhagen, Denmark.
  • Møller CH; Division of Infectious Disease Preparedness, Statens Serum Institut, Copenhagen, Denmark.
  • Skov RL; Division of Infectious Disease Preparedness, Statens Serum Institut, Copenhagen, Denmark.
  • Valentiner-Branth P; Division of Infectious Disease Preparedness, Statens Serum Institut, Copenhagen, Denmark.
  • Voldstedlund M; Division of Infectious Disease Preparedness, Statens Serum Institut, Copenhagen, Denmark.
  • Fischer TK; Department of Public Health, University of Copenhagen, Copenhagen, Denmark; Department of Clinical Research, Nordsjaellands Hospital, Hillerød, Denmark.
  • Simonsen L; PandemiX Center, Department of Science and Environment, Roskilde University, Roskilde, Denmark.
  • Kirkby NS; Department of Clinical Microbiology, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark.
  • Thomsen MK; Department of Clinical Microbiology, Aarhus University Hospital, Aarhus, Denmark.
  • Spiess K; Department of Virus & Microbiological Special Diagnostics, Statens Serum Institut, Copenhagen, Denmark.
  • Marving E; Department of Virus & Microbiological Special Diagnostics, Statens Serum Institut, Copenhagen, Denmark.
  • Larsen NB; Department of Virus & Microbiological Special Diagnostics, Statens Serum Institut, Copenhagen, Denmark; Test Center Danmark, Statens Serum Institut, Copenhagen, Denmark.
  • Lillebaek T; International Reference Laboratory of Mycobacteriology, Statens Serum Institut, Copenhagen, Denmark; Global Health Section, University of Copenhagen, Copenhagen, Denmark.
  • Ullum H; Division of Infectious Disease Preparedness, Statens Serum Institut, Copenhagen, Denmark.
  • Mølbak K; Division of Infectious Disease Preparedness, Statens Serum Institut, Copenhagen, Denmark; Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
  • Krause TG; Division of Infectious Disease Preparedness, Statens Serum Institut, Copenhagen, Denmark.
Lancet Infect Dis ; 22(7): 967-976, 2022 07.
Article in English | MEDLINE | ID: covidwho-1799640
ABSTRACT

BACKGROUND:

Estimates of the severity of the SARS-CoV-2 omicron variant (B.1.1.529) are crucial to assess the public health impact associated with its rapid global dissemination. We estimated the risk of SARS-CoV-2-related hospitalisations after infection with omicron compared with the delta variant (B.1.617.2) in Denmark, a country with high mRNA vaccination coverage and extensive free-of-charge PCR testing capacity.

METHODS:

In this observational cohort study, we included all RT-PCR-confirmed cases of SARS-CoV-2 infection in Denmark, with samples taken between Nov 21 (date of first omicron-positive sample) and Dec 19, 2021. Individuals were identified in the national COVID-19 surveillance system database, which included results of a variant-specific RT-PCR that detected omicron cases, and data on SARS-CoV-2-related hospitalisations (primary outcome of the study). We calculated the risk ratio (RR) of hospitalisation after infection with omicron compared with delta, overall and stratified by vaccination status, in a Poisson regression model with robust SEs, adjusted a priori for reinfection status, sex, age, region, comorbidities, and time period.

FINDINGS:

Between Nov 21 and Dec 19, 2021, among the 188 980 individuals with SARS-CoV-2 infection, 38 669 (20·5%) had the omicron variant. SARS-CoV-2-related hospitalisations and omicron cases increased during the study period. Overall, 124 313 (65·8%) of 188 980 individuals were vaccinated, and vaccination was associated with a lower risk of hospitalisation (adjusted RR 0·24, 95% CI 0·22-0·26) compared with cases with no doses or only one dose of vaccine. Compared with delta infection, omicron infection was associated with an adjusted RR of hospitalisation of 0·64 (95% CI 0·56-0·75; 222 [0·6%] of 38 669 omicron cases admitted to hospital vs 2213 [1·5%] of 150 311 delta cases). For a similar comparison by vaccination status, the RR of hospitalisation was 0·57 (0·44-0·75) among cases with no or only one dose of vaccine, 0·71 (0·60-0·86) among those who received two doses, and 0·50 (0·32-0·76) among those who received three doses.

INTERPRETATION:

We found a significantly lower risk of hospitalisation with omicron infection compared with delta infection among both vaccinated and unvaccinated individuals, suggesting an inherent reduced severity of omicron. Our results could guide modelling of the effect of the ongoing global omicron wave and thus health-care system preparedness.

FUNDING:

None.
Subject(s)

Full text: Available Collection: International databases Database: MEDLINE Main subject: Hepatitis D / COVID-19 Type of study: Cohort study / Observational study / Prognostic study Topics: Vaccines / Variants Limits: Humans Country/Region as subject: Europa Language: English Journal: Lancet Infect Dis Journal subject: Communicable Diseases Year: 2022 Document Type: Article

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Full text: Available Collection: International databases Database: MEDLINE Main subject: Hepatitis D / COVID-19 Type of study: Cohort study / Observational study / Prognostic study Topics: Vaccines / Variants Limits: Humans Country/Region as subject: Europa Language: English Journal: Lancet Infect Dis Journal subject: Communicable Diseases Year: 2022 Document Type: Article