Observational studyThe Lancet. Infectious diseases2022
Risk of hospitalisation associated with infection with SARS-CoV-2 omicron variant versus delta variant in Denmark: an observational cohort study.
Observational study in The Lancet. Infectious diseases, 2022. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 121 papers, 5 of them syntheses that pooled it.
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Who cites it
121 citing papers in PubMed, 5 syntheses or guidelines pooled it.
- Neutralising antibodies and protection from progression to severe COVID-19: A meta-analysis.PLoS medicine · 2026Pooled it
- Comparison of Omicron and Delta Variants of SARS-CoV-2: A Systematic Review of Current Evidence.Infectious disorders drug targets · 2024Pooled it
- Clinical outcomes of the severe acute respiratory syndrome coronavirus 2 Omicron and Delta variant: systematic review and meta-analysis of 33 studies covering 6 037 144 coronavirus disease 2019-positive patients.Clinical microbiology and infection : the official publication of the European Society of Clinical Microbiology and Infectious Diseases · 2023Pooled it
- Severity and outcomes of Omicron variant of SARS-CoV-2 compared to Delta variant and severity of Omicron sublineages: a systematic review and metanalysis.BMJ global health · 2023Pooled it
- COVID-19 vaccines reduce the risk of SARS-CoV-2 reinfection and hospitalization: Meta-analysis.Frontiers in medicine · 2022Pooled it
- The burden of COVID-19-related intensive care admissions in the Nordic countries, 2020-2023.BMC infectious diseases · 2026Article
- Article
- The High Expression of PD-1 Defines A Subpopulation of Tfh Cells Responding to COVID-19 Vaccine in Humans.Genomics, proteomics & bioinformatics · 2025Article
- Article
- Convergent Evolution and Host-Limiting Impacts of SARS-CoV-2 Revealed by Cellular Experiments.Molecular biology and evolution · 2025Article
- Impact of SARS-CoV-2 Infection on the Course of Pregnancy and Birth After Assisted Reproduction.Geburtshilfe und Frauenheilkunde · 2025Article
- COVID-19 infection and severity among childhood cancer survivors in Denmark and Sweden: a register-based cohort study with matched population and sibling comparisons.The Lancet regional health. Europe · 2025Article
- Dissecting Sex-Specific Pathology in K18-hACE2 Transgenic Mice Infected With Different SARS-CoV-2 Variants.Journal of medical virology · 2025Article
- Long Covid Symptom Clusters, Correlates and Predictors in a Highly Vaccinated Australian Population in 2023.Health expectations : an international journal of public participation in health care and health policy · 2025Article
- Characteristics and predictors of severe outcomes of COVID-19 cases presenting to the emergency department of a major Australian referral hospital: A record linkage study.Emergency medicine Australasia : EMA · 2025Article
- Longitudinal analysis of Covid-19 infection trends and in-hospital mortality across six pandemic waves in Tunisia.Archives of public health = Archives belges de sante publique · 2025Article
- Allosteric Control and Glycan Shielding Adaptations in the SARS-CoV-2 Spike from Early to Peak Virulence.bioRxiv : the preprint server for biology · 2025Article
- SARS-CoV-2 Variants: Genetic Insights, Epidemiological Tracking, and Implications for Vaccine Strategies.International journal of molecular sciences · 2025Review
- Insights into Omicron: Genomic Characterization and Inpatient Risk Assessment at Single Tertiary Hospital in Indonesia.Journal of multidisciplinary healthcare · 2025Article
- Omicron surge impact on acute kidney injury in ICU patients: A study using the ISARIC COVID-19 database.PloS one · 2025Observational
61 more citing papers are in PubMed but not listed here.
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21 authors.
Funding
Abstract
backgroundEstimates 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.
methodsIn 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.
findingsBetween 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.
interpretationWe 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.
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