Reduced risk of hospitalisation associated with infection with SARS-CoV-2 Omicron relative to Delta: A Danish cohort study

Peter Bager; Jan Wohlfahrt; Samir Bhatt; Sofie Marie Edslev; Raphael Niklaus  Sieber; Anna Cäcilia Ingham; Marc Stegger; Rebecca Legarth; Camilla Holten Møller; Robert Leo Skov; Palle Valentiner-Branth; Maria Overvad; Mie Agermose Gram; Frederikke Kristensen Lomholt; Louise Hallundbæk; Caroline Hjorth Espensen; Sophie Gubbels; Marianne Voldstedlund; Marianne Karakis; Karina Lauenborg Møller; Stefan Schytte Olsen; Thea K. Fischer; Zitta Barrella Harboe; Caroline Klint Johannesen; Maarten van Wijhe; Jon Gitz Holler; Lone Simonsen; Ram Benny Christian Dessau; Martin Barfred Friis; David Fuglsang-Damgaard; Mette Pinholt; Nikolai Søren Kirkby; Marianne Kragh Thomsen; Thomas Vognbjerg Sydenham; John Eugenio Coia; Ea Sofie Marmolin; Anders Fomsgaard; Jannik Fonager; Morten Rasmussen; Katja Spiess; Ellinor Marving; Arieh Cohen; Nicolai Balle Larsen; Troels Lillebaek; Henrik Ullum; Kåre Mølbak; Tyra Grove Krause

doi:10.2139/ssrn.4008930

Reduced risk of hospitalisation associated with infection with SARS-CoV-2 Omicron relative to Delta: A Danish cohort study

Peter Bager^*, Jan Wohlfahrt, Samir Bhatt, Sofie Marie Edslev, Raphael Niklaus Sieber, Anna Cäcilia Ingham, Marc Stegger, Rebecca Legarth, Camilla Holten Møller, Robert Leo Skov, Palle Valentiner-Branth, Maria Overvad, Mie Agermose Gram, Frederikke Kristensen Lomholt, Louise Hallundbæk, Caroline Hjorth Espensen, Sophie Gubbels, Marianne Voldstedlund, Marianne Karakis, Karina Lauenborg MøllerStefan Schytte Olsen, Thea K. Fischer, Zitta Barrella Harboe, Caroline Klint Johannesen, Maarten van Wijhe, Jon Gitz Holler, Lone Simonsen, Ram Benny Christian Dessau, Martin Barfred Friis, David Fuglsang-Damgaard, Mette Pinholt, Nikolai Søren Kirkby, Marianne Kragh Thomsen, Thomas Vognbjerg Sydenham, John Eugenio Coia, Ea Sofie Marmolin, Anders Fomsgaard, Jannik Fonager, Morten Rasmussen, Katja Spiess, Ellinor Marving, Arieh Cohen, Nicolai Balle Larsen, Troels Lillebaek, Henrik Ullum, Kåre Mølbak, Tyra Grove Krause

^*Corresponding author for this work

Research output: Working paper › Preprint

Abstract

Background: Estimates of the severity of the emerging Omicron variant are critical 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 Delta in Denmark, a country with high mRNA vaccination coverage and an extensive free-of-charge PCR test capacity.
Methods: Observational cohort study of all RT-PCR SARS-CoV-2 positive individuals in Denmark between 21 November and 19 December, 2021, the period Omicron emerged while Delta was still dominant. Individuals were identified in the national COVID-19 surveillance system database which include results of a variant specific RT- PCR detecting Omicron cases, SARS-CoV-2 related hospitalisations (primary outcome of the study). The risk ratio (RR) of hospitalisation after infection with Omicron compared with Delta, overall and stratified by vaccination status, was calculated in a Poisson regression model with robust standard errors, adjusted à priori for reinfection status, sex, age, region, comorbidities, and period.
Findings: Among the 188,980 SARS-CoV-2 infected individuals, 38,669 (20.1%) were Omicron vPCR positive. SARS-CoV-2 related hospitalisations and Omicron cases increased during the study period. Overall, 124,313 (65.8 %) 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 or one vaccination. Compared with Delta infection, Omicron was associated with an adjusted RR of hospitalisation of 0.64 (95%CI 0.56-0.75; 222 Omicron and 2,213 Delta hospitalisations). For the similar comparison by vaccination status, the RR of hospitalisation was 0.57 (95%CI 0.44- 0.75) among cases with no or one vaccination, 0.71 (95%CI 0.60-0.86) among two- dose vaccinated, and 0.50 (95%CI 0.32-0.76) among three-dose vaccinated. Interpretation: We found a significantly lower risk of hospitalisation with Omicron infection compared with Delta among both vaccinated and unvaccinated individuals, suggesting an inherent reduced severity of Omicron. Our results can guide modelling of the impact of the ongoing global Omicron wave and thus health care system preparedness.

Original language	English
Place of Publication	The Lancet Infectious Diseases
Publisher	The Lancet Publishing Group
DOIs	https://doi.org/10.2139/ssrn.4008930
Publication status	Published - 22 Apr 2022

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10.2139/ssrn.4008930

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Bager, P., Wohlfahrt, J., Bhatt, S., Edslev, S. M., Sieber, R. N., Ingham, A. C., Stegger, M., Legarth, R., Møller, C. H., Skov, R. L., Valentiner-Branth, P., Overvad, M., Agermose Gram, M., Kristensen Lomholt, F., Hallundbæk, L., Hjorth Espensen, C., Gubbels, S., Voldstedlund, M., Karakis, M., ... Grove Krause, T. (2022). Reduced risk of hospitalisation associated with infection with SARS-CoV-2 Omicron relative to Delta: A Danish cohort study. The Lancet Publishing Group. https://doi.org/10.2139/ssrn.4008930

@techreport{91a25ccaed92462baf98c153933081bd,

title = "Reduced risk of hospitalisation associated with infection with SARS-CoV-2 Omicron relative to Delta: A Danish cohort study",

abstract = "Background: Estimates of the severity of the emerging Omicron variant are critical 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 Delta in Denmark, a country with high mRNA vaccination coverage and an extensive free-of-charge PCR test capacity.Methods: Observational cohort study of all RT-PCR SARS-CoV-2 positive individuals in Denmark between 21 November and 19 December, 2021, the period Omicron emerged while Delta was still dominant. Individuals were identified in the national COVID-19 surveillance system database which include results of a variant specific RT- PCR detecting Omicron cases, SARS-CoV-2 related hospitalisations (primary outcome of the study). The risk ratio (RR) of hospitalisation after infection with Omicron compared with Delta, overall and stratified by vaccination status, was calculated in a Poisson regression model with robust standard errors, adjusted {\`a} priori for reinfection status, sex, age, region, comorbidities, and period.Findings: Among the 188,980 SARS-CoV-2 infected individuals, 38,669 (20.1%) were Omicron vPCR positive. SARS-CoV-2 related hospitalisations and Omicron cases increased during the study period. Overall, 124,313 (65.8 %) 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 or one vaccination. Compared with Delta infection, Omicron was associated with an adjusted RR of hospitalisation of 0.64 (95%CI 0.56-0.75; 222 Omicron and 2,213 Delta hospitalisations). For the similar comparison by vaccination status, the RR of hospitalisation was 0.57 (95%CI 0.44- 0.75) among cases with no or one vaccination, 0.71 (95%CI 0.60-0.86) among two- dose vaccinated, and 0.50 (95%CI 0.32-0.76) among three-dose vaccinated. Interpretation: We found a significantly lower risk of hospitalisation with Omicron infection compared with Delta among both vaccinated and unvaccinated individuals, suggesting an inherent reduced severity of Omicron. Our results can guide modelling of the impact of the ongoing global Omicron wave and thus health care system preparedness.",

author = "Peter Bager and Jan Wohlfahrt and Samir Bhatt and Edslev, {Sofie Marie} and Sieber, {Raphael Niklaus} and Ingham, {Anna C{\"a}cilia} and Marc Stegger and Rebecca Legarth and M{\o}ller, {Camilla Holten} and Skov, {Robert Leo} and Palle Valentiner-Branth and Maria Overvad and {Agermose Gram}, Mie and {Kristensen Lomholt}, Frederikke and Louise Hallundb{\ae}k and {Hjorth Espensen}, Caroline and Sophie Gubbels and Marianne Voldstedlund and Marianne Karakis and {Lauenborg M{\o}ller}, Karina and {Schytte Olsen}, Stefan and {K. Fischer}, Thea and {Barrella Harboe}, Zitta and {Klint Johannesen}, Caroline and {van Wijhe}, Maarten and {Gitz Holler}, Jon and Lone Simonsen and {Benny Christian Dessau}, Ram and {Barfred Friis}, Martin and David Fuglsang-Damgaard and Mette Pinholt and {S{\o}ren Kirkby}, Nikolai and {Kragh Thomsen}, Marianne and {Vognbjerg Sydenham}, Thomas and {Eugenio Coia}, John and {Sofie Marmolin}, Ea and Anders Fomsgaard and Jannik Fonager and Morten Rasmussen and Katja Spiess and Ellinor Marving and Arieh Cohen and {Balle Larsen}, Nicolai and Troels Lillebaek and Henrik Ullum and K{\aa}re M{\o}lbak and {Grove Krause}, Tyra",

year = "2022",

month = apr,

day = "22",

doi = "10.2139/ssrn.4008930",

language = "English",

publisher = "The Lancet Publishing Group",

type = "WorkingPaper",

institution = "The Lancet Publishing Group",

}

Bager, P, Wohlfahrt, J, Bhatt, S, Edslev, SM, Sieber, RN, Ingham, AC, Stegger, M, Legarth, R, Møller, CH, Skov, RL, Valentiner-Branth, P, Overvad, M, Agermose Gram, M, Kristensen Lomholt, F, Hallundbæk, L, Hjorth Espensen, C, Gubbels, S, Voldstedlund, M, Karakis, M, Lauenborg Møller, K, Schytte Olsen, S, K. Fischer, T, Barrella Harboe, Z, Klint Johannesen, C, van Wijhe, M, Gitz Holler, J, Simonsen, L, Benny Christian Dessau, R, Barfred Friis, M, Fuglsang-Damgaard, D, Pinholt, M, Søren Kirkby, N, Kragh Thomsen, M, Vognbjerg Sydenham, T, Eugenio Coia, J, Sofie Marmolin, E, Fomsgaard, A, Fonager, J, Rasmussen, M, Spiess, K, Marving, E, Cohen, A, Balle Larsen, N, Lillebaek, T, Ullum, H, Mølbak, K & Grove Krause, T 2022 'Reduced risk of hospitalisation associated with infection with SARS-CoV-2 Omicron relative to Delta: A Danish cohort study' The Lancet Publishing Group, The Lancet Infectious Diseases. https://doi.org/10.2139/ssrn.4008930

TY - UNPB

T1 - Reduced risk of hospitalisation associated with infection with SARS-CoV-2 Omicron relative to Delta

T2 - A Danish cohort study

AU - Bager, Peter

AU - Wohlfahrt, Jan

AU - Bhatt, Samir

AU - Edslev, Sofie Marie

AU - Sieber, Raphael Niklaus

AU - Ingham, Anna Cäcilia

AU - Stegger, Marc

AU - Legarth, Rebecca

AU - Møller, Camilla Holten

AU - Skov, Robert Leo

AU - Valentiner-Branth, Palle

AU - Overvad, Maria

AU - Agermose Gram, Mie

AU - Kristensen Lomholt, Frederikke

AU - Hallundbæk, Louise

AU - Hjorth Espensen, Caroline

AU - Gubbels, Sophie

AU - Voldstedlund, Marianne

AU - Karakis, Marianne

AU - Lauenborg Møller, Karina

AU - Schytte Olsen, Stefan

AU - K. Fischer, Thea

AU - Barrella Harboe, Zitta

AU - Klint Johannesen, Caroline

AU - van Wijhe, Maarten

AU - Gitz Holler, Jon

AU - Simonsen, Lone

AU - Benny Christian Dessau, Ram

AU - Barfred Friis, Martin

AU - Fuglsang-Damgaard, David

AU - Pinholt, Mette

AU - Søren Kirkby, Nikolai

AU - Kragh Thomsen, Marianne

AU - Vognbjerg Sydenham, Thomas

AU - Eugenio Coia, John

AU - Sofie Marmolin, Ea

AU - Fomsgaard, Anders

AU - Fonager, Jannik

AU - Rasmussen, Morten

AU - Spiess, Katja

AU - Marving, Ellinor

AU - Cohen, Arieh

AU - Balle Larsen, Nicolai

AU - Lillebaek, Troels

AU - Ullum, Henrik

AU - Mølbak, Kåre

AU - Grove Krause, Tyra

PY - 2022/4/22

Y1 - 2022/4/22

N2 - Background: Estimates of the severity of the emerging Omicron variant are critical 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 Delta in Denmark, a country with high mRNA vaccination coverage and an extensive free-of-charge PCR test capacity.Methods: Observational cohort study of all RT-PCR SARS-CoV-2 positive individuals in Denmark between 21 November and 19 December, 2021, the period Omicron emerged while Delta was still dominant. Individuals were identified in the national COVID-19 surveillance system database which include results of a variant specific RT- PCR detecting Omicron cases, SARS-CoV-2 related hospitalisations (primary outcome of the study). The risk ratio (RR) of hospitalisation after infection with Omicron compared with Delta, overall and stratified by vaccination status, was calculated in a Poisson regression model with robust standard errors, adjusted à priori for reinfection status, sex, age, region, comorbidities, and period.Findings: Among the 188,980 SARS-CoV-2 infected individuals, 38,669 (20.1%) were Omicron vPCR positive. SARS-CoV-2 related hospitalisations and Omicron cases increased during the study period. Overall, 124,313 (65.8 %) 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 or one vaccination. Compared with Delta infection, Omicron was associated with an adjusted RR of hospitalisation of 0.64 (95%CI 0.56-0.75; 222 Omicron and 2,213 Delta hospitalisations). For the similar comparison by vaccination status, the RR of hospitalisation was 0.57 (95%CI 0.44- 0.75) among cases with no or one vaccination, 0.71 (95%CI 0.60-0.86) among two- dose vaccinated, and 0.50 (95%CI 0.32-0.76) among three-dose vaccinated. Interpretation: We found a significantly lower risk of hospitalisation with Omicron infection compared with Delta among both vaccinated and unvaccinated individuals, suggesting an inherent reduced severity of Omicron. Our results can guide modelling of the impact of the ongoing global Omicron wave and thus health care system preparedness.

AB - Background: Estimates of the severity of the emerging Omicron variant are critical 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 Delta in Denmark, a country with high mRNA vaccination coverage and an extensive free-of-charge PCR test capacity.Methods: Observational cohort study of all RT-PCR SARS-CoV-2 positive individuals in Denmark between 21 November and 19 December, 2021, the period Omicron emerged while Delta was still dominant. Individuals were identified in the national COVID-19 surveillance system database which include results of a variant specific RT- PCR detecting Omicron cases, SARS-CoV-2 related hospitalisations (primary outcome of the study). The risk ratio (RR) of hospitalisation after infection with Omicron compared with Delta, overall and stratified by vaccination status, was calculated in a Poisson regression model with robust standard errors, adjusted à priori for reinfection status, sex, age, region, comorbidities, and period.Findings: Among the 188,980 SARS-CoV-2 infected individuals, 38,669 (20.1%) were Omicron vPCR positive. SARS-CoV-2 related hospitalisations and Omicron cases increased during the study period. Overall, 124,313 (65.8 %) 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 or one vaccination. Compared with Delta infection, Omicron was associated with an adjusted RR of hospitalisation of 0.64 (95%CI 0.56-0.75; 222 Omicron and 2,213 Delta hospitalisations). For the similar comparison by vaccination status, the RR of hospitalisation was 0.57 (95%CI 0.44- 0.75) among cases with no or one vaccination, 0.71 (95%CI 0.60-0.86) among two- dose vaccinated, and 0.50 (95%CI 0.32-0.76) among three-dose vaccinated. Interpretation: We found a significantly lower risk of hospitalisation with Omicron infection compared with Delta among both vaccinated and unvaccinated individuals, suggesting an inherent reduced severity of Omicron. Our results can guide modelling of the impact of the ongoing global Omicron wave and thus health care system preparedness.

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DO - 10.2139/ssrn.4008930

M3 - Preprint

BT - Reduced risk of hospitalisation associated with infection with SARS-CoV-2 Omicron relative to Delta

PB - The Lancet Publishing Group

CY - The Lancet Infectious Diseases

ER -

Reduced risk of hospitalisation associated with infection with SARS-CoV-2 Omicron relative to Delta: A Danish cohort study

Abstract

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Carlsberg PandemiX: A Quantitative study of historical and contemporary pandemics

Long-term Impact of Childhood Vaccination Programs: Using Historical data to Understand Modern Disease Patterns

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Reduced risk of hospitalisation associated with infection with SARS-CoV-2 Omicron relative to Delta: A Danish cohort study

Abstract

Link to document

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Carlsberg PandemiX: A Quantitative study of historical and contemporary pandemics

Long-term Impact of Childhood Vaccination Programs: Using Historical data to Understand Modern Disease Patterns

Cite this