Risk of hospitalisation associated with infection with SARS-CoV-2 omicron variant versus delta variant in Denmark: an observational cohort study

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

doi:10.1016/S1473-3099(22)00154-2

Risk of hospitalisation associated with infection with SARS-CoV-2 omicron variant versus delta variant in Denmark: an observational cohort study

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

^*Corresponding author for this work

Research output: Contribution to journal › Journal article › Research › peer-review

2 Citations (Scopus)

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.

Original language	English
Journal	The Lancet Infectious Diseases
Volume	22
Issue number	7
Pages (from-to)	967-976
Number of pages	10
ISSN	1473-3099
DOIs	https://doi.org/10.1016/S1473-3099(22)00154-2
Publication status	Published - 2022

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Publisher Copyright:
© 2022 Elsevier Ltd

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10.1016/S1473-3099(22)00154-2

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9033212/pdf/main.pdf

Cite this

Bager, P., Wohlfahrt, J., Bhatt, S., Stegger, M., Legarth, R., Møller, C. H., Skov, R. L., Valentiner-Branth, P., Voldstedlund, M., Fischer, T. K., Simonsen, L., Kirkby, N. S., Thomsen, M. K., Spiess, K., Marving, E., Larsen, N. B., Lillebaek, T., Ullum, H., Mølbak, K., ... the Omicron-Delta study group (2022). Risk of hospitalisation associated with infection with SARS-CoV-2 omicron variant versus delta variant in Denmark: an observational cohort study. The Lancet Infectious Diseases, 22(7), 967-976. https://doi.org/10.1016/S1473-3099(22)00154-2

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; Edslev, Sofie Marie; Sieber, Raphael Niklaus; Ingham, Anna Cäcilia; Overvad, Maria; Agermose Gram, Mie; Kristensen Lomholt, Frederikke; Hallundbæk, Louise; Hjorth Espensen, Caroline; Gubbels, Sophie; Karakis, Marianne; Lauenborg Møller, Karina; Schytte Olsen, Stefan; Harboe, Zitta Barrella; Klint Johannesen, Caroline; van Wijhe, Maarten; Holler, Jon Gitz; Dessau, Ram Benny Christian; Barfred Friis, Martin; Fuglsang-Damgaard, David; Pinholt, Mette; Vognbjerg Sydenham, Thomas; Coia, John Eugenio; Marmolin, Ea Sofie; Fomsgaard, Anders; Fonager, Jannik; Rasmussen, Morten; Cohen, Arieh; the Omicron-Delta study group.

In: The Lancet Infectious Diseases, Vol. 22, No. 7, 2022, p. 967-976.

Research output: Contribution to journal › Journal article › Research › peer-review

Bager, P, Wohlfahrt, J, Bhatt, S, Stegger, M, Legarth, R, Møller, CH, Skov, RL, Valentiner-Branth, P, Voldstedlund, M, Fischer, TK, Simonsen, L, Kirkby, NS, Thomsen, MK, Spiess, K, Marving, E, Larsen, NB, Lillebaek, T, Ullum, H, Mølbak, K, Krause, TG, Edslev, SM, Sieber, RN, Ingham, AC, Overvad, M, Agermose Gram, M, Kristensen Lomholt, F, Hallundbæk, L, Hjorth Espensen, C, Gubbels, S, Karakis, M, Lauenborg Møller, K, Schytte Olsen, S, Harboe, ZB, Klint Johannesen, C, van Wijhe, M, Holler, JG, Dessau, RBC, Barfred Friis, M, Fuglsang-Damgaard, D, Pinholt, M, Vognbjerg Sydenham, T, Coia, JE, Marmolin, ES, Fomsgaard, A, Fonager, J, Rasmussen, M, Cohen, A & the Omicron-Delta study group 2022, 'Risk of hospitalisation associated with infection with SARS-CoV-2 omicron variant versus delta variant in Denmark: an observational cohort study', The Lancet Infectious Diseases, vol. 22, no. 7, pp. 967-976. https://doi.org/10.1016/S1473-3099(22)00154-2

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 ; Edslev, Sofie Marie ; Sieber, Raphael Niklaus ; Ingham, Anna Cäcilia ; Overvad, Maria ; Agermose Gram, Mie ; Kristensen Lomholt, Frederikke ; Hallundbæk, Louise ; Hjorth Espensen, Caroline ; Gubbels, Sophie ; Karakis, Marianne ; Lauenborg Møller, Karina ; Schytte Olsen, Stefan ; Harboe, Zitta Barrella ; Klint Johannesen, Caroline ; van Wijhe, Maarten ; Holler, Jon Gitz ; Dessau, Ram Benny Christian ; Barfred Friis, Martin ; Fuglsang-Damgaard, David ; Pinholt, Mette ; Vognbjerg Sydenham, Thomas ; Coia, John Eugenio ; Marmolin, Ea Sofie ; Fomsgaard, Anders ; Fonager, Jannik ; Rasmussen, Morten ; Cohen, Arieh ; the Omicron-Delta study group. / Risk of hospitalisation associated with infection with SARS-CoV-2 omicron variant versus delta variant in Denmark : an observational cohort study. In: The Lancet Infectious Diseases. 2022 ; Vol. 22, No. 7. pp. 967-976.

@article{19e074a053c94239bc759934607563bb,

title = "Risk of hospitalisation associated with infection with SARS-CoV-2 omicron variant versus delta variant in Denmark: an observational cohort study",

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.",

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

note = "Publisher Copyright: {\textcopyright} 2022 Elsevier Ltd",

year = "2022",

doi = "10.1016/S1473-3099(22)00154-2",

language = "English",

volume = "22",

pages = "967--976",

journal = "The Lancet Infectious Diseases",

issn = "1473-3099",

publisher = "TheLancet Publishing Group",

number = "7",

}

TY - JOUR

T1 - Risk of hospitalisation associated with infection with SARS-CoV-2 omicron variant versus delta variant in Denmark

T2 - an observational cohort study

AU - Bager, Peter

AU - Wohlfahrt, Jan

AU - Bhatt, Samir

AU - Stegger, Marc

AU - Legarth, Rebecca

AU - Møller, Camilla Holten

AU - Skov, Robert Leo

AU - Valentiner-Branth, Palle

AU - Voldstedlund, Marianne

AU - Fischer, Thea K.

AU - Simonsen, Lone

AU - Kirkby, Nikolai Søren

AU - Thomsen, Marianne Kragh

AU - Spiess, Katja

AU - Marving, Ellinor

AU - Larsen, Nicolai Balle

AU - Lillebaek, Troels

AU - Ullum, Henrik

AU - Mølbak, Kåre

AU - Krause, Tyra Grove

AU - Edslev, Sofie Marie

AU - Sieber, Raphael Niklaus

AU - Ingham, Anna Cäcilia

AU - Overvad, Maria

AU - Agermose Gram, Mie

AU - Kristensen Lomholt, Frederikke

AU - Hallundbæk, Louise

AU - Hjorth Espensen, Caroline

AU - Gubbels, Sophie

AU - Karakis, Marianne

AU - Lauenborg Møller, Karina

AU - Schytte Olsen, Stefan

AU - Harboe, Zitta Barrella

AU - Klint Johannesen, Caroline

AU - van Wijhe, Maarten

AU - Holler, Jon Gitz

AU - Dessau, Ram Benny Christian

AU - Barfred Friis, Martin

AU - Fuglsang-Damgaard, David

AU - Pinholt, Mette

AU - Vognbjerg Sydenham, Thomas

AU - Coia, John Eugenio

AU - Marmolin, Ea Sofie

AU - Fomsgaard, Anders

AU - Fonager, Jannik

AU - Rasmussen, Morten

AU - Cohen, Arieh

AU - the Omicron-Delta study group

PY - 2022

Y1 - 2022

N2 - 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.

AB - 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.

U2 - 10.1016/S1473-3099(22)00154-2

DO - 10.1016/S1473-3099(22)00154-2

M3 - Journal article

C2 - 35468331

AN - SCOPUS:85132538661

VL - 22

SP - 967

EP - 976

JO - The Lancet Infectious Diseases

JF - The Lancet Infectious Diseases

SN - 1473-3099

IS - 7

ER -