Reduced risk of hospitalisation among reported COVID-19 cases infected with the SARS-CoV-2 Omicron BA.1 variant compared with the Delta variant, Norway, December 2021 to January 2022

Lamprini Veneti; Håkon Bøås; Anja Bråthen Kristoffersen; Jeanette Stålcrantz; Karoline Bragstad; Olav Hungnes; Margrethe Larsdatter Storm; Nina Aasand; Gunnar Rø; Jostein Starrfelt; Elina Seppälä; Reidar Kvåle; Line Vold; Karin Nygård; Eirik Alnes Buanes; Robert Whittaker

doi:10.2807/1560-7917.ES.2022.27.4.2200077

Reduced risk of hospitalisation among reported COVID-19 cases infected with the SARS-CoV-2 Omicron BA.1 variant compared with the Delta variant, Norway, December 2021 to January 2022

Euro Surveill. 2022 Jan;27(4):2200077. doi: 10.2807/1560-7917.ES.2022.27.4.2200077.

Authors

Lamprini Veneti¹, Håkon Bøås², Anja Bråthen Kristoffersen³, Jeanette Stålcrantz^{2

4}, Karoline Bragstad⁵, Olav Hungnes⁵, Margrethe Larsdatter Storm⁶, Nina Aasand⁶, Gunnar Rø³, Jostein Starrfelt¹, Elina Seppälä², Reidar Kvåle^{7

8}, Line Vold¹, Karin Nygård¹, Eirik Alnes Buanes^{7

9}, Robert Whittaker²

Affiliations

¹ Department of Infection Control and Preparedness, Norwegian Institute of Public Health, Oslo, Norway.
² Department of Infection Control and Vaccines, Norwegian Institute of Public Health, Oslo, Norway.
³ Department of Method Development and Analytics, Norwegian Institute of Public Health, Oslo, Norway.
⁴ European Program for Intervention Epidemiology Training, European Centre for Disease Prevention and Control, Stockholm, Sweden.
⁵ Department of Virology, Norwegian Institute of Public Health, Oslo, Norway.
⁶ Department of Infectious Disease Registries, Norwegian Institute of Public Health, Oslo, Norway.
⁷ Department of Anaesthesia and Intensive Care, Haukeland University Hospital, Bergen, Norway.
⁸ Department of Clinical Medicine, University of Bergen, Bergen, Norway.
⁹ Norwegian Intensive Care and Pandemic Registry, Haukeland University Hospital, Bergen, Norway.

PMID: 35086614
PMCID: PMC8796289
DOI: 10.2807/1560-7917.ES.2022.27.4.2200077

Abstract

We included 39,524 COVID-19 Omicron and 51,481 Delta cases reported in Norway from December 2021 to January 2022. We estimated a 73% reduced risk of hospitalisation (adjusted hazard ratio: 0.27; 95% confidence interval: 0.20-0.36) for Omicron compared with Delta. Compared with unvaccinated groups, Omicron cases who had completed primary two-dose vaccination 7-179 days before diagnosis had a lower reduced risk than Delta (66% vs 93%). People vaccinated with three doses had a similar risk reduction (86% vs 88%).

Keywords: B.1.1.529; COVID-19; Delta; Norway; Omicron; hospitalisation.

MeSH terms

COVID-19*
Hospitalization
Humans
Proportional Hazards Models
SARS-CoV-2

Supplementary concepts

SARS-CoV-2 variants