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

• Published in: Euro surveillance : bulletin européen sur les maladies transmissibles Vol. 27; no. 4
• Main Authors: Veneti, Lamprini, Bøås, Håkon, Bråthen Kristoffersen, Anja, Stålcrantz, Jeanette, Bragstad, Karoline, Hungnes, Olav, Storm, Margrethe Larsdatter, Aasand, Nina, Rø, Gunnar, Starrfelt, Jostein, Seppälä, Elina, Kvåle, Reidar, Vold, Line, Nygård, Karin, Buanes, Eirik Alnes, Whittaker, Robert
• Format: Journal Article
• Language: English
• Published: Sweden Centre Europeen pour la Surveillance Epidemiologique du SIDA (European Centre for the Epidemiological Monitoring of AIDS) 27-01-2022; European Centre for Disease Prevention and Control (ECDC)
• Subjects: COVID-19; Disease prevention; Hospitalization; Humans; Pandemics; Proportional Hazards Models; Rapid Communication; Risk factors; SARS-CoV-2; Severe acute respiratory syndrome coronavirus 2; Norway; COVID-19; Omicron; B.1.1.529; Delta; Norway; hospitalisation
• ISSN: 1560-7917; 1025-496X; 1560-7917
• DOI: 10.2807/1560-7917.ES.2022.27.4.2200077

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%).