ABSTRACT
BACKGROUND: Waves of infection have formed the pattern of the COVID-19 pandemic. A wave dominated by the delta variant of the SARS-CoV-2 virus in autumn 2021 was superseded by the omicron variant over the course of a few weeks around Christmas. We describe how this transition affected the population of patients admitted to a Norwegian local hospital with COVID-19. MATERIAL AND METHOD: All patients admitted to Bærum Hospital with confirmed SARS-CoV-2 virus were included in a quality study which aimed to describe patient characteristics and clinical course. We present patients admitted in the periods 28 June 2021-31 December 2021 and 1 January 2022-12 June 2022, described here as the delta wave and the omicron wave. RESULTS: The SARS-CoV-2-virus was confirmed in a total of 144 patients who were admitted during the delta wave, and in 261 patients during the omicron wave, where 14/144 (10 %) and 89/261 (34 %) were admitted for reasons other than COVID-19. Patients with COVID-19 during the delta wave were younger on average (59 vs. 69 years) and had a lower Charlson comorbidity index score (2.6 vs. 4.9) and a lower Clinical Frailty Scale score (2.8 vs. 3.7) than patients in the omicron wave. Among 302/405 patients admitted with COVID-19 as the principal diagnosis, 88/130 (68 %) patients had respiratory failure during the delta wave and 59/172 (34 %) during the omicron wave, with a median number of 8 bed days (interquartile range 5-15) and 5 (interquartile range 3-8). INTERPRETATION: The transition from the wave of infection that was dominated by the delta variant of the SARS-CoV-2 virus to the wave dominated by the omicron variant had a considerable effect on the characteristics and clinical course of patients admitted to hospital with SARS-CoV-2 infection.