Milder disease trajectory among COVID-19 patients hospitalised with the SARS-CoV-2 Omicron variant compared with the Delta variant in Norway

Abstract

Using individual-level national registry data, we conducted a cohort study to estimate differences in the length of hospital stay, and risk of admission to an intensive care unit and in-hospital death among patients infected with the SARS-CoV-2 Omicron variant, compared to patients infected with Delta variant in Norway. We included 409 (38%) patients infected with Omicron and 666 (62%) infected with Delta who were hospitalised with COVID-19 as the main cause of hospitalisation between 6 December 2021 and 6 February 2022. Omicron patients had a 48% lower risk of intensive care admission (aHR: 0.52, 95%CI: 0.34-0.80) and a 56% lower risk of in-hospital death (aHR: 0.44, 95%CI: 0.24-0.79) compared to Delta patients. Omicron patients had a shorter length of stay (with or without ICU stay) compared to Delta patients in the age groups from 18-79 years and those who had at least completed their primary vaccination. This supports growing evidence of reduced disease severity among hospitalised Omicron patients compared with Delta patients.

Differences between the course of SARS-CoV-2 infections in the periods of the Delta and Omicron variants dominance in Poland

“…Consistent with the more severe baseline clinical status of patients infected with the Delta variant, patients presented higher levels of inflammatory parameters such as CRP and IL-6, and this trend was supported by other studies [36,37]. Although CRP level and IL-6 concentration were lower in patients hospitalized during Omicron period, total leukocyte count was higher.…”

The surveillance of patients hospitalised with COVID-19 in Norway: a comparison of two register-based systems

“…The decreasing overlap between the registries from late-2021 coincided with the Delta variant being superseded by the milder Omicron variant [7,27], increasing vaccination coverage [24] as well as the gradual scaling back of non-pharmaceutical interventions and testing in Norway. This consequently impacted the flow to, and management of, COVID-19 positive patients in hospital, with patients becoming gradually more spread out across hospitals, instead of being treated in specific wards usually under the care of infectious disease physicians.…”

“…It is also more challenging to distinguish patients hospitalised with and due to COVID-19. Furthermore, the timeliness of a system based on discharge codes is intrinsically linked to length of stay, which may vary over time [27,36].…”