Length of hospital stay and risk of intensive care admission and in-hospital death among COVID-19 patients in Norway: a register-based cohort study comparing patients fully vaccinated with an mRNA vaccine to unvaccinated patients

Abstract

Objectives: We estimated the length of stay (LoS) in hospital and the intensive care unit (ICU) and risk of admission to ICU and in-hospital death among COVID-19 patients ≥18 years in Norway who had been fully vaccinated with an mRNA vaccine (at least two doses or one dose and previous SARS-CoV-2 infection), compared to unvaccinated patients.

Methods: Using national registry data, we analyzed SARS-CoV-2-positive patients hospitalized in Norway between 1 February and 30 November 2021, with COVID-19 as the main cause of hospitalization. We ran Cox proportional hazards models adjusting for vaccination status, age, sex, county of residence, regional health authority, date of admission, country of birth, virus variant, and underlying risk factors.

Results: We included 716 fully vaccinated patients (crude overall median LoS: 5.2 days; admitted to ICU: 103 (14%); in-hospital death: 86 (13%)) and 2487 unvaccinated patients (crude overall median LoS: 5.0 days; admitted to ICU: 480 (19%); in-hospital death: 102 (4%)). In adjusted models, fully vaccinated patients had a shorter overall LoS in hospital (adjusted log hazard ratios (aHR) for discharge: 1.61, 95% CI: 1.24-2.08), shorter LoS without ICU (aHR: 1.27, 95% CI: 1.07-1.52), and lower risk of ICU admission (aHR: 0.50, 95% CI: 0.37-0.69) compared to unvaccinated patients. We observed no difference in the LoS in ICU or in risk of in-hospital death between fully vaccinated and unvaccinated patients.

Discussion: Fully vaccinated patients hospitalized with COVID-19 in Norway have a shorter LoS and lower risk of ICU admission than unvaccinated patients. These findings can support patient management and ongoing capacity planning in hospitals.

Keywords: Breakthrough infection; Hospitalization; Intensive care; Length of stay; Norway; SARS-CoV-2; mRNA vaccine.

Fig. 1

Adjusted hazard ratios for discharge from hospital with and without stay in ICU, ICU admission, discharge from ICU, and in-hospital death from a Cox proportional hazards model for SARS-CoV-2 positive patients aged ≥18 years hospitalized with COVID-19 as the main cause of hospitalization, by age (Norway, 1 February–30 November 2021). The reference group with a hazard ratio = 1 is patients who are male, aged 56 years (median age in dataset), AND without underlying risk factors and unvaccinated. Hazard ratios were calculated using a Cox proportional hazards model. The variables shown in each panel are those significantly associated with each outcome in multivariable models, which were not stratified on (see supplementary materials C). The Akaike information criterion was used to determine whether age was included linearly or with a spline. ICU, intensive care unit.