The post-pandemic hospital and mortality burden of COVID-19 compared with influenza: A national cohort study in Denmark, May 2022 to June 2024

BackgroundIn the post-pandemic period, COVID-19 continues to cause significant numbers of hospitalisations and deaths. We describe this burden and compare it to the burden of influenza in the first two post-pandemic years in Denmark. MethodsA cohort study including residents in Denmark from May 16, 2022, to June 7, 2024. Data were obtained from national registries, including information on Polymerase chain reaction (PCR) test-positive COVID-19 and influenza admissions, mortality within 30 days of admission, sex, age, COVID-19 and influenza vaccination, comorbidity, and living in long-term care facility for elderly. Negative binomial regression was used to estimate adjusted incidence rate ratios (aIRRs) to compare rates of admissions between COVID-19 and influenza. To assess severity of COVID-19 among hospitalized patients, we used Cox proportional hazard models to estimate adjusted hazard ratios (aHR) of 30-day mortality between COVID-19 and influenza. ResultsAmong 5,899,170 individuals, admissions with COVID-19 (n=24,687) were more frequent than admissions with influenza (n=8,682; aIRR 2.01, 95%CI 1.37-2.95), in particular during the first year (p=0.01), in the summer (p<0.001) and among people above 65 years of age (p<0.001). The number of deaths were also higher (COVID-19, n=2,393; influenza, n=522). Among patients, the risk of mortality of COVID-19 was higher than influenza in the 12-30 days following admission (0-11 days, aHR 1.08, 95%CI 0.94-1.25; 12-30 days, aHR 1.50, 95%CI 1.21-1.84), in particular among non-vaccinated for both COVID-19 and influenza (aHR 1.81, 95%CI 1.25-2.62), while it was similar to influenza among patients without comorbidities (aHR 1.07, 95%CI 0.63-1.80). ConclusionCOVID-19 represented a greater disease burden than influenza, with more hospitalisations and deaths, and more severe disease primarily among non-vaccinated and comorbid patients. These results highlight the continued need for attention and public health efforts to mitigate the impact of SARS-CoV-2.