The post-pandemic hospital and mortality burden of COVID-19 compared with influenza: A national cohort study in Denmark, May 2022 to June 2024
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Background
In 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.
Methods
A 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.
Results
Among 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).
Conclusion
COVID-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.
