The hospital and mortality burden of COVID-19 compared with influenza in Denmark: a national observational cohort study, 2022–24

Abstract

Background

The COVID-19 pandemic has been on a downward trend since May, 2022, but it continues to cause substantial numbers of hospital admissions and deaths. We describe this burden in the 2 years since May, 2022, and compare it with the burden of influenza in Denmark.

Methods

This observational cohort study included residents in Denmark from May 16, 2022, to June 7, 2024. Data were obtained from national registries, including admissions with COVID-19 or influenza (ie, having a positive PCR test for either virus from 14 days before and up to 2 days after the hospital admission date), deaths, sex, age, COVID-19 and influenza vaccination status, comorbidities, and residence in long-term care facilities. Negative binomial regression was used to estimate adjusted incidence rate ratios (aIRRs) to compare rates of hospital admissions between COVID-19 and influenza. To compare the severity of COVID-19 versus influenza among patients admitted to hospital, we used the Kaplan–Meier estimator to produce weighted cumulative incidence curves and adjusted risk ratios (aRRs) of mortality at 30 days between COVID-19 and influenza admissions.

Findings

Among 5 899 170 individuals, COVID-19 admissions (n=24 400) were more frequent than influenza admissions (n=8385; aIRR 2·04 [95% CI 1·38–3·02]), particularly during the first year (May, 2022, to May, 2023) versus the second year (May, 2023, to June, 2024; p=0·0096), in the summer versus the winter (p<0·0001), and among people aged 65 years or older versus younger than 65 years (p<0·0001). The number of deaths was also higher for patients with COVID-19 (n=2361) than patients with influenza (n=489, aIRR 3·19 [95% CI 2·24–4·53]). Among patients admitted in the winter (n=19 286), the risk of mortality from COVID-19 was higher than for influenza (aRR 1·23 [95% CI 1·08–1·37]), particularly among those without COVID-19 and influenza vaccination (1·36 [1·05–1·67]), with comorbidities (1·27 [1·11–1·43]), and who were male (1·36 [1·14–1·59]).

Interpretation

COVID-19 represented a greater disease burden than influenza, with more hospital admissions and deaths, and more severe disease (primarily among non-vaccinated people, those with comorbidities, and male patients). These results highlight the continued need for attention and public health efforts to mitigate the impact of SARS-CoV-2.

Funding

Danish Government.