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Post-infection sequelae of COVID-19 and other infectious diseases—a nationwide Danish study with 40-month follow-up
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  • Published: 13 March 2026

Post-infection sequelae of COVID-19 and other infectious diseases—a nationwide Danish study with 40-month follow-up

  • Clara S. Grønkjær  ORCID: orcid.org/0000-0001-7739-19171,
  • Rune Haubo B. Christensen  ORCID: orcid.org/0000-0002-4494-33991,
  • Daniel Kondziella  ORCID: orcid.org/0000-0001-5562-98082,3 na1 &
  • …
  • Michael E. Benros  ORCID: orcid.org/0000-0003-4939-94651,3 na1 

Nature Communications , Article number:  (2026) Cite this article

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Subjects

  • Cardiovascular diseases
  • Neurological disorders
  • Psychiatric disorders
  • Respiratory tract diseases
  • Viral infection

Abstract

Nationwide follow-up studies of long-term post-acute COVID-19 sequelae compared with sequelae of other infections have been lacking. Using nationwide registers, we analyzed all SARS-CoV-2 PCR test results, prescriptions for anti-infective agents, and hospitalizations with COVID-19 or other infections in Denmark from March 2020 to June 2023, including up to 40-month follow-up. We used Cox proportional hazards models with time-varying exposures to estimate the rates of first-time mental disorders (n = 5,306,132) and general medical conditions (n = 3,517,630). Here we show that positive SARS-CoV-2 PCR tests alone were not associated with clinically relevant increased rates of mental disorders or general medical conditions when compared with negative SARS-CoV-2 PCR tests, nor when compared to individuals with anti-infective prescriptions. Rates of general medical conditions after a positive compared with a negative SARS-CoV-2 PCR test were only elevated for virus types preceding Omicron and for individuals with less than 3 vaccination doses. Compared with the general population, the rates of mental disorders or general medical conditions were elevated among hospitalized COVID-19 patients, and particularly when ICU treatment was required. However, when comparing patients hospitalized with COVID-19 to patients hospitalized with non-COVID-19 pulmonary infections or other infections, the rates of mental disorders or general medical conditions were increased to the same extent. In conclusion, severe COVID-19 post-infection sequelae are comparable to sequelae observed after other infections of similar severity.

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Data availability

We used the following registers: the Microbiology Database, the Danish National Patient Register, the Danish Psychiatric Central Research Register, the Population Education Register, the Income Statistics Register, and the Danish National Prescription Register. The data are available from Statistics Denmark, https://www.dst.dk/en/TilSalg/Forskningsservice/Dataadgang. To access health data in Denmark, applications must be submitted to the Danish Data Protection Agency, the Danish National Board of Health, and Statistics Denmark. For more information, see https://www.itgovernance.eu/da-dk/eu-gdpr-compliance-dk, https://sundhedsdatastyrelsen.dk/da/english, and https://dst.dk/en. Source data are provided with this paper.

Code availability

Code available at: https://github.com/Biological-and-Precision-Psychiatry/COVID-19-post-infection-sequelae63. The managing of data, analyses, and illustrations were made in R version 4.4.1. Analyses using the Cox proportional hazards model were performed with the coxph function from the survival package version 3.7-0. Additional packages used (version): data.table (1.16.2), dplyr (1.1.4), lubridate (1.9.3), foreach (1.5.2), doParallel (1.0.17), and emmeans (1.10.2).

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Acknowledgements

We thank Elisabeth Anne Wreford Andersen for invaluable input for the pre-registration of this study and the data analysis. The research was funded by an unrestricted grant from the Novo Nordisk Foundation (grant number NNF21OC0067769) (M.E.B. and D.K.) and the Lundbeck Foundation (grant number 349-2020-658) (M.E.B. and D.K.). The funding sources had no role in the design, data, analysis, interpretation, writing of the article, or decision to publish the findings.

Author information

Author notes

  1. These authors jointly supervised this work: Daniel Kondziella, Michael E. Benros.

Authors and Affiliations

  1. Copenhagen Research Centre for Biological and Precision Psychiatry, Mental Health Centre Copenhagen, Copenhagen University Hospital, Copenhagen, Denmark

    Clara S. Grønkjær, Rune Haubo B. Christensen & Michael E. Benros

  2. Departments of Neurology, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark

    Daniel Kondziella

  3. Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark

    Daniel Kondziella & Michael E. Benros

Authors
  1. Clara S. Grønkjær
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  2. Rune Haubo B. Christensen
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Contributions

M.E.B. and D.K. received funding for the study. All authors participated in the design of the study. C.S.G. and R.H.B.C. verified the underlying data. C.S.G. conducted the statistical analysis, wrote the first draft of the manuscript, and all authors contributed to editing and approving the final version.

Corresponding authors

Correspondence to Daniel Kondziella or Michael E. Benros.

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Grønkjær, C.S., Christensen, R.H.B., Kondziella, D. et al. Post-infection sequelae of COVID-19 and other infectious diseases—a nationwide Danish study with 40-month follow-up. Nat Commun (2026). https://doi.org/10.1038/s41467-026-70351-0

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  • Received: 30 December 2024

  • Accepted: 25 February 2026

  • Published: 13 March 2026

  • DOI: https://doi.org/10.1038/s41467-026-70351-0

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