Acute COVID-19 severity and impaired cognitive function up to 32 months after diagnosis: an observational study

BACKGROUND: Cognitive dysfunction ("brain fog") is a commonly reported post-COVID-19 symptom. Leveraging data from five general population cohorts across four European countries (Estonia, Iceland, Norway, and Sweden), we assessed long-term prevalence of impaired subjective cognitive function among individuals diagnosed with COVID-19 by acute illness severity. METHODS: The included cohorts consisted of adult participants recruited from March 2020 and followed with self-report measures of cognitive function and past COVID-19 infection (except one cohort consisting of clinically confirmed COVID-19 cases) through February 2023. In a cross-sectional analysis we contrasted the prevalence of impaired cognitive function among individuals with and without a COVID-19 diagnosis, overall and by illness severity up to 32 months post-diagnosis. We adjusted for age, gender, education, relationship status, binge drinking, body mass index, previous psychiatric diagnosis, number of chronic medical conditions, and response period. In a longitudinal analysis, we assessed potential changes in cognitive function scores before and after COVID-19 diagnosis. RESULTS: The study population consisted of 153,841 participants (71% women), with 31,359 (20.4%) reporting a positive COVID-19 test. Overall, a COVID-19 diagnosis was not statistically significantly associated with increased prevalence ratio (PR) of impaired cognitive function (PR 1.30 [95% CI: 0.98-1.71]). Individuals bedridden due to COVID-19 for 1-6 days (PR 1.38 [95% CI 0.96-1.99]) or ≥ 7 days (2.59 [1.55-4.33]) had higher prevalence of impaired cognitive function compared to those never diagnosed, while individuals never bedridden had a lower prevalence to those never diagnosed with COVID-19 (0.89 [0.80-1.00]). These findings were corroborated in the longitudinal analysis where a pre- to post diagnosis decline in cognitive function was observed among individuals bedridden due to COVID-19 (p < 0.0001). CONCLUSIONS: The data indicates that a severe COVID-19 acute illness course is associated with impaired cognitive function up to 18-32 months after COVID-19 diagnosis.

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Journal
BMC Medicine
Published
2026-04-11
DOI
https://doi.org/10.1186/s12916-026-04856-2
Primary Topic
Long-Term Effects of COVID-19
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article
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article

Acute COVID-19 severity and impaired cognitive function up to 32 months after diagnosis: an observational study

Kadri Kõiv, John Arne Dahl, Arne Søraas, Elías Eyþórsson et al.
BMC Medicine
Long-Term Effects of COVID-19
article

Acute COVID-19 severity and impaired cognitive function up to 32 months after diagnosis: an observational study

Kadri Kõiv, John Arne Dahl, Arne Søraas, Elías Eyþórsson, UA Valdimarsdottir, Arna Hauksdóttir, Sonja Hjellegjerde Brunvoll, Mette Istre, Karl Trygve Kalleberg, Anna Bára Unnarsdóttir, Mary M. Barker, Kelli Lehto, Anikó Lovik, Sverre Urnes Johnson, Anders Benteson Nygaard, Emma M. Frans, Merete Ellingjord-Dale, Jóhanna Jakobsdóttir, Ingibjörg Magnúsdóttir, Runólfur Pálsson, Hrönn Harðardóttir, Gunnar Tómasson, Reedik Mägi, Thor Aspelund, Edda Bjork Thordardottir, Harpa Rúnarsdóttir, Nils Inge Landrø, Ragnhild Bø, Elísabet U Gísladóttir, Asle Hoffart, Anna K. Kähler, Qing Shen, Omid V. Ebrahimi, Harpa Lind Hjördísar Jónsdóttir, Gillian Murphy, Kristjana Hrönn Ásbjörnsdóttir, Fang Fang
article en

Abstract

BACKGROUND: Cognitive dysfunction ("brain fog") is a commonly reported post-COVID-19 symptom. Leveraging data from five general population cohorts across four European countries (Estonia, Iceland, Norway, and Sweden), we assessed long-term prevalence of impaired subjective cognitive function among individuals diagnosed with COVID-19 by acute illness severity. METHODS: The included cohorts consisted of adult participants recruited from March 2020 and followed with self-report measures of cognitive function and past COVID-19 infection (except one cohort consisting of clinically confirmed COVID-19 cases) through February 2023. In a cross-sectional analysis we contrasted the prevalence of impaired cognitive function among individuals with and without a COVID-19 diagnosis, overall and by illness severity up to 32 months post-diagnosis. We adjusted for age, gender, education, relationship status, binge drinking, body mass index, previous psychiatric diagnosis, number of chronic medical conditions, and response period. In a longitudinal analysis, we assessed potential changes in cognitive function scores before and after COVID-19 diagnosis. RESULTS: The study population consisted of 153,841 participants (71% women), with 31,359 (20.4%) reporting a positive COVID-19 test. Overall, a COVID-19 diagnosis was not statistically significantly associated with increased prevalence ratio (PR) of impaired cognitive function (PR 1.30 [95% CI: 0.98-1.71]). Individuals bedridden due to COVID-19 for 1-6 days (PR 1.38 [95% CI 0.96-1.99]) or ≥ 7 days (2.59 [1.55-4.33]) had higher prevalence of impaired cognitive function compared to those never diagnosed, while individuals never bedridden had a lower prevalence to those never diagnosed with COVID-19 (0.89 [0.80-1.00]). These findings were corroborated in the longitudinal analysis where a pre- to post diagnosis decline in cognitive function was observed among individuals bedridden due to COVID-19 (p < 0.0001). CONCLUSIONS: The data indicates that a severe COVID-19 acute illness course is associated with impaired cognitive function up to 18-32 months after COVID-19 diagnosis.

BMC Medicine
Tongji University (CN), Leiden University (NL), Reykjavík University (IS), Oslo University Hospital (NO), Harvard University (US), University of Iceland (IS), University of Oslo (NO), Karolinska Institutet (SE), University of Oxford (GB), National University Hospital of Iceland (IS), Modum Bad – Gordon Johnsens stiftelse (NO), Icelandic Heart Association (IS), University of Tartu (EE)
Eesti Teadusagentuur, NordForsk, Forskningsrådet om Hälsa, Arbetsliv och Välfärd, Horizon 2020
Openalex Percentile: Top 16%
Long-Term Effects of COVID-19
DOIOpen Access PDFOpenAlex
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