News -- Publication on acute COVID-19 severity and long-term cognitive function

News

I am pleased to share our new study published in BMC Medicine, pooling data from five general-population cohorts across Estonia, Iceland, Norway and Sweden (n = 153,841, of whom 20.4% had a confirmed SARS-CoV-2 infection) to ask whether persistent cognitive complaints after COVID-19 track with the severity of the acute illness.

The headline finding is that a COVID-19 diagnosis on its own was not strongly associated with self-reported cognitive impairment — but acute severity was. Participants who had been bedridden for seven days or more during the acute phase had a prevalence ratio of 2.59 (95% CI 1.55–4.33) for impaired cognitive function compared with never-infected controls, with a smaller elevation among those bedridden 1–6 days. Longitudinal within-person analyses confirmed a pre- to post-infection decline in cognitive function among the infected, up to 32 months after diagnosis.

These results add to a growing body of work — including our previous studies from the Norwegian COVID-19 Cohort — suggesting that the cognitive sequelae of COVID-19 are real, persistent, and concentrated among those with more severe acute illness.

The paper is published in BMC Medicine.

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 with 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.