Key Points
Question
How are post–COVID-19 condition self-reported cognitive symptoms associated with employment status, functional outcomes, and mood?
Findings
In this survey study including 14 767 individuals with post–COVID-19 condition surveyed in late 2022 to early 2023, 57% reported experiencing cognitive symptoms daily, compared with 27% with prior SARS-CoV-2 infection who did not develop post–COVID-19 condition. In those with post–COVID-19 condition, cognitive symptoms were associated with greater levels of depressive symptoms, greater reported functional impairment, and lesser likelihood of full-time employment.
Meaning
The findings of this study suggest that self-reported cognitive symptoms are prevalent in post–COVID-19 condition, often co-occur with depressive symptoms, and are associated with functional impairment.
Abstract
Importance
The frequent occurrence of cognitive symptoms in post–COVID-19 condition has been described, but the nature of these symptoms and their demographic and functional factors are not well characterized in generalizable populations.
Objective
To investigate the prevalence of self-reported cognitive symptoms in post–COVID-19 condition, in comparison with individuals with prior acute SARS-CoV-2 infection who did not develop post–COVID-19 condition, and their association with other individual features, including depressive symptoms and functional status.
Design, Setting, and Participants
Two waves of a 50-state nonprobability population-based internet survey conducted between December 22, 2022, and May 5, 2023. Participants included survey respondents aged 18 years and older.
Exposure
Post–COVID-19 condition, defined as self-report of symptoms attributed to COVID-19 beyond 2 months after the initial month of illness.
Main Outcomes and Measures
Seven items from the Neuro-QoL cognition battery assessing the frequency of cognitive symptoms in the past week and patient Health Questionnaire-9.
Results
The 14 767 individuals reporting test-confirmed COVID-19 illness at least 2 months before the survey had a mean (SD) age of 44.6 (16.3) years; 568 (3.8%) were Asian, 1484 (10.0%) were Black, 1408 (9.5%) were Hispanic, and 10 811 (73.2%) were White. A total of 10 037 respondents (68.0%) were women and 4730 (32.0%) were men. Of the 1683 individuals reporting post–COVID-19 condition, 955 (56.7%) reported at least 1 cognitive symptom experienced daily, compared with 3552 of 13 084 (27.1%) of those who did not report post–COVID-19 condition. More daily cognitive symptoms were associated with a greater likelihood of reporting at least moderate interference with functioning (unadjusted odds ratio [OR], 1.31 [95% CI, 1.25-1.36]; adjusted [AOR], 1.30 [95% CI, 1.25-1.36]), lesser likelihood of full-time employment (unadjusted OR, 0.95 [95% CI, 0.91-0.99]; AOR, 0.92 [95% CI, 0.88-0.96]) and greater severity of depressive symptoms (unadjusted coefficient, 1.40 [95% CI, 1.29-1.51]; adjusted coefficient 1.27 [95% CI, 1.17-1.38). After including depressive symptoms in regression models, associations were also found between cognitive symptoms and at least moderate interference with everyday functioning (AOR, 1.27 [95% CI, 1.21-1.33]) and between cognitive symptoms and lower odds of full-time employment (AOR, 0.92 [95% CI, 0.88-0.97]).
Conclusions and Relevance
The findings of this survey study of US adults suggest that cognitive symptoms are common among individuals with post–COVID-19 condition and associated with greater self-reported functional impairment, lesser likelihood of full-time employment, and greater depressive symptom severity. Screening for and addressing cognitive symptoms is an important component of the public health response to post–COVID-19 condition.
This survey study examines self-reported cognitive symptoms of post–COVID-19 syndrome and the association of these symptoms with individuals' employment status, functional outcomes, and mood.
Introduction
Persistence or late emergence of symptoms after acute infection with the SARS-CoV-2 virus, often referred to as long COVID1 or post-acute COVID-19 syndrome,2 is common. While estimates of the prevalence of post–COVID-19 condition vary widely depending on definition, methods, and sampling frame, studies suggest that at least 10% of individuals will experience at least some of these symptoms,3,4,5 including cognitive difficulties, fatigue, and mood changes.
Developing effective public health strategies for post–COVID-19 condition requires better understanding of the symptoms that compose this syndrome, their prevalence, and their association with functional outcomes.2,6 The recognition that the sequelae of COVID-19 represent a persistent public health crisis prompted a National Academy of Medicine effort to refine post–COVID-19 condition definitions and substantial investment from the US government to understand mechanisms and develop treatments for post–COVID-19 condition through the National Institutes of Health RECOVER initiative.7
In early work, cognitive deficits were reported to be common after acute COVID-19 illness.8 Subsequent work confirmed the persistence of deficits in attention, speed of information processing, executive functions, and memory.9,10,11,12,13 As recognition of post–COVID-19 condition as a syndrome emerged, cognition was initially investigated in small convenience samples of patients seeking care at single or multiple COVID-19–related specialty clinics,12,14,15 which may limit generalizability because of selection bias. Most larger studies have used International Classification of Diseases codes from electronic health records and health claims data,3,13,16 but individual signs or symptoms may not be captured reliably in encounter diagnostic codes.3 One exception is a large study in 2020 using a web-based platform17 that included 12 689 individuals in the UK with a suspected history of COVID-19 acute infection. That study identified cognitive deficits in multiple domains that were associated with the severity of COVID-19 acute infection but also observed persistence of cognitive weaknesses during the post–COVID-19 condition phase.
Beyond the individual cognitive symptoms of post–COVID-19 condition, their association with functioning has not been well established. Post–COVID-19 condition in general often compromises quality of life18 and has been associated with occupational difficulties19 and diminished everyday activities of daily living.20 A study of 3754 adults treated at a COVID-19 follow-up clinic from 2020 to March 2022 reported an association between self-reported cognitive symptoms and occupational and social function.21 Similarly, analysis of a cohort of patients seeking care at a COVID-19 clinic in 2020-2021 found that executive dysfunction demonstrated an association with work impairment and work absenteeism.22 Most recently, an association between self-reported cognitive impairment and unemployment in a survey-based design was reported.23 Still, the extent to which findings from early in the pandemic remain applicable to later infections is unknown, particularly as the risk of cognitive symptoms after COVID-19 may not have been stable through the course of the pandemic.13,24,25
To better understand the nature and correlates of cognitive symptoms in post–COVID-19 condition, we applied data from 2 waves of a 50-state US survey to characterize these symptoms among individuals who describe post–COVID-19 condition in comparison with those who report full recovery from SARS-CoV-2 infection. Data were collected from 14 767 individuals between December 22, 2022, and May 5, 2023, as part of a survey that contains questions on a broad array of topics, not solely COVID-19, to mitigate at least in part selection bias. We examined the association of these symptoms with individual respondent characteristics and then sought to evaluate the association between cognitive symptoms and mood and functional status.
Methods
Study Design
We incorporated data from 2 waves of the COVID States Project, an internet survey conducted by a consortium of academic sites (COVIDstates.org)26 between December 22, 2022, and January 7, 2023, and again April 5 to May 5, 2023, in all 50 US states and the District of Columbia. The survey enrolled individuals aged 18 years and older residing in the US, applying nonprobability sampling27 along with state-level representative quotas intended to balance the sample on age, gender, and race and ethnicity. Participants opted in via a commercial panel aggregator (Pure Spectrum) to participate in a general opinion survey; as the survey contained a broad range of questions, it was not promoted as a COVID survey per se. These individuals provided written online consent before accessing the survey, considered to be exempt by the Harvard University Institutional Review Board. All results are described in accordance with the American Association for Public Opinion Research (AAPOR) reporting guideline.28 As an opt-in survey, participation rates are not available.
Measures
Cognitive Symptoms
Questions pertaining to cognitive symptoms were drawn from the Neuro-QoL v2.0 Cognitive Function item bank,29 a psychometrically validated patient-reported outcome measure30 that has been used in individuals recovering from COVID-19.31 Survey respondents were asked to rate on a 5-point Likert-type scale how often they experienced each of the following over the 7 previous days: slowed thinking, trouble concentrating, having to work hard to pay attention to avoid making mistakes, trouble getting started, trouble remembering (eg, taking medicine or buying something), difficulty multitasking, and trouble making decisions. By convention, lower scores on each item correspond to greater cognitive symptom frequency/burden as follows: 5, never; 4, rarely; 3, sometimes (2-3 times in the past 7 days); 2, often (once a day); and 1, very often (several times a day). For purposes of primary analysis, we counted a symptom as present if it was reported as occurring at least daily (ie, score of 2 or 1) and calculated the number of symptoms reported for each respondent. The Neuro-QOL does not ask whether symptoms are new or chronic, only whether they are present.
Mood
We used the 9-item Patient Health Questionnaire (PHQ-9) to screen for depressive symptom severity. The PHQ-9 has strong diagnostic accuracy in assessing depression.32,33 The PHQ-9 consists of 9 items that correspond to the 9 diagnostic criteria of the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition diagnosis of major depressive disorder. Respondents are asked to rate each item on a 0 to 3 Likert-type scale how frequently they experienced each symptom over the past 2 weeks (0, not at all; 3, nearly every day). Scores are summed to yield a total score.
Functional Outcomes
Survey respondents were asked about the extent to which post–COVID-19 condition symptoms interfered in daily life, with options including not at all, a little bit, moderately, quite a bit, and extremely; for analysis, this variable was dichotomized a priori to reflect moderate or greater, or less than moderately. Respondents were also asked about their current employment status, selecting from among working full-time, gig/contract work, homemaker, parttime work, retired, self-employed, student, or unemployed. For consistency with prior work23 and ease of interpretation, we used working full-time (yes vs all others) as a dichotomous variable in logistic regression analyses.
Sociodemographic Variables
Sociodemographic variables were collected by self-report. Race and ethnicity were drawn from US Census categories to confirm representativeness of the US population; we report these categories as specified in a recent guidance statement.34 Survey respondents were asked to identify race and ethnicity from a list including African American or Black, Asian American, Hispanic, Native American, Pacific Islander, White, or Other, and had the opportunity to provide a free-text self-description. For analytic purposes, because of small cell sizes, Native American, Pacific Islander, and Other were collapsed into a single category for analysis.
Post–COVID-19 condition and SARS-CoV-2 infection were defined based on participant self-report. Respondents were first asked whether they had received any positive COVID-19 test result and in what month they received this result. Those who answered affirmatively were further asked whether their symptoms had resolved. Among those indicating that symptoms had not resolved, they were asked to complete a checklist reflecting current acute and post–COVID-19 condition signs and symptoms.25 For consistency with prior work, we defined post–COVID-19 condition among individuals whose survey start date was more than 2 months after the month in which they initially identified a positive COVID-19 test and who continued to report symptoms at the time of the survey. This approximates the 2-month persistence criterion of the World Health Organization35 definition of post–COVID-19 condition, but not the 3-month interval from initial infection. Earlier work reported that alternate definitions relying on self-reported diagnosis rather than positive test results yielded similar results in terms of correlates and outcomes.23
Statistical Analysis
All analyses were conducted using R, version 4.0 (R Foundation for Statistical Computing).36 Descriptive statistics were calculated using the mean (SD) for continuous measures and proportions for categorical variables. We graphically compared the mean score (representing frequency) on each Neuro-QoL item, and the total number of cognitive symptoms reported between those who met criteria for post–COVID-19 condition vs those who did not. Unadjusted odds ratios (ORs) and adjusted ORs (AORs) for presence of cognitive symptoms, for moderate or greater impact of symptoms on daily functioning, and for working full-time were estimated using multiple logistic regression, with adjusted models including sociodemographic features. Pearson correlations between test scores were determined. Linear regression was used to examine sociodemographic features for association with the overall number of symptoms reported. In all regression models, we considered the following features: age in years, gender, educational level (graduate, undergraduate, some college, high school graduate, and some high school or less), annual household income (<$25 000, $25 000-<$50 000, $50 000-<$100 000, and ≥$100 000), race and ethnicity, and rural, suburban, or urban setting. Survey weights were not applied as this represented a nonrandom subset of the larger sample, such that the aim was not to estimate US population rates but rather to derive a cohort of individuals with post–COVID-19 condition based on this larger sample. For participants who responded to more than 1 survey wave, the most recent survey was included; in prior work,37 alternative approaches (ie, using index wave or a random wave, or including multiple within-subject measures and accounting for nested observations) yielded essentially identical results. In light of very low rates of missing data (Table 1), we did not apply multiple imputation. The threshold for statistical significance was considered to be 2-sided P < .05.
Table 1. Characteristics of Individuals Who Did or Did Not Report Persistence of Post–COVID-19 Condition Symptoms for at Least 2 Months.
| Characteristic | No. (%) | P value | ||
|---|---|---|---|---|
| Recovered (n = 13 084) | Post–COVID-19 condition (n = 1683) | Total (N = 14 767) | ||
| Respondent age, mean (SD), y | 44.3 (16.5) | 46.9 (14.9) | 44.6 (16.3) | <.001 |
| Gender | ||||
| Female | 8704 (66.5) | 1333 (79.2) | 10 037 (68.0) | <.001 |
| Male | 4380 (33.5) | 350 (20.8) | 4730 (32.0) | |
| Race and ethnicity | ||||
| African American or Black | 1355 (10.4) | 129 (7.7) | 1484 (10.0) | <.001 |
| Asian American | 540 (4.1) | 28 (1.7) | 568 (3.8) | |
| Hispanic | 1253 (9.6) | 155 (9.2) | 1408 (9.5) | |
| Native American | 126 (1.0) | 18 (1.1) | 144 (1.0) | |
| Othera | 160 (1.2) | 32 (1.9) | 192 (1.3) | |
| Pacific Islander | 132 (1.0) | 28 (1.7) | 160 (1.1) | |
| White | 9518 (72.7) | 1293 (76.8) | 10 811 (73.2) | |
| Education | ||||
| Some high school | 338 (2.6) | 58 (3.4) | 396 (2.7) | <.001 |
| High school degree | 2606 (19.9) | 358 (21.3) | 2964 (20.1) | |
| Some college | 3155 (24.1) | 525 (31.2) | 3680 (24.9) | |
| College degree | 5214 (39.9) | 557 (33.1) | 5771 (39.1) | |
| Graduate degree | 1771 (13.5) | 185 (11.0) | 1956 (13.2) | |
| Employment | ||||
| Full-time | 6275 (48.0) | 669 (39.8) | 6944 (47.0) | <.001 |
| Gig/contract | 54 (0.4) | 10 (0.6) | 64 (0.4) | |
| Homemaker | 830 (6.3) | 127 (7.5) | 957 (6.5) | |
| Parttime | 1362 (10.4) | 173 (10.3) | 1535 (10.4) | |
| Retired | 2143 (16.4) | 319 (19.0) | 2462 (16.7) | |
| Self-employed | 747 (5.7) | 128 (7.6) | 875 (5.9) | |
| Student | 590 (4.5) | 46 (2.7) | 636 (4.3) | |
| Unemployed | 1083 (8.3) | 211 (12.5) | 1294 (8.8) | |
| Income, $ | ||||
| Missing | 5 | 1 | 6 | <.001 |
| <25 000 | 2135 (16.3) | 354 (21.0) | 2489 (16.9) | |
| 25 000 to < 50 000 | 3128 (23.9) | 485 (28.8) | 3613 (24.5) | |
| 50 000 to <100 000 | 4588 (35.1) | 572 (34.0) | 5160 (35.0) | |
| ≥100 000 | 3228 (24.7) | 271 (16.1) | 3499 (23.7) | |
| Urbanicity | ||||
| Rural | 2191 (16.7) | 397 (23.6) | 2588 (17.5) | <.001 |
| Suburban | 7650 (58.5) | 959 (57.0) | 8609 (58.3) | |
| Urban | 3243 (24.8) | 327 (19.4) | 3570 (24.2) | |
| PHQ-9 total score | ||||
| Not administered | 246 | 29 | 275 | <.001 |
| Mean (SD) | 6.2 (6.3) | 9.5 (7.0) | 6.6 (6.5) | |
| Daily cognitive symptoms, mean (SD) | 0.8 (1.7) | 2.3 (2.6) | 1.0 (1.9) | <.001 |
| At least 1 cognitive symptom | 3552 (27.1) | 955 (56.7) | 4507 (30.5) | <.001 |
Abbreviation: PHQ-9, 9-item Patient Health Questionnaire.
Individuals who did not select one of the other categories listed for race and ethnicity could instead indicate Other and respond using free text.
Results
Among all 14 767 individuals reporting test-confirmed SARS-CoV-2 infection at least 2 months before the survey (Table 1), mean (SD) age was 44.6 (16.3) years; 568 (3.8%) were Asian, 1484 (10.0%) were Black, 1408 (9.5%) were Hispanic, and 10 811 (73.2%) were White. A total of 10 037 respondents 68.0%) were women and 4730 (32.0%) were men. A total of 1683 individuals (11.4%) of the full sample met our definition of post–COVID-19 condition. Of the 1683 individuals reporting post–COVID-19 condition, 955 (56.7%) reported at least 1 cognitive symptom experienced daily, compared with 3552 of 13 084 (27.1%) of those who did not report post–COVID-19 condition.
All individual cognitive symptoms were more often reported as occurring at least daily among respondents with post–COVID-19 condition (Figure 1), ranging from trouble with decision-making (25.3%) to trouble concentrating (38.1%), and occurred more frequently overall (eFigure 1 in Supplement 1). Those with post–COVID-19 condition reported, on average, significantly more cognitive symptoms experienced at least daily than those without post–COVID-19 condition (eFigure 2 in Supplement 1).
Figure 1. Proportion of Individuals Reporting Individual Cognitive Symptoms Occurring at Least Daily.
Among individuals with post–COVID-19 condition, we next used linear regression models to compare individual sociodemographic features with the number of cognitive symptoms reported at least daily. Features associated with a greater number of daily symptoms included younger age and lower income (Figure 2), although age reflected a nonlinear pattern, with greatest symptoms in the 18- to 24-year and 45- to 54-year groups, and least among the 65 years and older group. Characteristics of individuals with or without at least 1 symptom are summarized in Table 2 and the eTable in Supplement 1.
Figure 2. Linear Regression Model of Number of Cognitive Symptoms Associated With Sociodemographic Features.
Individuals who did not select one of the other categories listed for race and ethnicity could instead indicate Other and respond using free text. African American includes African American or Black. OR indicates odds ratio.
Table 2. Individuals With Post–COVID-19 Condition Who Did or Did Not Report Any Cognitive Symptoms Occurring at Least Daily.
| Characteristic | No. (%) | P value | ||
|---|---|---|---|---|
| No cognitive symptoms (n = 728) | Cognitive symptoms (n = 955) | Total (n = 1683) | ||
| Respondent age, mean (SD), y | 49.8 (15.2) | 44.6 (14.2) | 46.9 (14.9) | <.001 |
| Range | 18.0-87.0 | 18.0-86.0 | 18.0-87.0 | |
| Gender | ||||
| Female | 549 (75.4) | 784 (82.1) | 1333 (79.2) | <.001 |
| Male | 179 (24.6) | 171 (17.9) | 350 (20.8) | |
| Race and ethnicity | ||||
| African American or Black | 60 (8.2) | 69 (7.2) | 129 (7.7) | .87 |
| Asian American | 12 (1.6) | 16 (1.7) | 28 (1.7) | |
| Hispanic | 66 (9.1) | 89 (9.3) | 155 (9.2) | |
| Othera | 37 (5.1) | 41 (4.3) | 78 (4.6) | |
| White | 553 (76.0) | 740 (77.5) | 1293 (76.8) | |
| Education | ||||
| Graduate degree | 80 (11.0) | 105 (11.0) | 185 (11.0) | .56 |
| College degree | 256 (35.2) | 301 (31.5) | 557 (33.1) | |
| Some college | 220 (30.2) | 305 (31.9) | 525 (31.2) | |
| High school graduate | 150 (20.6) | 208 (21.8) | 358 (21.3) | |
| Some high school or less | 22 (3.0) | 36 (3.8) | 58 (3.4) | |
| Income, $ | ||||
| Missing | 0 | 1 | 1 | .08 |
| <25 000 | 135 (18.5) | 219 (23.0) | 354 (21.0) | |
| 25 000 to < 50 000 | 205 (28.2) | 280 (29.4) | 485 (28.8) | |
| 50 000 to <100 000 | 262 (36.0) | 310 (32.5) | 572 (34.0) | |
| ≥100 000 | 126 (17.3) | 145 (15.2) | 271 (16.1) | |
| Urbanicity | ||||
| Rural | 164 (22.5) | 233 (24.4) | 397 (23.6) | .61 |
| Suburban | 424 (58.2) | 535 (56.0) | 959 (57.0) | |
| Urban | 140 (19.2) | 187 (19.6) | 327 (19.4) | |
| Impairment | ||||
| Not at all | 133 (18.3) | 62 (6.5) | 195 (11.6) | <.001 |
| A little bit | 407 (55.9) | 413 (43.2) | 820 (48.7) | |
| Moderately | 127 (17.4) | 277 (29.0) | 404 (24.0) | |
| Quite a bit | 44 (6.0) | 143 (15.0) | 187 (11.1) | |
| Extremely | 17 (2.3) | 60 (6.3) | 77 (4.6) | |
| Employment | ||||
| Full-time | 296 (40.7) | 373 (39.1) | 669 (39.8) | <.001 |
| Gig/contract | 1 (0.1) | 9 (0.9) | 10 (0.6) | |
| Homemaker | 48 (6.6) | 79 (8.3) | 127 (7.5) | |
| Parttime | 71 (9.8) | 102 (10.7) | 173 (10.3) | |
| Retired | 183 (25.1) | 136 (14.2) | 319 (19.0) | |
| Self-employed | 45 (6.2) | 83 (8.7) | 128 (7.6) | |
| Student | 15 (2.1) | 31 (3.2) | 46 (2.7) | |
| Unemployed | 69 (9.5) | 142 (14.9) | 211 (12.5) | |
| PHQ-9 total score | ||||
| Not administered | 10 | 19 | 29 | <.001 |
| Mean (SD) | 6.1 (5.4) | 12.2 (6.9) | 9.5 (7.0) | |
Abbreviation: PHQ-9, 9-item Patient Health Questionnaire.
Other includes Native American, Pacific Islander, or individuals who identified “Other” and responded using free text.
We further examined the number of cognitive symptoms reported daily among individuals with post–COVID-19 condition and mood and daily functioning. In regression models, the number of cognitive symptoms reported at least daily was associated with greater severity of depressive symptoms on the PHQ-9 (unadjusted coefficient, 1.40 [95% CI, 1.29-1.51]; adjusted coefficient, 1.27 [95% CI, 1.17-1.38]) (eFigure 3 in Supplement 1). eFigure 4 in Supplement 1 shows a heatmap of correlations between Neuro-QoL item scores and PHQ-9 item scores. More daily cognitive symptoms were associated with a greater likelihood of reporting at least moderate interference with functioning (unadjusted OR, 1.31 [95% CI, 1.26-1.36]; AOR, 1.30 [95% CI, 1.25-1.36]) (Figure 3) as well as lesser likelihood of full-time employment (unadjusted OR, 0.95 [95% CI, 0.91-0.99]; AOR, 0.92 [95% CI, 0.88-0.96]) (eFigure 5 in Supplement 1). After including depressive symptoms in regression models, significant findings noted in crude models between cognitive symptoms and at least moderate interference with functioning were also significant in adjusted models (AOR, 1.27 [95% CI, 1.21-1.33]) and between cognitive symptoms and employment status (AOR, 0.92 [95% CI, 0.88-0.97]) (eFigure 6 and eFigure 7 in Supplement 1).
Figure 3. Logistic Regression Model of Full-Time Employment Examining Number of Cognitive Symptoms Reported at Least Daily and Sociodemographic Features.
Individuals who did not select one of the other categories listed for race and ethnicity could instead indicate Other and respond using free text. African American includes African American or Black. OR indicates odds ratio.
Discussion
In this survey-based cohort of 14 767 individuals with past or current COVID-19 symptoms, 955 of 1683 (56.7%) of those with post–COVID-19 condition described experiencing at least 1 cognitive symptom on a daily basis, substantially more than those without post–COVID-19 condition (27.1%). Prevalence of these symptoms was markedly different between sociodemographic subgroups, with greater cognitive symptoms reported among younger individuals, women, and those with lower levels of income.
Our finding that more than 50% of individuals with post–COVID-19 condition experience at least 1 cognitive symptom on a daily basis is consistent with 46% of individuals with post–COVID-19 condition in a survey of 2359 US adults that asked more generally about cognition.25 Our results extend a growing body of research on the cognitive sequelae of COVID-19, clarifying both the nature of such symptoms and their correlates in a nationally representative cohort reflective of late-pandemic post–COVID-19 condition prevalence.
Our finding of greater daily cognitive symptoms in post–COVID-19 condition in women vs men aligns with prior work that has reported female sex as a risk factor for post–COVID-19 condition.38,39 That younger age is associated with increased daily cognitive symptoms may reflect increased salience of symptoms or change from pre-COVID-19 baseline, in younger individuals relative to older individuals who may already be experiencing age-associated cognitive decline. The apparent nonlinear association herein merits further study, as the age 45- to 54-year group also exhibited substantial rates of such symptoms similar to those of the 18- to 24-year group. The association between cognitive symptoms and lower income suggests that economic stress and its correlates may confer vulnerability to cognitive sequelae in post–COVID-19 condition.
We further found that individuals with a greater number of cognitive symptoms also have a significantly greater burden of depressive symptoms, on average. As both sets of symptoms may reflect brain involvement in COVID-19 sequelae, this association is not unexpected. However, to date, the role of depressive symptoms in post–COVID-19 condition has received relatively little study.40,41 In part, this may represent the complexity of examining causation. Individuals with post–COVID-19 condition, particularly in the pandemic, may have initially been diagnosed with depression or anxiety, before post–COVID-19 condition as a syndrome was recognized. Our observation of the overlap between cognition and mood in post–COVID-19 condition does not in any way suggest any causal relationship, as the association may be bidirectional and/or may reflect a shared underlying mechanism.
Cognitive symptoms were also associated with greater likelihood of describing moderate or greater difficulties of post–COVID-19 condition symptoms in daily life and reduced likelihood of full-time employment. These findings extend the prior report23 and early work conducted in the initial phases of the pandemic that suggested associations between cognitive dysfunction, working capacity, and daily functioning.19,42 Neither association was meaningfully changed by incorporating depressive symptoms in regression models, suggesting that cognitive symptoms are not simply a proxy for or manifestation of depression. This finding is in line with that of Walker et al,21 who reported that cognitive dysfunction, but not depression, was associated with the ability to work after COVID-19. More broadly, our results further underscore the potential economic impact of post–COVID-19 condition.43
Taken together, these results suggest the importance of considering cognitive symptoms in the evaluation and management of post–COVID-19 condition, as they are associated with differences in functioning (as measured herein by self-report of daily impact, as well as employment status) and quality of life (as measured herein by depressive symptoms). They also underscore the need to better understand the biological mechanism underlying these factors to develop effective treatments. Preliminary work indicates, for example, that cognitive dysfunction may be associated with altered gray matter volume, white matter integrity, and functional connectivity in cortical, subcortical, and cerebellar regions.44,45
Limitations
Our study has multiple limitations. Most important, since data collection uses a nonprobability design in which participants opt in, we cannot reliably calculate response rate or estimate nonresponse bias. Prior validation studies from this survey suggest concordance with probability-sampled polls and administrative data.46,47 We also cannot avoid reliance on self-report, including estimates of illness duration. As such, our results complement but do not replace other designs, allowing prospective longitudinal assessment, including objective cognitive testing. The cross-sectional nature of the study also precludes comparison with the prevalence of pre–COVID-19 symptoms. As a broad study not linked to detailed medical history, we cannot examine the association with other comorbidities or treatments that may affect cognition independent of COVID-19 or that may moderate the effects of COVID-19. We also elected not to examine interval from infection or severity of initial infection, previously associated with cognitive symptoms,48 as recall for each of these may be poor. In addition, while we examined associations between cognitive symptoms and depressive symptoms, we note that some items on the PHQ-9 (for example, fatigue and motor slowness) may also capture COVID-19 somatic symptoms rather than features of major depression per se. Prior investigation suggested the validity of the PHQ-9 even in individuals with a range of neurologic disorders.49
Conclusions
The results of this survey study suggest that cognitive symptoms represent common features of post–COVID-19 condition, encompassing impairments often characterized by the widely used lay term brain fog. In light of their marked association with poorer functioning and quality of life, these symptoms represent important targets for assessment and identifying scalable interventions to remediate cognitive dysfunction in post–COVID-19 condition.
eFigure 1. Mean Score by Item, Long COVID Present Versus Absent
eFigure 2. Count of Symptoms Reported Daily Among Those With a Prior History of COVID-19
eTable. Individuals With Long COVID Who Did, or Did Not, Report Any Cognitive Symptoms Occurring at Least Daily – Row Rather Than Column Totals
eFigure 3. Linear Regression Model of PHQ-9
eFigure 4. Correlations Between Individual Cognitive and PHQ-9 Items
eFigure 5. Logistic Regression Model of Full-time Employment, Examining Number of Cognitive Symptoms Endorsed at Least Daily
eFigure 6. Logistic Regression Model of Moderate or Greater Functional Impairment, Examining Number of Cognitive Symptoms Endorsed at Least Daily, Including PHQ9 Total Score
eFigure 7. Logistic Regression Model of Full-time Employment, Examining Number of Cognitive Symptoms Endorsed at Least Daily, Including PHQ9 Total Score
Data Sharing Statement
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
eFigure 1. Mean Score by Item, Long COVID Present Versus Absent
eFigure 2. Count of Symptoms Reported Daily Among Those With a Prior History of COVID-19
eTable. Individuals With Long COVID Who Did, or Did Not, Report Any Cognitive Symptoms Occurring at Least Daily – Row Rather Than Column Totals
eFigure 3. Linear Regression Model of PHQ-9
eFigure 4. Correlations Between Individual Cognitive and PHQ-9 Items
eFigure 5. Logistic Regression Model of Full-time Employment, Examining Number of Cognitive Symptoms Endorsed at Least Daily
eFigure 6. Logistic Regression Model of Moderate or Greater Functional Impairment, Examining Number of Cognitive Symptoms Endorsed at Least Daily, Including PHQ9 Total Score
eFigure 7. Logistic Regression Model of Full-time Employment, Examining Number of Cognitive Symptoms Endorsed at Least Daily, Including PHQ9 Total Score
Data Sharing Statement



