TABLE 1.

Characteristics of the included studies: methodological summary and main results

First author, Year	Country	Population settings	Age	Sex (F %)	COVID‐19 cases (n Severity)	Healthy controls (n Definition)	Time of assessment	Cognitive test	Results	Adjustment or corrected values
CASE CONTROL
Amalakanti 2021	India	General Hospital	36.2 ± 11.7	52.3	93 Mild	102 PCR	Acute phase of COVID‐19	MoCA	Fluency Cases: 0.9 ± 0.6 vs HC: 1.6 ± 0.7; P <.001 Visuo‐perception Cases: 2.4 ± 0.7 vs HC: 2.8 ± 0.7; P = .032 Naming Cases: 3.6 ± 0.5 vs HC: 3.9 ± 0.2; P = .016 No significant difference between cases and controls in MoCA, executive function, orientation, calculation, abstraction, delayed recall, and attention	Age and sex
Manera 2021	Italy	Hospital	67 ± 13.2	33.5	152 Mild, moderate, and severe	No	3 months after acute infection	MMSE	Impaired MMSE performance was notably more frequently for mild to moderate (26.3%)	Age and education
Ortelli 2021	Italy	Neurorehabilitation Hospital	67 ± 9.6	16.7	12 Moderate	12 HC	3 months after infection	MoCA, FAB, C‐FSS, BDI, AES, and computerized: VT, SIT, and NT task	Montreal Cognitive Assessment (MoCA) Cases; 17.8 ± 5.3 vs HC: 26.8 ± 3.1; P <.001 Frontal Assessment Battery ± FAB Cases: 12.3 ± 2.3 vs HC: 16.7 ± 1.2; P < .001 RT in Vigilance Task ± VT Cases: 341.3 ± 86.3 vs HC: 308.8 ± 44.2; P = .541 Percentage of errors in VT Cases: 4.6 ± 0.8 vs HC: 1.2 ± 0.3; P< .001 RT in Stroop Interference Task ± SIT Cases: 969.4 ± 152.1 vs HC: 802.1 ± 122.0; P = .015 Percentage of errors in SIT Cases: 4.6 ± 0.8 vs HC: 1.2 ±0.3; P = .001 RT in Navon Task ± NT Cases: 1327.1 ± 525.3 vs HC: 850.3; P = .046 Percentage of errors in NT Cases: 3.8 ±1.2 vs HC: 1.2 ± 0.3; P < .001	Age and sex
Raman 2021	UK	General Hospital	55 ± 13	41.4	58 Moderate to severe	38 Health Subjects	2‐3 months after infection	MoCA, FSS, GAD‐7, and PHQ‐9	Executive/visuospatial score < 4 Cases: 40% vs HC: 16%; P = .010 No significant difference between cases and controls in MoCA	Age, sex, BMI, BP, smoking, head size
Triana 2020	Cuba	Neuro Hospital	54.5 ± 12.5	52.3	42 Hospitalized	100 Health Subjects	45 days from covid‐positive	MoCA	MoCA Cases: 23.43 ± 3.054 vs HC: 25.12 ± 3.367); PP= .007 Digit Series Cases: 1.41 ± 0.631 vs HC: 1.74 ± 0.543; P = .005 Attention Cases: 4.51 ± 1.381 vs HC: 5.07 ± 1.166; P = .026 Abstraction Cases: 1.41 ± 0.706 vs HC: 1.71 ± 0.574; P = .021 Delayed recall Cases: 1.78 ± 1.388 vs HC: 2.78 ± 1.567; P = .001 No significant difference between cases and controls in executive/visuospatial, orientation, language, word search, repeating phrases, subtraction, sustained attention, and fluency	Age, sex, and education
Woo 2020	Germany	General Hospital	42.2 ± 14.3	57.9	18 Mild‐ moderate	10 Randomly selected	Median 3 months after recovery	TICS‐M, FSS, PHQ‐9	TICS‐M Total Score Cases: 38.83 (31‐46) vs HC: 45.8 (43‐50); P = .000 TICS‐M Subscores Attention; P = .029 Language and Concentration; P = .009 Memory; P = .004 No significant difference between cases and controls in orientation	Age‐matched healthy controls
Zhou 2020	China	General Hospital	47 ± 10.5	37.9	29 Moderate	29 PCR	2‐3 weeks after infection	iPad‐based online‐ TMT, SCT, CPT, and DST	Missing Number Cases: 41.55 ± 2.90 vs HC: 39.59 ± 2.31; P = .006 CPT part 3 Correct Number Cases: 6.34 ± 2.50 vs HC: 8.21 ± 1.90; P = .002 Missing Number Cases: 40.38± 3.10 vs HC: 38.45 ± 2.13; P = .008 No significant difference between cases and controls in the Trail Making Test and Sign Coding Test.	Age, gender, and education
COHORT
Alemanno 2021	Italy	Hospital	67.2 ± 12.8	29.0	87 Moderate to severe Four severity groups	No	Acute phase of COVID‐19 and 1 month after infection	MoCA, MMSE, HRSD, and DTS	Patients were divided in four groups according to the respiratory support they received in the acute phase of the disease Group 1 had higher scores than Group 3 for visuospatial/executive functions (P = .016), naming (P = .024), short‐ and long‐term memory (P = .010; P = .005), abstraction (P = .024), and orientation (P = .034).	Severity of the respiratory compromise
Becker 2021	USA	Health System Institutional	49.0 ±14.2	63	740 Mild to severe	No	7 months after diagnosis	Digit Span Forwards and Backward, TMT, phonological and category fluency, and HVLT‐R.	Hospitalized patients were more likely to have impairments in attention (odds ratio [OR]: 2.8; 95% CI: 1.3‐5.9), executive functioning (OR: 1.8; 95% CI: 1.0‐3.4), category fluency (OR: 3.0; 95% CI: 1.7‐5.2), memory encoding (OR: 2.3; 95% CI: 1.3‐4.1), and memory recall (OR: 2.2; 95% CI: 1.3‐3.8) than those in the outpatient group. Patients treated in the ED were more likely to have impaired category fluency (OR: 1.8; 95% CI: 1.1‐3.1) and memory encoding (OR: 1.7; 95% CI: 1.0‐3.0) than those treated in the outpatient setting.	Age, no history of dementia and spoke English or Spanish
Crivelli 2021	Argentina	Neurological Clinic	50 ± 43.63	49	45 Mild to severe	45 Health subjects	5 months after illness	MoCA, TMT, Digit Span Forwards and Digit‐Symbol Coding, Craft Story, RAVLT, Benson Figure, WISC, Stroop, MINT, phonological fluency, and HADS	***Significant differences between groups were found in cognitive composites of memory (p = 0.016, Cohen's d = 0.73), attention (P < 0.001, Cohen's d = 1.2), executive functions (p < 0.001, Cohen's d = 1.4), and language (p = 0.002, Cohen d = 0.87).	Age, sex, and education
Dressing 2021	Germany	General Hospital	53.6 ± 12.0	64.5	31 Mild	No	3 months after acute infection	MoCA, HVLT, DST, BVMT‐R, TMT, FWIT, SDMT, fluency	The most frequently impaired domain was visual memory (7/31 [23%] patients; other domains ≤ 2/31 [≤ 7%]). Impaired individual tests on single‐subjects level were most frequently observed for verbal and visual memory tests.	None
Vannorsdall 2021	USA	Clinic	54.5 ± 14.6	59.5	82 (48 severe, 34 moderate)	No	4 months after acute infection	RAVLT, TMT, DST, fluency	67% of patients showed ≥1 abnormal cognitive score. Patients requiring intensive care unit (ICU) stays displayed more severe and heterogenous impairment than those requiring less intensive treatment. Mild/moderate impairment was particularly common on Oral Trail Making Test part A, category‐cued verbal fluency, RAVLT acquisition, and RAVLT delayed recall.	Age
Hellgren 2021	USA	Hospital	59 ± 6.4	25	35 Mild, moderate, and severe	No	5 months after acute infection	RBANS	Sixteen of 35 patients (46%) showed cognitive impairments; 6 of these (17%) showed mildly/moderately impaired cognition, and 10 patients (29%) had severely impaired cognition.	Age
Del Brutto 2021	Ecuador	Atahualpa Residents	62.6 ± 11	63.0	52 Mild	41 PCR	6 months after infection	MoCA, PSQI and HADS	Post‐pandemic MoCA was worse in seropositive mild symptomatic individuals. Cognitive decline was defined as worsening in the post‐pandemic MoCA ≥4 points compared to the reduction experienced between pre‐pandemic baseline and follow‐up MoCA scores. Cognitive decline in 21% seropositive vs 2% seronegative cases. In multivariate analyses, the odds for developing cognitive decline were 18.1 times higher.	Cardiovascular risk factors, sleep quality, depression and education
Ermis 2021	Germany	Hospital	63	39.6	53 Moderate to severe	No	Acute phase of COVID‐19	MoCA	Cognitive impairment with deficits primarily in executive function, attention, language. and delayed recall.	None
Mattioli 2021	Italy	University Hospital	53.4 ± 9.2	62.7	163 Mild and moderate, 52 severe	No	4 months after acute infection	COWA‐S, ROCFT, CVLT, RAVLT, TOL	Mild and moderate COVID patients show impairment in TOL (in 24 cases, 15%), Rey figure recall (in 13 cases, 8%), and Rey figure copy (in 8 cases, 5%). In severe COVID patients, the impairment also included the verbal memory test (delayed RAVLT in 4 cases (7.7%); immediate RAVLT in 3 patients (5.7%).	Age and education
Méndez 2021	Spain	General Hospital	57 IQR [49,67]	41.3	179 Moderate to severe	No	2 months after discharge	Telephone: SCIP, ANT, COWAT, WAIS IV, Digit span forward and backward, GAD‐7, PHQ‐2, and 17 DTS	Neurocognitive domain impairment was predefined as moderate/severe impairment of any of the four neuropsychological tests. 105 patients (58.7%) met criteria for moderate neurocognitive impairment and 33 (18.4%) for severe neurocognitive impairment Immediate verbal memory impairment 38% moderate, 11.2% severe Delayed memory: 11.8% moderate impairment and 2.8% severe impairment. Semantic verbal fluency 34.6% moderate deficits and 8.4% severe deficit Working memory: 6.1% and severely impaired in 1.1%	Age and education
Miskowiak 2021	Denmark	Hospital	56.2 ± 10.6	59.0	29 Moderate to severe	100	3‐4 months after discharge	SCID‐D, TMT B, WMT, VLT, VFT, PMT, and CFQ	SCIP total score Cases: 67.4 ± 13.9 vs HC: 75.0 ± 9.1; P = .010 VLT‐L Cases: 19.9 ± 4.2 vs HC: 22.1 ± 3.0; P = .003 WMT Cases: 18.2 ± 4.2 vs HC: 1.9 ± 2.5; P = .040 VFT Cases: 14.3 ± 4.7 vs HC: 16.0 ± 4.5; P = .170 VLT‐D Cases: 6.3 ± 2.8 vs HC: 7.0 ± 1.9; P = .080 PMT Cases: 9.0 ± 3.2 vs HC: 10.1 ± 2.3; P = .090 TMT‐B Cases: 116.2 ± 65.0 vs Normative Score: 80.6 ±18.7: p = .002 No associations between the severity of COVID‐19 and cognitive functioning in terms of cognitive impairments, length of hospitalization, total oxygen requirements and acute illness severity markers. More global cognitive impairment and executive dysfunction both correlated with severity of respiratory symptoms according to the ACQ. (Spearman's rho: SCIP total score deviation: r = −.56; P = .009; TMT‐B deviation: r = 0.44; P = .020) and CAT (Spearman's rho: SCIP total deviation r = −.39; P = .050; TMT B: r = .64; P < .001) More global cognitive impairment also correlated with poorer pulmonary function, as reflected by lower forced expiratory volume in one second (FEV1; Spearman's rho, r = 0.37; P = .049)	Age, sex and education
Hosp 2021	UK	Hospital	65.2 ± 14.40	38.0	29 Moderate	29 PCR	1 month after symptom	MoCA, HVLT, TMT, Stoop, Digit span forward and backward, Symbol digit modalities test, and Fluency (animals, s‐words)	MoCA global score 26 (max 30). MoCA global score 69% MoCA global score 54% MoCA global score 15% MoCA global score 31% HVLT‐R total 50% Stroop test: Word reading 28.6% Stroop test: Color naming 14.3% Stroop test: Interference 14.3% Digit span forward 20% Digit span reverse 40% Symbol digit modalities test 14.3% Categorical (animals) 46.1% Phonemic (s‐words) 23.1%	Age and presentation of at least one newly acquired neurological symptom
CASE REPORT
Tolentino 2021	Brazil	General Hospital	47	0.0	1 Moderate	No	Acute phase of COVID‐19	MMSE, Go/No‐Go task, CVAT, GAD‐7, and PHQ‐9	On day 1 of illness, the patient reported a subjective attention impairment. On day 3, the patient performed worse than the 75th percentile in two subdomains (variability of reactions time [VRT] and recreation time {RT]), indicating a moderate attention impairment. On day 6, the patient performed worse than the 75th percentile in all variables of the CVAT except commission errors (CE), indicating a severe impairment. VRT is the most affected variable, followed by omission errors (OE). Thus, the sustained‐focused subdomain is the most affected subdomain. On day 10, there was a mild deficit on only one variable (OE). On day 16, his performance was within the normal range.	Sex and age
Yesilkaya 2021	Turkey	General Hospital	29	0.00	1 Mild	No	3 months after the initial diagnosis	FAB, GDS, TMT, and CVLT	A number of errors were detected in both the A and B parts of TMT and the scores were 2 and 4, respectively. The patient repeated 7 words in his first trial of CVLT. Overall, the results suggested impairment in varying spheres of cognition including memory, executive functioning, motor programming, attention, and concentration. After 3 months: The FAB score was 16. No error was detected in part A while the patient made 2 errors in part B of TMT. He repeated 11 words in CVLT. No neurological or cognitive deficits were detected at the patient's follow‐ups.	None
CASE SERIES
Beaud 2020	Switzerland	General Hospital	64.8 ± 7.6	23.0	13 Severe	No	Mean 5.5 (SD 2.4) days from ICU discharge	MoCA and FAB	MoCA Cases: 19.7 ± 7.5 FAB scores Cases: 10.9 ± 5.5	None
Groiss 2020	Germany	General Hospital	59.5 ±17.6	0.0	4 Severe	No	3 weeks after dismissal	MoCA, MMSE, SDMT, and 4AT	MoCA total score Patient 1 Impaired (21) Patient 2 impaired (16) MMSE total score Patient 1 Impaired (−18.81) Patient 2 Impaired (−4.29) Patient 3 Impaired (14)	None
Hellmuth 2021	USA	Memory Clinical and Telemedicine	44.5 ± 11.5	100.0	2 Mild	No	149 days after infection	MoCA, CVLT, MMSE, WAIS IV Digit span forward and backwards, D‐KEFS fluency, TMT, ROCFT, Color word interference, and NAB	Rey Osterrieth Complex Copy Cases: 33/36 low average Figure 2 min delay Cases: 16/36 below average Backward Span Cases. 4 low average Inhibition/switching Cases: 77 low average	None
Negrini 2021	Italy	Rehabilitation Hospital	48.5	33.3	9 Moderate	No	1 month after hospitalization	MMSE, FAB, BDI, and STAI	General cognitive decline was observed in three patients (33.3%), who had pathological MMSE scores. All these patients had low scores in the domain of attention and calculation, short‐term memory, and written language. Only one patient (11.1%) showed decay of executive frontal functioning, as measured by the pathological scores at the FAB test, with deficits in conceptualization, lexical fluency, and motor programming.	Age, sex and education
Whiteside 2021	USA	Rehabilitation Hospital	70 ± 7.0	33.3	3 Severe	No	2 months after acute infection	Telephone: WAIS‐IV (Vocabulary Subtest), RDS, HVLT‐R, RBANS, BDAE, O‐TMT, TSAT, ILS, BAI, and GDS	Neurocognitive deficits after severe COVID‐19 infection, particularly in encoding and verbal fluency.	Age and education

References Instruments: MoCA (Montreal Cognitive Assessment); FAB (Frontal Assessment Battery); FSS (Fatigue Severity Scale); BDI (Beck Depression Inventory); AES (Apathy Evaluation Scale); GAD‐7 (General Anxiety Disorder Scale); PHQ (Patient Health Questionnaire) ; TICS‐M (The modified telephone interview for cognitive status); TMT (Trail Making Test); SCT (Sign Coding Test); CPT (Continuous Performance Test); DST (Digit Span Test); CVAT (Continuous Visual Attention Test); MMSE (Mini‐Mental State Examination); SDMT (Symbol Digit Modalities Test); CVLT (California Verbal Learning Test); NAB (Neuropsychological Assessment Battery); STAI (The State Trait Anxiety Inventory); HVLT‐R (Hopkins Verbal Learning Test Revised); RBANS (Repeatable Battery for the Assessment of Neuropsychological Status); O‐TMT (Oral Trail Making Test); BDAE (Boston Diagnostic Aphasia Examination); HRSD (Hamilton Depression Rating Scale); BNT (Boston Naming Test); ROCFT (Rey Osterrieth Complex Figure Test); HADS (Hospital Anxiety and Depression Scale); PSQI (Pittsburgh Sleep Quality Index); SCIP (Screen for Cognitive Impairment in Psychiatry); ANT (Animal Naming Test); COWAT (Controlled Oral Word Association Test); DTS (Davidson Trauma Scale); VT (Vigilance Task); SIT (Stoop Interference Task); NT (Navan Task); 4AT (Rapid clinical test for delirium); SCID‐D (Cognitive impairment in psychiatry Danish version); CFQ (Cognitive Failures Questionnaire); VLT (Verbal learning Test); WMT (Working Memory Test); VFT (Verbal Fluency Test); PMT (Psychomotor Speed Test); BMT (Babcock Memory Test); PCL (Post‐traumatic stress disorder checklist); BMET (Brief Memory and Executive Test); HVLT (Hopkins Verbal Learning Test); BVMT‐R (Brief Visuospatial Memory Test‐Revised); FWIT (Color‐Word Interference Test); COWA‐S (Controlled Oral Word Association Test); TOL (Tower of London Test); GDS (Geriatric Depression Scale); MINT (Multilingual Naming Test); WISC (Wisconsin Card Sorting Test); WAIS IV (Weschler Adult Intelligence Scale); RAVLT (Rey Auditory Verbal Learning Test); TSAT (Test of Sustained Attention and Tracking); ILS (Independent Living Scale); BAI (Beck Anxiety Inventory).

^*All COVID‐19 cases were defined with RT‐PCR except Beaud et al. 2020, who used the definition of PCR and ARD