Table 2. Persistent symptoms, and disease severity reported in the included studies.

Author (year)	Post-acute COVID-19 syndrome*	Length of stay in the hospital (days)	Severity (n) (types of tratament)	Severity rating	Main results
Frontera et al., 52 (2022)	6 and 12 months	-	Intubation Worts SOFA score Lowest oxygen saturation	Severe Light Light	Below-normal MoCA scores were observed in 50% of patients without cognitive impairment, regardless of the presence or absence of a neurological complication during hospitalization. But with improvement at six- and 12-month follow-up.
Miskowiak et al., 49 (2022)	12 months	-	-	-	Cognitive impairments were seen after 1 year in half of patients hospitalized with COVID-19, but the cognitive sequelae were stable over time from three months to one year after hospitalization.
Crivelli et al., 18 (2022)	average of 142 days	-	-	-	The results show that deficits can be identified predominantly in executive functions and attention and have a smaller effect on memory and language in outpatients who have had COVID-19.
Pémille et al., 54 (2022)	3 months	-	Intubation O2 Support	Severe Ligth	At baseline the results showed severe acute cognitive dysfunction with abnormal scores on the global MMSE test, affecting mainly executive functions and episodic memory. All patients improved between baseline and follow-up evaluations.
Cristillo et al., 19 (2022)	12 months	-	-	-	Patients who reported cognitive deficits (n = 25) showed a decline in MoCA after one year of discharge.
Larsson et al., 55 (2022)	4 and 12 months	23	Invasive ventilation therapy	Severe	The results showed no improvements between the first and second follow-up.
Kim et al., 56 (2021)	12 months	-	-	-	Overall, 52.7% responders still experienced COVID-19-related persistent symptoms. The main symptoms were difficulty in concentration, cognitive dysfunction, amnesia, depression, fatigue, and anxiety
Holdsworth et al., 35 (2022)	> 3 months	-	-	-	69% reported ≥ 3 ongoing symptoms. Shortness of breath (61%), fatigue (54%) and cognitive problems (47%) were the most frequent symptoms, 17% met criteria for anxiety and 24% depression.
Braga et al., 36 (2022)	Average 8 months	-	Oxygen support Orotracheal Intubation	Ligth Severe	The results showed that previously hospitalized and non-hospitalized COVID-19 survivors had cognitive deficits, but a relevant difference for disease severity.
Carrillo-Garcia et al., 37 (2022)	6 months	-	-	-	Of the survivors at 6 months, more than half of the sample had some of the following sequelae: dyspnea 20%, functional impairment 41.7%, cognitive impairment 31.3% or depressive symptoms 42.4%.
Cecchetti et al., 38 (2022)	10 months	-	-	-	At follow-up, 36% of patients showed an impairment in at least one cognitive domain. 3%, 6% and 6% of patients showed an executive, memory and visual-spatial impairment, respectively, and 21% of subjects showed a multidomain impairment.
Ferrucci et al., 39 (2022)	5 and 12 months	12	Oxygen support	Ligth	Compared to the assessment at 5 months, verbal memory, attention, and processing speed improved significantly after 1 year, whereas visuospatial memory did not. The most affected domains after 1 year were processing speed, long-term visuospatial and verbal memory.
Hadad et al., 40 (2022)	7 months	-	Oxygen support	Light	On the MoCA test, executive functions, particularly phonemic fluency, and attention, were impaired. In contrast, the total MoCA score, and memory and orientation sub scores did not differ from expected ranges
Jaquet et al., 57 (2022)	3 and 6 months	36	Invasive mechanical ventilation	Severe	MOCA was 26 (23–28.5), and cognitive impairment was reported in 17 patients. The most affected domain was delayed recall with a score of 4 (2–4) in a scale of 0–5.
Liu et al., 58 (2022)	6 and 12 months	-	-	-	The incidence of cognitive impairment in survivors 12 months after discharge was 12.45%. Severe COVID-19 was associated with a higher risk of early-onset cognitive decline, late-onset cognitive decline, and progressive cognitive decline, while no severe COVID-19 was associated with a higher risk of early-onset cognitive decline
Mattioli et al., 59 (2021)	4 months	-	Continuous Positive Airway Pressure Mechanical ventilation O2 support	Light Light Light	MMSE resulted within normal limits in all patients, with a statistically significant lower score in ICU patients and the raw mean scores of all the neuropsychological tests resulted significantly lower in ICU than in non-ICU patients.
Nersesjan et al., 62 (2022)	6 months	-	-	-	The cognitive status improved substantially, from 19.2 (95% CI, 15.2-23.2) at discharge to 26.1 (95% CI, 23.1-29.1) for 15 patients with COVID-19 with MoCA evaluations from hospital discharge.
Ollila et al., 63 (2022)	6 months	20	Invasive mechanical ventilation	Severe	The total cognitive score at six months post-COVID differed between the groups (Home group, Hospitalized non-ICU group (WARD) and ICU group). In pairwise comparisons, both ICU and WARD patients performed worse than home group.
Stavem et al., 41 (2022)	8 to 13 months	-	-	-	The proportion of respondents with z-scores lower than -1.5 was similarly small, though with larger effects in post hoc analyses of executive function among older respondents.
Vannorsdall et al., 42 (2021)	4 months	-	-	-	Cognitive deficits were widespread in those with and without ICU stays and occurred most on measures of oral processing speed and verbal fluency as well as learning and memory. Patients requiring at least 48 hours of ICU care demonstrated poorer global cognition and in the executive functioning and working memory.
Kay et al., 20 (2022)	average 7 months	-	-	-	Cognitive deficits were in processing speed, followed by executive functions and attention/working memory; there was more variability in findings about memory (encoding and delayed memory) and language/semantic access domains across sites.
Priftis et al., 21 (2022)	average 2 months	-	Tracheostomy Artificial ventilation	Severe Severe	None of the patients showed impaired performance on measures assessing overall cognitive status, visuo-spatial short-term/working memory, and language production (semantic fluency).
Hartung et al., 60 (2022)	6 months	-	-	-	26% of patients had mild and 1% had moderate cognitive impairment
Del Brutto et al., 52 (2022)	6 and 18 months	–	Mild symptomatic infections No infection	Light Negative	The post-pandemic cognitive decline seen after 6 months occurred primarily in individuals who had COVID-19. After 18 months, the difference in the total MoCA score was not significant between the groups.
Delgado-Alonso et al., 22 (2022)	> 9 months	average of 19	Ventilatory assistance	Light	COVID-19 patients showed decreased performance on tests of attention and executive function, processing speed, working memory, and inhibition; episodic memory; and visuospatial processing.
Zhao et al., 23 (2022)	> 4 months	–	–	–	COVID-19 survivors performed well on most of the cognitive skills tested, including working memory, executive function, planning and mental rotation. They showed changes in episodic memory tests (up to 6 months after infection) and surveillance (up to 9 months).
Latronico et al., 61 (2022)	3, 6 and 12 months	-	Mechanical Ventilation Tracheostomy	Severe Severe	During the evaluations, the prevalence of cognitive deficit in the MoCA exam decreased. At three months there were 23 patients and at 12 months there were seven.
Bonizzato et al., 44 (2022)	3 months	-	-	-	No significant differences were found over time (T0, T1 and T2) to the screening test, but between T0 and T1, the mean scores at MoCA showed a slight difference.
Pilotto et al., 45 (2021)	6 months	average of 11.6	Oxygen support Non-invasive ventilation Intubation	Ligth Moderate Severe	At neurological examination, 40% of patients exhibited neurological abnormalities, such as hyposmia (18.0%), cognitive deficits (17.5%), postural tremor (13.8%) and subtle motor/sensory deficits
Albu et al., 24 (2021)	> 3 months	average of 26	O2 Support Non-invasive ventilation Invasive ventilation	Light Moderate Severe	In patients who received respiratory assistance, persistent cognitive deficits (difficulties in concentration, short-term memory impairment) occurred after recovery. However, there was no difference between the group that did not receive assistance.
Alemanno et al., 46 (2021)	1 month	80	Orotracheal intubation and ventilation Non-invasive ventilation Oxygen therapy with masks Did not need oxygen	Severe Moderate Moderate Light	The orotracheal intubation and ventilation group scored higher than the oxygen therapy group on tests of executive functions, naming, short- and long-term memory, abstraction, and orientation.
Becker et al., 25 (2021)	> 7 months	–	–	–	Hospitalized patients were more likely to have deficits in attention, executive functioning, categorical verbal fluency, and episodic memory than those in the outpatient group. Patients treated in the emergency department were more likely to have impaired categorical verbal fluency and memory than those treated in the outpatient clinic.
Carrillo-Garcia et al., 47 (2021)	3 months	15	–	–	The results showed that among the survivors, two out of three patients continued to have physical disability, cognitive impairment or affective complaints or anorexia.
Dressing et al., 48 (2022)	> 3 months	–	–	–	Patients who had COVID-19 performed above normal in all cognitive domains (verbal memory, visual memory, processing speed, attention, executive function) and on the total MoCA score.
Hosp et al., 26 (2021)	1 month	–	Only observation Non-invasive ventilation Endotracheal ventilation	Light Moderate Severe	MoCA performance was altered in 18/26 patients (mean score 21.8/30) with greater impairment in frontoparietal cognitive functions
Lamontagne et al., 27 (2021)	> 4 months	–	Asymptomatic Mild symptomatic infections	Asymptomatic Light	Individuals with mild symptomatic infections (post-COVID-19) had impairment in executive functioning but not in attentional orientation or alertness, highlighting the specificity of post-infection cognitive dysfunction.
Liu et al., 28 (2021)	6 months	–	Mechanical ventilation High Flow Oxygen Therapy	Moderate Severe	COVID-19 patients had worse cognitive performance 6 months after recovery. In addition, high-flow oxygen therapy during the acute phase of COVID-19, which can alleviate oxygen deficiency, may protect against post-infection cognitive decline.
Miskowiak et al., 34 (2021)	3-4 months	–	–	–	The percentage of patients with clinically significant cognitive impairment ranged from 59% to 65%, depending on the cutoff used, with verbal learning and executive functions being the most affected.
Pistarin et al., 29 (2021)	3 months	–	–	–	The post-covid-19 group, and COVID-19 patients showed deficits in executive function, short- and long-term memory, visuospatial skills, abstraction, and orientation. However, post-COVID-19 patients, one month after infection, performed better in the language subdomain, compared to COVID-19 patients.
Weidman et al., 50 (2022)	1 month	51	Intubation Mechanical ventilation	Moderate Severe	In total, 25% of post-ICU patients had cognitive impairment. However, there were no associations between length of ICU stay, delirium, exposure to benzodiazepines, steroids, or systemic paralytics with positive screening for physical, psychological, or cognitive impairment.
Blazhenets et al., 51 (2021)	> 3 months	–	–	–	A significant improvement in MoCA was observed, relative to the control group, but the average performance was within the mild cognitive impairment range established with the normative data.
Evans et al., 30 (2021)	2-7 months	Class 3- 4: 2 Class 5: 6 Class 6: 10 Class 7-9: 33	class 3–4: no need for continuous supplemental oxygen class 5: continuous supplemental oxygen only class 6: ventilation with continuous positive airway pressure, bilevel positive airway pressure, or high flow nasal oxygen class 7–9: invasive mechanical ventilation or extracorporeal membrane oxygenation	Light Light Moderate Severe	Four clusters were identified with different severity of mental and physical health impairment (n = 767): very severe (131 patients, 17%), severe (159, 21%), moderate together with cognitive impairment (127, 17%) and mild (350, 46%).
Graham et al., 7 (2021)	> 1 month (mean 5.27)	–	–	–	Study data showed that SARS-CoV-2 patients performed worse on cognitive attention and working memory tasks compared to a demographically matched US population.
Hampshire et al., 31 (2020)	> 3 months	–	No disease Asymptomatic No home assistance Home assistance Hospitalized without ventilation Hospitalized with ventilation	No disease Asymptomatic Light Light Moderate Moderate	Data showed that cognitive deficits were of large and moderate effect size for people who were hospitalized (N = 192), but also for non-hospitalized cases who had biological confirmation of COVID-19 infection (N = 326).
Del Brutto et al., 43 (2021)	6 months	–	Mild symptomatic infections No infection	Light Negative	Individuals with a history of mild symptomatic SARS-CoV-2 infections are more than 18 times more likely to develop cognitive decline than those without clinical and serological evidence of infection. .
Almeria et al., 32 (2020)	1 month	average of 25	Oxygen Asymptomatic	Light Asymptomatic	Overall, 34.3% of patients had cognitive complaints after COVID-19 infection, and those who required oxygen therapy had lower scores on the memory, attention, and executive function subtests compared to asymptomatic patients.
Woo et al., 33 (2020)	20–105 days (median, 85 days)	–	Oxygen	Light	78% of patients reported mild cognitive deficits and performed worse on tests of short-term memory, attention, and concentration compared to 10 healthy age-matched controls. However, cognitive outcomes did not correlate with hospitalization, treatment, viremia, or acute inflammation.

Note: * According to Nalbadian et al. ⁵ it is further divided into two categories: (1) subacute or ongoing symptomatic covid-19, which includes symptoms and abnormalities present 4–12weeks after acute covid-19; and (2) chronic or post-covid-19 syndrome, which includes symptoms and abnormalities persisting or present beyond 12 weeks of the onset of acute covid-19.