Table 2.

Summaries of included publications.

Study	Design	Population	Age	Time of assessment	Location	Diagnostic Tool	Findings
Mazza et al. (2021)	Uncontrolled observational study	226 patients (67% hospitalized) 66% male	Mean = 58.5 SD = 12.8 Range: 26-87	Mean of 90 days post discharge or ED evaluation (SD = 13.4), previous assessment at one-month follow-up	Milan, Italy	DSM-5, BDI-13, ZSDS	Frequency: •8.9% of patients diagnosed with clinically-significant depression (DSM-5), same result with BDI-13 (≥9). •28% of patients with depressed mood based on ZSDS (≥50).
							Factors: •Female sex (Wilks' λ = 0.92, F = 5.76, p = 0.003), previous psychiatric history (Wilks' λ = 0.93, F = 5.29, p = 0.006), and psychopathology at one-month follow-up (Wilks' λ = 0.82; F = 15.16; p < 0.001) were predictors of depression at three-month follow-up in a multivariate analysis. •No effect of age on self-reported depression scores. •Length of hospital stay is inversely correlated with ZSDS (r = −0.23, p = 0.005, q = 0.01) and BDI-13 scores (r = −0.21, p = 0.010, q = 0.015). •Baseline systemic immune-inflammation index (SII) (ZSDS: χ2 = 42.417, p < 0.0001; BDI-13: χ2 = 56.536, p < 0.0001) and changes of SII (ZSDS: Wald W2 = 6.881, p = 0.0087; BDI-13: Wald W2 = 14.304, p = 0.0002) were predictors of depression and changes of depression at three-month follow-up.
							Other findings: •Persistent depressive symptoms from one-month follow-up to three-month follow-up, in contrast with significant decrease of PTSD symptoms, anxiety and insomnia. •Depression had a significant effect on neurocognitive functioning and ZSDS scores specifically predicted performance in selective attention and processing speed (Wald = 8.37, p = 0.003).
Mattioli et al. (2021)	Prospective cohort study	120 patients with mild-moderate COVID-19 (2% hospitalized), health care workers 30 controls, matched for age, sex and main comorbidities, health care workers 25% male	Mean = 47.9 Range: 26-65	Mean of 126 days from diagnosis (Range: 12–215)	Brescia, Italy	DASS-21	Frequency: •DASS-21 depression scores were significantly higher in COVID-19 subjects than in controls (x̅ = 3 vs. x̅ = 1, p = 0.036).
							Other findings: •DASS-21 depression scores significantly influenced many neuropsychological test scores: MMSE (β = −0.039, p = 0.007) CVLT immediate recall (β = −0.432, p = 0.016), TEA visual RT (β = 6.298, p = 0.007), TOL (β = −0.149, p = 0.008), Rey figure copy and recall (β = −0.096, p = 0.044).
Rass et al. (2021)	Uncontrolled observational study	98 out of 135 patients (23% required ICU care, 53% were admitted to the regular ward, 24% were outpatients) 61% male	Median = 56 IQR: 48-68 Range: 19-87	Median of 102 days from diagnosis (IQR: 91–110)	Tyrol, Austria	HADS-D	Frequency: • 11% of patients with depressive symptoms: o 7% with mild depressive symptoms (HADS-D score >7) o 3% with clinically-significant depression (HADS-D score >10)
							Factors: •Severity of the disease does not significantly influence the frequency of depressive symptoms at 3-month follow-up.
González et al. (2021)	Uncontrolled observational study	59 of 62 patients who required ICU admission for ARDS secondary to COVID-19 74.2% male	Mean = 60 Range: 48-65	3 months after hospital discharge	Lleida, Spain	HADS-D	Frequency: •15.2% of patients with depressive symptoms: o 10.2% with borderline abnormal scores (HADS-D score >7 and ≤ 10) o 5.0% with clinically-significant depression (HADS-D score >10)
Morin et al. (2021)	Uncontrolled observational study	170 out of 177 hospitalized patients (54.8% required ICU care) 62% male	Mean = 56.9 SD = 13.2	Median of 125 days after hospital discharge (IQR: 94–128)	Paris region, France	BDI-13	Frequency: •20.6% of patients with depressive symptoms (BDI-13 > 7), notably 18.1% of ICU patients. •Depressive symptoms observed in 18.0% of intubated patients and in 21.7% of non-intubated patients. •30.8% of patients ≥75 yr with depressive symptoms vs 19.7% of patients <75 yr.
van den Borst et al. (2020)	Uncontrolled observational study	124 patients (16.1% with critical disease, 20.9% with severe disease, 41.1% with moderate disease, 21.7% with mild disease) 60% male	Mean = 59 SD = 14	Mean of 13.0 weeks after onset of symptoms (SD = 2.2) Mean of 9.1 weeks after discharge for hospitalized patients (SD = 1.6)	Nijmegen, Netherlands	HADS-D	Frequency: •12% of patients with clinically-significant depression (HADS-D > 10), notably 22% of patients with mild disease and 10% of patients with critical disease.
							Factors: •Severity of the disease does not significantly influence the frequency of depression at 13-week follow-up.
Frontera et al. (2021)	Prospective cohort study	136 of 196 patients with neurological complications during hospitalization for COVID-19 143 of 186 COVID-19 controls, matched for age, sex, race/ethnicity, and intubation status 65% male	Median = 68 IQR: 55-77	Median of 6.7 months from neurological symptom onset (or COVID-19 symptom in controls) (IQR: 6.5–6.8)	New York, USA	Neuro-QoL	Frequency: •29% of patients with neurological complications scored worse than average on depression section of Neuro-QoL (T score >50) •22% of COVID-19 controls scored worse than average on depression section of Neuro-QoL (T score >50)
							Factors: •No significant difference between both groups.
Daher et al. (2021)	Uncontrolled observational study	18 patients who required ICU admission for ARDS secondary to COVID-19 61% male	Mean = 61 SD = 7	Mean of 197 days after hospital discharge (SD = 15)	Aachen, Germany	PHQ-9	Frequency: • 27% of patients with moderate to severe depressive symptoms (PHQ-9 > 9), all with type L pneumonia (less severe cases than patients with type H pneumonia): o 22% with moderate depressive symptoms (PHQ-9 > 9 and ≤ 14) o 5% with severe depressive symptoms (PHQ-9 > 14)
							Factors: •No significant difference in depression scores of patients with type H or L pneumonia.

DSM-V, Diagnostic and Statistical Manual of Mental Disorders; BDI-13, 13-items Beck's Depression Inventory; ZSDS, Zung Self-rating Depression Scale; DASS-21, Depression, Anxiety and Stress Scale; HADS-D, Hospital Anxiety and Depression Scale - Depression; Neuro-QoL, Quality of Life in Neurological Disorders; PHQ-9, Patient Health Questionnaire; MMSE, Mini–Mental State Examination; CVLT immediate recall, California Verbal Learning Test immediate recall for verbal memory; TEA visual RT, visual reaction times section of the TEA attention test; TOL, Tower of London test for executive abilities.