← All cohorts · SARS-CoV-2 cohorts
Patient-Led Long COVID international cohort (Davis 2021)
source record (JSON) · schema v2.0.0 · CC BY 4.0
Design notes & limitations. Deliberately included as a methodologically weak but historically pivotal cohort: a large (n=3762, 56 countries) self-selected online convenience sample recruited through patient support communities, with no control group, no laboratory confirmation for most respondents, and self-reported outcomes. Its breadth of symptom characterisation (203 symptoms across 10 organ systems) is unmatched, but the design cannot estimate population prevalence. Useful in the gap matrix to contrast against denominator-defined cohorts.
Identity & trigger
- Cohort id
davis-2021-longcovid- Aliases
- Patient-Led Research Collaborative Long COVID survey
- Outbreak / event
- COVID-19 pandemic (onset before June 2020)
- Pathogen
- SARS-CoV-2 (Virus)
- Exposure ascertainment
- Mixed
Design
- Design
- Survey
- Denominator defined
- No
- Denominator method
- n/r
- Recruitment
- patient organisation
- Time zero
- Self-reported onset of suspected or confirmed COVID-19 (illness lasting >28 days, onset prior to June 2020) (week)
- Control group
- None
Size & attrition
- Enrolled
- 3762
- Analysed / enrolled
- 3762/3762 (100%)
- Max follow-up (months)
- 7
Biospecimens
- Specimens
- No
- Types
- none
- Acute-phase specimens
- No
- Biobank
- N/A
- External access
- Unknown
Observations (7)
Symptoms
80% (78.5–81.6) Proportion
- Measure
- Fatigue sym:fatigue
- As worded
- “fatigue reported among respondents symptomatic after month 6”
- Population
- whole cohort · denominator Unclear · N=measured, not reported
- Timing
- 6 mo (3-6 mo) · ref Not reported
- Method
- Unclear · Structured symptom questionnaire (author-defined)
- Comparator
- no comparator
- Comparability signature
- ac23b7c108 — measure sym:fatigue · Unclear · ref Not reported · denom Unclear · 3-6 mo · Proportion
- Provenance
- Results (most likely symptoms after month 6) · Manual · verified OSMF research-tracker (web-verified against source) on 2026-07-20
73.3% (71.5–75.1) Proportion
- Measure
- Post-exertional malaise sym:post-exertional-malaise
- As worded
- “post-exertional malaise reported among respondents symptomatic after month 6”
- Population
- whole cohort · denominator Unclear · N=measured, not reported
- Timing
- 6 mo (3-6 mo) · ref Not reported
- Method
- Unclear · Structured symptom questionnaire (author-defined)
- Comparator
- no comparator
- Comparability signature
- cf0c586af0 — measure sym:post-exertional-malaise · Unclear · ref Not reported · denom Unclear · 3-6 mo · Proportion
- Provenance
- Results (most likely symptoms after month 6) · Manual · verified OSMF research-tracker (web-verified against source) on 2026-07-20
58.4% (56.5–60.2) Proportion
- Measure
- Cognitive dysfunction sym:cognitive-dysfunction
- As worded
- “cognitive dysfunction reported among respondents symptomatic after month 6”
- Population
- whole cohort · denominator Unclear · N=measured, not reported
- Timing
- 6 mo (3-6 mo) · ref Not reported
- Method
- Unclear · Structured symptom questionnaire (author-defined)
- Comparator
- no comparator
- Comparability signature
- f62e0e5b9f — measure sym:cognitive-dysfunction · Unclear · ref Not reported · denom Unclear · 3-6 mo · Proportion
- Provenance
- Results (most likely symptoms after month 6) · Manual · verified OSMF research-tracker (web-verified against source) on 2026-07-20
80% (78.5–81.6) Proportion
- Measure
- Fatigue sym:fatigue
- As worded
- “fatigue”
- Population
- subgroup · denominator Symptomatic subset · N=n=3762
- Timing
- 6 mo (3-6 mo) · ref Current
- Method
- Structured checklist · Structured symptom questionnaire (author-defined)
- Comparator
- no comparator
- Comparability signature
- 0d684c8005 — measure sym:fatigue · Structured checklist · ref Current · denom Symptomatic subset · 3-6 mo · Proportion
- Provenance
- Results, symptoms after month 6 (fatigue 80.0%, 95% CI 78.5-81.6) · Manual · verified OSMF research-tracker (web-verified against source) on 2026-07-20
73.3% (71.5–75.1) Proportion
- Measure
- Post-exertional malaise sym:post-exertional-malaise
- As worded
- “post-exertional malaise”
- Population
- subgroup · denominator Symptomatic subset · N=n=3762
- Timing
- 6 mo (3-6 mo) · ref Current
- Method
- Structured checklist · Structured symptom questionnaire (author-defined)
- Comparator
- no comparator
- Comparability signature
- a3e8d4514b — measure sym:post-exertional-malaise · Structured checklist · ref Current · denom Symptomatic subset · 3-6 mo · Proportion
- Provenance
- Results, symptoms after month 6 (post-exertional malaise 73.3%, 95% CI 71.5-75.1) · Manual · verified OSMF research-tracker (web-verified against source) on 2026-07-20
58.4% (56.5–60.2) Proportion
- Measure
- Cognitive dysfunction sym:cognitive-dysfunction
- As worded
- “cognitive dysfunction”
- Population
- subgroup · denominator Symptomatic subset · N=n=3762
- Timing
- 6 mo (3-6 mo) · ref Current
- Method
- Structured checklist · Structured symptom questionnaire (author-defined)
- Comparator
- no comparator
- Comparability signature
- 6e6cca3ee5 — measure sym:cognitive-dysfunction · Structured checklist · ref Current · denom Symptomatic subset · 3-6 mo · Proportion
- Provenance
- Results, symptoms after month 6 (cognitive dysfunction 58.4%, 95% CI 56.5-60.2) · Manual · verified OSMF research-tracker (web-verified against source) on 2026-07-20
Functional outcomes
22.3% Proportion
- Measure
- Not working due to illness func:unable-to-work
- As worded
- “not working at time of survey due to illness (a further 45.2% required a reduced work schedule)”
- Population
- whole cohort · denominator Unclear · N=measured, not reported
- Timing
- 7 mo (6-12 mo) · ref Not reported
- Method
- Unclear · Structured symptom questionnaire (author-defined)
- Comparator
- no comparator
- Comparability signature
- f9f068b853 — measure func:unable-to-work · Unclear · ref Not reported · denom Unclear · 6-12 mo · Proportion
- Provenance
- Results (employment impact) · Manual · verified OSMF research-tracker (web-verified against source) on 2026-07-20
Publications
- Davis HE, Assaf GS, McCorkell L, et al. (2021). Characterizing long COVID in an international cohort: 7 months of symptoms and their impact. EClinicalMedicine. PMID 34308300 · DOI 10.1016/j.eclinm.2021.101019 primary
Provenance & verification
- Registration
- n/r
- Funders
- Patient-Led Research Collaborative (self-funded)
- Related cohorts
- none
- Symptom-inventory scope
- Comprehensive inventory
- Last verified
- 2026-07-20 — OSMF research-tracker (web-verified against source)