Table 2 Overview of who is included in data collection

Group 1

Canada/CCAHS

Symptoms: experiencing symptoms three or more months after initial COVID-19 symptoms/positive test/thought had COVID-19

Stratified sample representative of adults at the provincial and national level aged 18+ years

Approximately 32 500

• Includes individuals with and without COVID-19 infection

• Includes individuals self-reporting experiencing and not experiencing long COVID symptoms

Switzerland/Zurich Vaccine Cohort

Diagnosis: having received a diagnosis from a clinician;

Self-identify: participants self-identifying as having long COVID and

Symptoms: based on WHO and NICE recommendations, self-reporting still experiencing symptoms more than 3 months after infection

Age stratified random sample of adults 18+ years old attending vaccine centre for their first vaccine in Zurich

575

• Includes individuals with and without COVID-19 infection

• Includes individuals self-reporting experiencing and not experiencing long COVID symptoms

• Individuals with COVID-19 infection from study E7

United Kingdom/ONS CIS

Symptoms: experiencing symptoms more than 4 weeks after they first had COVID-19 (not reliant on positive test result), that are not explained by something else (based on NICE definition)

Individuals aged 2+ years, randomly selected from households in the United Kingdom where a member had previously participated in an ONS or NISRA survey

Approximately 21 000 individuals from 10 000 households

• Includes individuals with and without COVID-19 infection

• Includes individuals self-reporting experiencing and not experiencing long COVID symptoms

Group 2

Belgium/COVIMPACT

Diagnosis: having received a diagnosis from a clinician and

Symptoms: in line with NICE guidelines, long COVID defined as having symptoms related to COVID-19 more than 3 months after the acute infection

Adults aged 18+ years living in Belgium who received a positive PCR test at a national testing centre were sent an invitation to the baseline survey when contacted by the test and trace team

10 708

• Individuals that recovered and did not experience long COVID symptoms

• Matched control from the Belgian Health Interview Survey on the basis of age, sex and level of education

Germany/NAPKON

Symptoms: persistent symptoms after testing positive for COVID

Cross-sectional platform (SUEP): individuals of any age attending inpatient and outpatient settings with confirmed acute SARS-CoV-2 infection. All university and non-university hospitals and primary care practices can become study sites. Some mobile study teams cover long-term care and rehabilitation facilities

High-Resolution Platform (HAP): adults (≥ 18 years) with SARS-CoV-2 hospitalized at one of the 10 participating university hospitals

Population-Based Platform (POP): adults (≥ 18 years) living in one of the three study regions who had a positive test recorded and contacted by local health authority at least 6 months before the start of the study. Individuals with acute re-infection at the time of the interview or scheduled site visit are excluded

Participating study sites consecutively enrol all eligible patients. The recruitment for each cohort is balanced for disease severity. Additional stratification criteria for age, sex, infection date or vaccination status apply depending on the cohort

7093 total:

SUEP: 2749

HAP: 710

POP: 3634

There is no overlap between the cohorts

Comparator respiratory infections

Netherlands/RIVM long COVID

Symptoms: experiencing symptoms for at least 2 months, which are significantly elevated compared with controls

Prospective cohort: individuals (aged 5+ years) who received a positive test for COVID at a national test and trace centre invited to participate when contacted by the municipal health service informing them of their test results. Had to complete the baseline questionnaire within 7 days of the positive test

Retrospective cohort: individuals (aged 5+ years) who tested positive for COVID at a national test centre and DID NOT complete the baseline questionnaire within 7 days. Individuals who self-identify as having long COVID and had COVID at any time since the start of the pandemic (confirmed by test or unconfirmed) could self-enrol

Study includes 50 000 participants total

Prospective cohort: 8000–9000

• Negative COVID test result

• Matched control from the Basic Registration of Persons without a positive test for SARS-CoV-2 infection or known history of probable infections

Switzerland/Zurich coronavirus cohort

Diagnosis: having received a diagnosis from a clinician;

Self-identify: participants self-identifying as having long COVID; and

Symptoms: based on WHO and NICE recommendations, self-reporting still experiencing symptoms more than 3 months after infection

Age-stratified random sample of adults aged 18+ years who had a positive lab test reported to the local public health authorities in the Canton of Zurich

All close contacts were tested and a selection of close contacts that tested negative were tested again at the end of quarantine period. Close contacts that tested positive invited to participate in the study as index cases

1552

Individuals that recovered and did not experience long COVID symptoms

Group 3

Italy/long-CoViD CCM

No formal definition of long COVID; the study is examining the impact of the post COVID phase of the disease by following individuals beyond the acute infection period

Adults aged 40+ years in regional administrative database with a COVID-19 laboratory test results recorded

600 000 individuals (300 000 positive test; 300 000 negative test)

Matched control negative test result

Netherlands/NIVEL-PCD

Symptoms: COVID-19 confirmed by laboratory test in GP data (or during the first wave suspected by algorithm) and experiencing symptoms 3–12 months after infection that were not present or less severe before COVID-19 infection

Strict definition: at least two symptoms recorded in International Classification of Diseases (ICD) codes judged to be related to COVID-19 or post COVID by experts (one of which must be a so-called core symptom – a symptom/complaint identified on the basis of comparison with controls or WHO definition) 3–12 months after infection and visited a GP more than two times for these symptoms

Broader definition: at least two symptoms recorded in ICD codes judged to be related to COVID-19 or post COVID by experts (one of which must be a so-called core symptom – a symptom/complaint identified on the basis of comparison with controls or WHO definition) 3–12 months after infection. Does not include GP visits as anecdotal evidence suggesting that a number of individuals with post COVID are seeking care from other sources and did not want to miss this group

EHR: All patients who seek care at a GP in the NIVEL network

Corona cohort: individuals with a positive COVID infection (either from municipal health service or before community testing set-up, identified on the basis of symptoms in patient record) automatically flagged in GP records

EHR: Approx. 1.7 million individuals from 500 GP practices

Corona cohort: 442 patients with COVID infection from 25 GP practices

• EHR: matched control negative test result

• EHR: before and after COVID pandemic

• Corona cohort: includes individuals self-reporting experiencing and not experiencing long COVID symptoms

Sweden/SCFI-PEARL

Diagnosis/clinical codes: Initially used UO-9, ICD-10 code

Symptoms: symptom profiles recorded in EHR

All individuals with a positive PCR test result identified from SmiNet (the national register of notifiable communicable diseases managed by the Public Health Agency of Sweden)

Whole Swedish population

Random sample of general population from the national register of the Total Population at Statistics Sweden

United Kingdom/CVD-COVID-UK/COVID-IMPACT

Diagnosis/clinical codes: SNOMED-CT codes in primary care data and ICD-10 codes in hospital data

All patients in routine health datasets

England: 57 million

Scotland: 5.5 million

Wales: 3.2 million

Feasible to construct controls within dataset

Group 4

Belgium/Post COVID pathway

Clinical assessment: still suffering from symptoms related to COVID-19 (fatigue, shortness of breath and cognitive dysfunction, among others) having a visible impact on their daily life 12 weeks after first symptoms of COVID-19 infection and/or 12 weeks after a positive COVID-19 test

All patients in GP records who had entered the long COVID Care pathway

Unknown

None

Canada/PC-ICCN

Clinical assessment: based on GP’s assessment. Eligibility based on WHO’s definition of having had confirmed COVID-19 infection either hospitalized or managed as outpatients and experiencing symptoms for 12 weeks or more that could not be explained by an alternative diagnosis

All adults aged 18+ years referred by a primary care provider to one of five post-COVID recovery clinics

October 2022:

7649 clinic visits with 3241 patients

6176 questionnaires completed by 3366 patients

None

Germany/ABC19

Clinical assessment: GPs are provided with a list of symptoms in a public catalogue to guide their clinical decision making, but study has not provided any clear criteria to define a long COVID patient

Any GP offices can sign-up to participate

GPs recruited patients aged 14+ years attending with acute COVID infection. Amended to include any patients who had previously had a confirmed COVID infection and were seeking care for COVID related symptoms

400 patients from 16 GP offices

None

Italy/National surveillance

Not defined. Recruited any individual attending any service for long COVID on the basis of self-definition

Recruited any clinic or centre providing services to people with long COVID. Includes both single specialty sites and multidisciplinary sites, as well as those that were set up specifically to treat long COVID and those that were not. Does not include primary care

Participating facility required to recruit at least 20 patients (12 +) per month. Centres with a higher case volume could choose to select an index week in the month and recruit all patients in that week if they wished

137 centres from 17 Italian regions and two autonomous provinces registered on the online platform. Of these, 124 (90.5%) from 16 regions and two autonomous provinces completed the online questionnaire

None

England/NHSE long COVID registry

Clinical assessment: GP or other clinician can refer patient with ongoing symptoms lasting 4 weeks or more following COVID illness

All patients attending a post COVID service for an initial assessment or triage

99 adult and 10 children services

July 2023; 113 453 individuals referred

None

Group 5

Aotearoa New Zealand/long COVID registry

Self-identify: based on experiencing symptoms for 12 weeks or more after acute infection. People who are unsure whether symptoms are long COVID can completed a quiz at longcovidsupport.co.nz

Adults aged 18+ years living in New Zealand with self-reported long COVID

Aiming to recruit 3000

(1348 as of March 2024)

Possibility to undertake some matching in routine health data