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The cohort consists of almost 55\u2009000 participants aged 35\u201369 years at the time of recruitment. From 2020 to 2022, ATP conducted a longitudinal substudy, the COVID-19 Antibody Testing (CAT) study, nested in this existing cohort, to understand the spread and impact of the SARS-CoV-2. In this cohort profile, we describe the CAT study design, recruitment and initial findings.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Participants<\/jats:title>\n                    <jats:p>In this prospective cohort substudy, ~4000 participants completed online surveys and provided blood samples at a study centre every 4\u2009months for 1 year, across four cities in Alberta, Canada. The study was launched on a rolling basis beginning in September 2020 and data collection was completed in May 2022. The surveys collected information on health and lifestyle factors, COVID-19 (testing, symptoms, vaccination, public health recommendations) and impacts of the pandemic (including economic, health services, mental health). Blood samples were tested for antinucleocapsid and antispike protein SARS-CoV-2 antibodies.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Findings to date<\/jats:title>\n                    <jats:p>A total of 4102 participants consented and attended a study centre at baseline, and almost 90% of these completed the study. Overall, participants were aged 61\u00b110 years, 60% female, 12% came from rural areas, 45% had at least a bachelor\u2019s degree, 24% reported a household income &lt;$C75 000 and 39% were retired. About 15% of participants tested positive for antibodies induced by a SARS-CoV-2 infection over the course of the study, and about 18% of those who were infected reported long COVID (persistent symptoms for &gt;4 weeks). By the end of the study, 96% of participants had received at least one COVID-19 vaccine dose. Through investigating other outcomes, it was observed that participants under 50 years of age were more likely to be assessed to have mild or moderate-to-severe anxiety and depressive symptoms compared with older participants. In addition, approximately 15% of participants reported a moderate to major impact on their ability to meet financial obligations.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Future plans<\/jats:title>\n                    <jats:p>Serology results, together with health, lifestyle and sociodemographic data, and the continued follow-up of these participants as part of the broader ATP cohort study (planned through 2065), will provide opportunities to investigate the long-term sequelae of COVID-19 infection as well as the broader impacts of the pandemic on physical, mental and emotional health. Data are available to researchers on request through the ATP access process.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1136\/bmjopen-2025-101336","type":"journal-article","created":{"date-parts":[[2025,11,13]],"date-time":"2025-11-13T13:00:22Z","timestamp":1763038822000},"page":"e101336","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":1,"title":["COVID-19 antibody testing study: a nested substudy within Alberta\u2019s Tomorrow Project (ATP) in Alberta, Canada"],"prefix":"10.1136","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-0309-1238","authenticated-orcid":false,"given":"Sara","family":"Nejatinamini","sequence":"first","affiliation":[{"name":"Alberta\u2019s Tomorrow Project, Cancer Research & Analytics, Cancer Care Alberta, Calgary, Alberta, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Carmen","family":"Charlton","sequence":"additional","affiliation":[{"name":"Public 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Department of Medicine, Cumming School of Medicine, Calgary, Alberta, Canada"},{"name":"Department of Pathology & Laboratory Medicine, Cumming School of Medicine, Calgary, Alberta, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"James D","family":"Kellner","sequence":"additional","affiliation":[{"name":"Department of Pediatrics, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada"},{"name":"Alberta Children\u2019s Hospital Research Institute, University of Calgary, Calgary, Alberta, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kristyn","family":"Lines","sequence":"additional","affiliation":[{"name":"Alberta\u2019s Tomorrow Project, Cancer Research & Analytics, Cancer Care Alberta, Calgary, Alberta, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kathleen","family":"Murdoch","sequence":"additional","affiliation":[{"name":"Alberta\u2019s Tomorrow Project, Cancer Research & Analytics, Cancer 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