Action to beat Coronavirus Study [Ab-C, study data contributed to the CITF Databank]

<b>Background:</b> In the early months of the COVID-19, the spread of disease was poorly understood. Looking at serological evidence of past SARS-CoV-2 infection can help determine the spread of the disease in the general population and quantify levels of population immunity. Through a partnership with the Angus Reid Institute, a polling firm, the Ab-C study rapidly recruited Canadians in the first year of the pandemic and tailored follow-up surveys to the ever-changing COVID-19 pandemic. <br>

<b>Aims of the CITF co-funded study:</b> Ab-C aimed to understand the prevalence of COVID-19, infection fatality rates, and information on asymptomatic infections of SARS-CoV-2 among Canadian adults. Ab-C evolved with the pandemic, collecting vaccination and long COVID data, and later supplementing the original study population with more participants from vulnerable groups. <br>

<b>Methods:</b> Using Angus Reid Forum members as a sampling frame, 44,022 adults (18+ years) from across Canada were sampled, with demographic stratification, and invited to enroll. Phase I (May-Sept 2020) included a baseline questionnaire (self-administered webform) and an invitation to consent to receive a dried blood spot home sampling kit to test SARS-CoV-2 serology. Between Jan and Mar 2021, the first DBS samples were received concurrently with administration of second questionnaires. Phase 3 questionnaires and DBS samples were collected between Jun and Oct 2021. Phase 4 questionnaires were administered in Dec 2021 and again in Feb-March 2022, and the study population was supplemented with Forum members from racial minorities or having high-risk conditions (VIP). Phase 4 DBS samples were received between Jan and March 2022. In Summer 2022, a final Phase 5 included participants who had at least one prior serology result. They were invited to complete a questionnaire and provide a DBS collection. In summary, questionnaire data was collected approximately every 6 months between Fall 2020 and Summer 2022. DBS were collected in a subset of participants approximately every 6 months between Jan 2021 and July 2022. Questionnaires included the CITF Core Data Elements (or similar items) and additional question blocks for high priority contemporaneous pandemic issues such as mental health and long covid. <br>

<b>Contributed dataset contents:</b> The datasets include 20,343 participants who completed baseline questionnaires between May and Sept 2020. In Phase 4 Dec 2021, the sample was supplemented with 2681 participants from racial minorities or having high-risk conditions. Overall, 8633 participants have at least one SARS-CoV-2 serology result (from DBS received by lab between Jan 2021 and Aug 2022). About 5,600 participants provided longitudinal data with at least two serology results and two questionnaires. Questionnaire variables include data in the following areas of information: demographics (age, gender, race-ethnicity and indigeneity, province, education, household composition, occupations), general health (tobacco use; chronic conditions; height and weight; flu vaccine), COVID infection test results, symptoms and exposure risks, SARS-CoV-2 vaccination.