Cohort Profile: Prospective Cohort to Study the COVID-19 Immune Response in Retail Workers in Québec, Canada (CISACOV)
Authors: Santerre Kim , Thériault Mathieu , Brousseau Nicholas , Rochette Samuel , Pelletier Joelle N. , Gilbert Caroline , Masson Jean-François , Baz Mariana , Boudreau Denis , Trottier Sylvie 
Published: August 2023

ABSTRACTPurposeRetail workers are an understudied occupational group that may have been at increased risk of contracting SARS-CoV-2 during the COVID-19 pandemic. Therefore, we set up a longitudinal cohort of participants working in this sector to better document the incidence of SARS-CoV-2 infection and the immune response to infection and/or vaccination in this group.ParticipantsA total of 304 participants were recruited between April 20, 2021 and October 22, 2021. They were invited to attend three visits (each separated by ∼12 weeks) during which they provided blood samples and information on participant characteristics, COVID-19 symptoms, and vaccination. An extension phase of two additional visits was carried out between March 15th, 2022 and October 3rd, 2022 to document the impact of the Omicron variant among the 198 participants who were still eligible for recruitment. Participants were aged 18 to 75 and worked in grocery stores, hardware stores, bars or restaurants within the Québec City metropolitan area (Canada).Findings to date:This article describes participants’ demographic, socioeconomic, behavioral, clinical and occupational characteristics, and their COVID-19 symptoms (where applicable). It also describes SARS-CoV-2 vaccination status and any SARS-CoV-2 diagnostic test (i.e., PCR or rapid antigen) performed from the beginning of the pandemic until the last visit.Future plansThe incidence of SARS-CoV-2 infections will be assessed. The immune response (innate and acquired) to SARS-CoV-2 infection or vaccination will be studied using a variety of techniques, including reference and experimental enzyme-linked immunosorbent assays, microneutralization assays with live viruses, experimental pseudoneutralization with an angiotensin-converting enzyme 2-spike assay, peripheral blood mononuclear cells and neutrophil stimulation, and a proliferation assay based on carboxyfluorescein diacetate succinimidyl ester.RegistrationNot applicable.Strengths and limitationsThis cohort offers a comprehensive dataset to study the immune response to SARS-CoV-2 infection or vaccination (alone), or hybrid immunity, as participants provided information on a wide range of demographic, socioeconomic, behavioral, clinical, and occupational variables. However, the low proportion of racial minorities (i.e., 3.0%) limits the use of this cohort to study racial determinants of immunity to SARS-CoV-2.This cohort focuses on workers in the food and retail service sector, an understudied population at high risk of occupational exposure to infectious agents.This study covered seven pandemic waves and thus captured a large number of confirmed infections from different variants.Sample collection was initiated immediately prior to COVID-19 vaccine availability for this population and thus captured successive vaccination campaigns over 17 months.In keeping with the study design, none of the participants had severe COVID-19 disease requiring hospitalization at baseline, and none of the COVID-19 illnesses that occurred during the study required hospitalization; this cohort may not, therefore, be used to study the immune response leading to severe health outcomes, but is appropriate to study the immune response to mild SARS-CoV-2 infections.Nearly 1300 blood samples were collected; furthermore, only 13 out of 304 (4.3%) participants withdrew before attending all three initial visits, and 4 out of 198 (2.0%) participants who remained eligible in the extension phase withdrew before attending the fifth visit. A series of at least 5 blood samples drawn over 48 weeks is therefore available for most participants.