Antibody Reactivity Against SARS-CoV-2 in Adults from the Vancouver Metropolitan Area, Canada

Background: Quantifying antibody reactivity against multiple SARS-CoV-2 antigens at the population level may help understand individual differences in COVID-19 severity. Pre-existing low antibody cross-reactivity may be particularly prevalent among childcare providers, including pediatric health care workers (HCW) who may be more exposed to circulating coronaviruses. Methods: Cross-sectional study that included adults in the Vancouver area in British Columbia (BC), Canada, between May 17 and June 19, 2020. SARS-CoV-2 seroprevalence was ascertained by measuring total SARS-CoV-2 IgG/M/A antibodies against a recombinant spike (S1) protein, and adjusted for bias due to false-positive and false-negative test results. A novel, high sensitivity multiplex assay was also used to profile IgGs against four SARS-CoV-2 antigens, SARS-CoV and four circulating coronaviruses. Findings: Among 276 participants (71% HCW), three showed evidence of direct viral exposure, yielding an adjusted seroprevalence of 0.60% [95%CI 0% - 2.71%], with no difference between HCW and non-HCW, or between paediatric and adult HCW. Among the remaining 273 unexposed individuals, 7.3% [95%CI 4.5% - 11.1%], 48.7 [95%CI 42.7% - 54.8%] and 82.4% [95%CI 77.4% - 86.7%] showed antibody reactivity against SARS-CoV-2 RBD, N or Spike proteins, respectively. SARS-CoV-2 reactivity did not correlate with age, sex, did not differ between HCW and non-HCW (prevalence: 1.0% vs 1.0%; P=1.00) and between pediatric and adult HCW (prevalence: 0.7% vs 1.6%; P=0.54), and weakly correlated with reactivity to circulating coronaviruses (Spearman rho range: 0.130 to 0.224 for 7 significant out of 16 correlations; false-discovery rate-adjusted for a total of 36 correlations). Interpretation: A substantial proportion of individuals showed low, but detectable antibody reactivity against SARS-CoV-2 antigens in this population despite a low evidence of direct SARS-CoV-2 exposure.