ABSTRACT
Background: Quantifying antibody reactivity to SARS-CoV-2 antigens may help understand its effect on COVID-19 severity at the population level. This antibody 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. A novel 10-plex antibody assay (IgG) was used to measure antibody reactivity against the spike protein from circulating coronaviruses (229E, NL63, OC43, and HKU1), SARS-CoV, and four SARS-CoV-2 antigens. Seroreactivity from previous viral exposure was ascertained using this assay, and by measuring total SARS-CoV-2 IgG/M/A antibodies against a recombinant spike (S1) protein using a commercial CLIA assay. Findings: Among 276 participants (71% HCW), three showed evidence of direct viral exposure, yielding an adjusted seroprevalence of 0.6% [95%CI 0.2 to 3.1%], 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% to 11.1%], 48.7 [95%CI 42.7% to 54.8%] and 82.4% [95%CI 77.4% to 86.7%] showed antibody reactivity against SARS-CoV-2 RBD, N or Spike proteins, respectively. This reactivity was evenly distributed as a function of age, sex or between paediatric and adult HCW, and partly correlated with reactivity to circulating coronaviruses (Spearman; range: 0.147 to 0.513 for significant correlation after false-discovery rate adjustment at 5%). Interpretation: A substantial proportion of individuals in this population showed antibody reactivity against SARS-CoV-2 antigens despite low serological evidence of SARS-CoV-2 exposure.