ABSTRACT
Background-aim: Monitoring immune protection post-administration of an mRNA SARS-CoV-2 vaccine is essential to inform public health policy. The potential utility of quantitative antibody assays to indicate risk of breakthrough infection is of interest. Significant evidence gaps exist in our understanding of antibody response in children and adolescents relative to adults post-vaccination. The current study aims to evaluate age-specific differences in antibody response to SARS-CoV-2 vaccination in a large cohort of Canadian children, adolescents, and adults. Methods: Quantitative serological antibody response following administration of one, two, or three doses of an mRNA SARS-CoV-2 vaccine were evaluated in a prospective cohort of 454 participants (age range: 6-79y, male: 34%, female: 66%). A subset of participants were longitudinally monitored during a five month period (Aug–Dec 2021). A control cohort of individuals with no history of SARS-CoV-2 infection or vaccination were evaluated to assess specificity. Antibody levels were measured using two immunoassays: DiaSorin LIAISON SARS-CoV-2 TrimericS IgG and Abbott AdviseDx SARS-CoV-2 IgG II assays. Results: Antibody assay sensitivity in study participants post-second and third dose were 96% and 98%, respectively. Antibody titres varied significantly depending on days since vaccine administration. Participants post-third dose reached maximum titres of 25,000 BAU/mL and ten-fold relative increase in longitudinal cohort. A statistically significant difference was observed between pediatric (mean±SD= 2037±1515) and adult 1444±1277) antibody titres. A specificity of 98% was observed for participants with no history of SARS-CoV-2 infection or vaccination. A strong correlation between titres on the AdviseDx and TrimericS assays were observed (Pearson R: 0.92). Conclusions: This is the largest evaluation of commercially available quantitative SARS-CoV-2 antibody assays in a cohort of Canadian children, adolescents, and adults. Findings suggest children have higher antibody titres as compared to adults post-administration of an mRNA vaccine. However, significant variation was observed. Future work is needed to relate antibody presence to functional immune response as well as risk of breakthrough infections.