Predictors of SARS-CoV-2 anti-Spike IgG antibody levels following two COVID-19 vaccine doses among children and adults in the Canadian CHILD Cohort (preprint)

Background: Vaccination helps prevent SARS-CoV-2 infection and severe COVID-19. However, vaccine-induced humoral immune responses vary among individuals and wane over time. We aimed to describe the SARS-CoV-2 anti-spike IgG antibody response to vaccination and identify health and demographic factors associated with this response among children and adults. Methods: We studied a subset of double-vaccinated children (n= 151; mean age: 12 {+/-}1.5 years, 46% female) and adults (n= 995; 44 {+/-}6.0 years, 60% female) from the Canadian CHILD Cohort. Dried blood spots were collected over two time periods (March 2021 to September 2021; October 2021 to January 2022). Antibody levels were quantified using automated chemiluminescent ELISAs. Demographic, vaccination, and health data were collected via online questionnaires. Associations were determined using multivariable regression. Results: Our cohort had SARS-CoV-2 anti-spike seropositivity rate of 97% following two COVID-19 vaccine doses. In both children and adults, the highest antibody levels were observed around three months post-vaccination and did not differ by biological sex. Higher antibody levels were associated with: prior SARS-CoV-2 infection ({beta}=0.15 scaled luminescence units, 95%CI, 0.06-0.24), age <18 years ({beta}=0.15, 95%CI 0.05-0.26) and receiving the Moderna mRNA ({beta}=0.23, 95%CI 0.11-0.34) or Pfizer-BioNTech mRNA vaccines ({beta}= 0.10, 95%CI, 0.02-0.18) vs. a combination of mRNA and Oxford-AstraZeneca viral vector vaccines. There were no differences in antibody levels when comparing a 3-8 vs. 9-16-week interval between vaccine doses. Interpretation: We identified key factors associated with post-vaccination antibody responses in children and adults, which could help improve future vaccine development and deployment among different population subgroups.

Investigating SARS-CoV-2 infection and the health and psychosocial impact of the COVID-19 pandemic in the Canadian CHILD Cohort study: methodology and cohort profile (preprint)

Background: The COVID-19 pandemic is affecting all Canadian families, with some impacted differently than others. Our study aims to: 1) determine the prevalence and transmission of SARS-CoV-2 infection among Canadian families, 2) identify predictors of infection susceptibility and severity of SARS-CoV-2 and 3) identify health and psychosocial impacts of the COVID-19 pandemic. Methods: This study builds upon the CHILD Cohort Study, an ongoing multi-ethnic general population prospective cohort consisting of 3454 Canadian families with children born in Vancouver, Edmonton, Manitoba, and Toronto between 2009-12. During the pandemic, 1462 CHILD households (5378 individuals) consented to participate in the CHILD COVID-19 Add-On Study involving: (1) brief biweekly surveys about COVID-19 symptoms and testing; (2) quarterly questionnaires assessing COVID-19 exposure, testing and vaccination status, physical and mental health, and pandemic-driven life changes; (3) in-home biological sampling kits to collect blood and stool. Mean ages were 9 years (range 0-17) for children and 43 years (range 18-85) for adults. Prevalence of SARS-CoV-2 infection will be estimated from survey data and confirmed through serology testing. We will combine these new data with a wealth of pre-pandemic CHILD data and use multivariate modelling and machine learning methods to identify risk and resilience factors for susceptibility and severity to the direct and indirect effects of the pandemic. Interpretation: Our short-term findings will inform key stakeholders and knowledge users to shape current and future pandemic responses. Additionally, this study provides a unique resource to study the long-term impacts of the pandemic as the CHILD Cohort Study continues.