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.

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 cross-provincial 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 (e.g. location, age, ethnicity, prior SARS-CoV-2 infection, vaccine type, comorbidities) were collected via online questionnaires. Associations were tested using multivariable linear mixed-effect analysis accounting for household membership.

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 (β = 0.16 scaled luminescence units; 95%CI 0.07,0.25), age < 18 years (13-17 years old, β = 0.14; 95%CI 0.03,0.25 | <13 years old: β = 0.17; 95%CI 0.03,0.32) and receiving mRNA vaccines (two Moderna: β = 0.21; 95%CI 0.10,0.33 | two Pfizer-BioNTech (β = 0.10; 95%CI 0.02,0.18 | one Modern and one Pfizer-BioNTech β = 0.14; 95%CI 0.01,0.27) vs. receiving Oxford-AstraZeneca viral vector vaccines. There were no antibody level differences among study sites, ethnicities, household essential worker status, education levels, immunosuppressive comorbidity presence, or when comparing a 3-8 vs. 9-16-week interval between vaccine doses.

INTERPRETATION: We identified key factors (i.e. prior SARS-CoV-2 infection, age, vaccine type) associated with post-vaccination antibody responses in children and adults across Canada. This may help improve future vaccine development and deployment among different population subgroups.