biostudies-literatureGaultier GNBC Children's Hospital Research InstituteBC Children’s Hospital Bertram Hoffmeister Postdoctoral Fellowship AwardCystic Fibrosis Foundation and Cystic Fibrosis CanadaBC Children’s Hospital FoundationPublic Health Agency of Canada, through the Vaccine Surveillance Reference Group and the COVID-19 Immunity Task ForceMichael Smith Foundation for Health ResearchCanadian Immunization Research Network Post-doctoral Fellowship AwardPublic Health Agency of Canada, BC Immunization CommitteeCanadian Immunization Research Network Doctoral Award8926https://www.ebi.ac.uk/biostudies/studies/S-EPMC11026432biostudies-literatureUnknown14(1)To evaluate immune responses to COVID-19 vaccines in adults aged 50 years and older, spike protein (S)-specific antibody concentration, avidity, and function (via angiotensin-converting enzyme 2 (ACE2) inhibition surrogate neutralization and antibody dependent cellular phagocytosis (ADCP)), as well as S-specific T cells were quantified via activation induced marker (AIM) assay in response to two-dose series. Eighty-four adults were vaccinated with either: mRNA/mRNA (mRNA-1273 and/or BNT162b2); ChAdOx1-S/mRNA; or ChAdOx1-S/ChAdOx1-S. Anti-S IgG concentrations, ADCP scores and ACE2 inhibiting antibody concentrations were highest at one-month post-second dose and declined by four-months post-second dose for all groups. mRNA/mRNA and ChAdOx1-S/mRNA schedules had significantly higher antibody responses than ChAdOx1-S/ChAdOx1-S. CD8⁺ T-cell responses one-month post-second dose were associated with increased ACE2 surrogate neutralization. Antibody avidity (total relative avidity index) did not change between one-month and four-months post-second dose and did not significantly differ between groups by four-months post-second dose. In determining COVID-19 correlates of protection, a measure that considers both antibody concentration and avidity should be considered.Scientific reportsAdaptive immune responses to two-dose COVID-19 vaccine series in healthy Canadian adults ≥ 50 years: a prospective, observational cohort study.PMC11026432AWD-0180412122-HQ-000218McMillan BZlosnik JEASkowronski DMSimmons KLevings MKKrajden MJassem ANPoloni CSadarangani MCai BCook LMarquez ACSteiner TLo MMorshed MShulha HPZheng JJSekirov IBartlett SRBaer HMGaultier GNfalseAdaptive immune responses to two-dose COVID-19 vaccine series in healthy Canadian adults ≥ 50 years: a prospective, observational cohort study.To evaluate immune responses to COVID-19 vaccines in adults aged 50 years and older, spike protein (S)-specific antibody concentration, avidity, and function (via angiotensin-converting enzyme 2 (ACE2) inhibition surrogate neutralization and antibody dependent cellular phagocytosis (ADCP)), as well as S-specific T cells were quantified via activation induced marker (AIM) assay in response to two-dose series. Eighty-four adults were vaccinated with either: mRNA/mRNA (mRNA-1273 and/or BNT162b2); ChAdOx1-S/mRNA; or ChAdOx1-S/ChAdOx1-S. Anti-S IgG concentrations, ADCP scores and ACE2 inhibiting antibody concentrations were highest at one-month post-second dose and declined by four-months post-second dose for all groups. mRNA/mRNA and ChAdOx1-S/mRNA schedules had significantly higher antibody responses than ChAdOx1-S/ChAdOx1-S. CD8⁺ T-cell responses one-month post-second dose were associated with increased ACE2 surrogate neutralization. Antibody avidity (total relative avidity index) did not change between one-month and four-months post-second dose and did not significantly differ between groups by four-months post-second dose. In determining COVID-19 correlates of protection, a measure that considers both antibody concentration and avidity should be considered.2024-01-01T00:00:00Z2024 Apr2026-05-29T12:21:55.428Z2026-05-19T03:07:25.979ZS-EPMC110264323863755810.1038/s41598-024-59535-0