Cross-sectional Characterization of SARS-CoV-2 Antibody Levels and Decay Rates Following Infection of Unvaccinated Elderly Individuals

Marilyn Whelan; Yannick Galipeau; Nicole White-Al Habeeb; Danijela Konforte; Mohamed Abou El Hassan; Ronald A Booth; Corey Arnold; Marc-André Langlois; Martin Pelchat

doi:10.1093/ofid/ofad384

Cross-sectional Characterization of SARS-CoV-2 Antibody Levels and Decay Rates Following Infection of Unvaccinated Elderly Individuals

Open Forum Infect Dis. 2023 Jul 20;10(8):ofad384. doi: 10.1093/ofid/ofad384. eCollection 2023 Aug.

Authors

Affiliations

¹ Department of Biochemistry, Microbiology and Immunology, Faculty of Medicine, University of Ottawa, Ottawa, Canada.
² Dynacare, Brampton, Canada.
³ LifeLabs Medical Laboratory Services, Etobicoke, Canada.
⁴ Department of Pathology, Dalhousie University, Halifax, Canada.
⁵ Department of Pathology and Laboratory Medicine and the Eastern Ontario Regional Laboratory Association, University of Ottawa and The Ottawa Hospital, Ottawa, Canada.
⁶ Centre for Infection, Immunity and Inflammation, University of Ottawa, Ottawa, Canada.

Abstract

Background: SARS-CoV-2 infections have disproportionally burdened elderly populations with excessive mortality. While several contributing factors exists, questions remain about the quality and duration of humoral antibody-mediated responses resulting from infections in unvaccinated elderly individuals.

Methods: Residual serum/plasma samples were collected from individuals undergoing routine SARS-CoV-2 polymerase chain reaction testing in a community laboratory in Canada. The samples were collected in 2020, before vaccines became available. IgG, IgA, and IgM antibodies against SARS-CoV-2 nucleocapsid, trimeric spike, and its receptor-binding domain were quantified via a high-throughput chemiluminescent enzyme-linked immunosorbent assay. Neutralization efficiency was also quantified through a surrogate high-throughput protein-based neutralization assay.

Results: This study analyzed SARS-CoV-2 antibody levels in a large cross-sectional cohort (N = 739), enriched for elderly individuals (median age, 82 years; 75% >65 years old), where 72% of samples tested positive for SARS-CoV-2 by polymerase chain reaction. The age group ≥90 years had higher levels of antibodies than that <65 years. Neutralization efficiency showed an age-dependent trend, where older persons had higher levels of neutralizing antibodies. Antibodies targeting the nucleocapsid had the fastest decline. IgG antibodies targeting the receptor-binding domain remained stable over time, potentially explaining the lack of neutralization decay observed in this cohort.

Conclusions: Despite older individuals having the highest levels of antibodies postinfection, they are the cohort in which antibody decay was the fastest. Until a better understanding of correlates of protection is acquired, along with the protective role of nonneutralizing antibodies, booster vaccinations remain important in this demographic.

Keywords: COVID-19; SARS-CoV-2; elderly; neutralization; serology.