This is a summary, written by members of the CITF Secretariat, of:

Cherry N, Adisesh A, Burstyn I, Charlton C, Chen Y, Durand-Moreau Q, Labrèche F, Ruzycki S, Turnbull L, Zadunayski T, Yasui Y. Determinants of SARS-CoV-2 IgG response and decay in Canadian healthcare workers: a prospective cohort study. medRxiv.2023Sept13. doi:

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

A CITF-funded study among Canadian healthcare workers, published in preprint and not yet peer-reviewed, found that SARS-CoV-2 anti-receptor binding domain (RBD) IgG levels increased following each COVID-19 vaccine dose and after the first SARS-CoV-2 infection. However, SARS-CoV-2 anti-RBD IgG levels decreased over time, with the sharpest decline observed after the third vaccine dose. This study was led by Dr. Nicola Cherry (University of Alberta).

Key findings:

  • With each COVID-19 vaccine dose, the levels of SARS-CoV-2 anti-receptor binding domain (RBD) IgG increased, but levels waned over time, most steeply after the third vaccine dose.
  • Participants who received the mRNA-1273 (Moderna) vaccine had higher SARS-CoV-2 anti-RBD IgG levels than those who received the Pfizer-BioNTech vaccine.
  • Participants with conditions such as multiple sclerosis and rheumatoid arthritis, as well as those taking certain immunosuppressive medications, tumor necrosis factor inhibitors, calcineurin inhibitors, and antineoplastic agents, had lower anti-RBD IgG levels.
  • Participants who reported more side effects after vaccination had a stronger anti-RBD IgG response.
  • Women whose vaccination was early in pregnancy had a weaker anti-RBD response.

Through serial blood sampling and a longitudinal analysis, this study led to a better understanding of how people respond to COVID-19 vaccines and infections over time, highlighting the importance of tailored vaccination strategies.

Healthcare workers (HCW) were recruited from Alberta, British Columbia, Ontario, and Quebec between April to October 2020. They provided blood samples four months after their initial SARS-CoV-2 immunization and then at seven, ten, and 13 months to analyze SARS-CoV-2 anti-RBD IgG and anti-nucleocapsid IgG antibody levels: 2752 HCWs donated at least one sample. The data also included information on the type and timing of immunizations, SARS-CoV-2 infection history, immunologically-compromising conditions, and medications.