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

Asamoah-Boaheng M., Goldfarb D. M., Karim M. E., O’Brien S. F., Wall N., Drews S. J., Barakauskas J., Jassem A. N., Grunau B. The relationship between anti-spike SARS-CoV-2 antibody levels and risk of breakthrough COVID-19 among fully vaccinated adults. The Journal of Infectious Diseases. 2022. Doi: 10.1093/infdis/jiac403.

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

A study published in The Journal of Infectious Diseases by CITF-funded researchers Drs. Brian Grunau, David Goldfarb, and Agatha Jassem (University of British Columbia), and Sheila O’Brien and Steven Drews (both from Canadian Blood Services) shows that higher antibody levels against the original (wild-type) SARS-CoV-2 virus are associated with a significantly reduced risk of subsequent infections with SARS-CoV-2 variants, both preceding and during the Omicron era. The association, however, was weaker during the Omicron wave.

Key findings:

  • Modelling shows that during the pre-Omicron era, an increase in the total anti-spike antibody concentration was associated with a 34% reduced risk of a subsequent COVID-19 diagnosis. Similarly, an increase in anti-spike and anti-RBD IgG concentration was associated with a 35% and 37% reduced risk of COVID-19, respectively.
  • Similarly, modeling shows that during the Omicron era, an increase in the total anti-spike antibody concentration was associated with a 17% reduced risk of subsequent COVID-19 diagnosis. an increase in anti-spike and anti-RBD IgG concentrations was associated with a 20% and 21% reduced risk of COVID-19, respectively
  • Vaccine-induced antibody levels were also found to be higher in Omicron-era samples, which could be explained by the high uptake of the third vaccine dose (70% of the cohort). These high antibody levels resulted in a weaker reduced risk of COVID-19 diagnosis. That said, there was a higher incidence of COVID-19 during this period, likely explained, according to the authors, by the waning of antibodies after vaccination.

While this study does show a relationship between antibody levels and COVID-19 risks, the exact nature of that relationship is complicated. In particular, it remains unclear to what extent waning of these vaccine-induced antibodies, which is now a well-known phenomenon, is responsible for the increase in the number of infections, as observed since the emergence of the Omicron variant. The high variability between patients is also to be considered when assessing immune protection.

Samples for this study were taken from the CITF-funded COVID-19 Occupational Risks, Seroprevalence and Immunity among Paramedics in Canada (CORSIP) study. Adult paramedics who received at least two doses of COVID-19 vaccines and did not have COVID-19 prior to blood collection were included. The study distinguishes between pre-Omicron era cases (those diagnosed before November 30, 2021) and Omicron era cases (those diagnosed between December 26, 2021 and March 31, 2022). A total of 523 and 579 adult participants were included in the pre-Omicron and Omicron cohorts, respectively.