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

Huynh A, Arnold DM, Smith JW, Moore JC, Zhang A, Chagla Z, Harvey BJ, Stacey HD, Ang JC, Clare R, Ivetic N, Chetty VT, Bowdish DME, Miller MS, Kelton JG, Nazy I. Characteristics of anti-SARS-CoV-2 antibodies in recovered COVID-19 subjects. Viruses. 2021 Apr 16;13(4):697. doi: 10.3390/v13040697.

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

In a recent publication in Viruses, Dr. Ishac Nazy from McMaster University finds that SARS-CoV-2 antibodies against the spike and receptor binding domain are present for at least six months, confirming similar research by other CITF-funded researchers. In this publication, Dr. Nazy characterizes SARS-CoV-2 antibodies in recovered COVID-19 patients. This study was funded in part by the COVID-19 Immunity Task Force, in collaboration with the Canadian Institutes of Health Research (CIHR).


Main conclusions:

  • Antibodies against the SARS-CoV-2 spike (S) and receptor-binding domain (RBD) were present in the majority of recovered subjects for at least six months.
  • SARS-CoV-2 S protein and RBD IgG correlated with high levels of neutralizing antibodies.


The study recruited 153 individuals with positive SARS-CoV-2 RT-PCR who had since recovered, along with 55 individuals who tested negative by RT-PCR, from hospitals in Hamilton, Ontario. In this cross-sectional study, blood samples were collected from recovered patients at different time points.

Using an enzyme-linked immunosorbent assay (ELISA), SARS-CoV-2 immunoglobulin IgG, IgA, and IgM antibodies against spike (S) protein and its receptor-binding domain (RBD) were present in 85.6% of all 153 recovered subjects. At 60 to 120 days post-symptom onset, SARS-CoV-2 S IgG was still found in all recovered subjects tested at this time point (n=23). Within the 120- to 180-day interval, 91.7% (n=60) of recovered individuals tested at this time point had SARS-CoV-2 S protein IgG detected. Beyond 180 days, 90.9% of those tested (n=11) had this antibody, although antibodies slightly declined. The same trend was observed for IgG levels against RBD, where over the course of 180 days, the number of individuals with these antibodies slightly declined.

In contrast, the kinetics for IgA and IgM were quite different. SARS-CoV-2 IgA and IgM against the S and RBD levels reached the maximum between 0 to 60 days post-symptom onset and decreased noticeably over time. After 180 days, SARS-CoV-2 S protein and RBD IgA levels declined by 30% and 80%, respectively, while IgM levels for both antigens declined by 90%. These trends are consistent with CITF-funded research led by Dr. Andrés Finzi from Université de Montréal and Dr. Renée Bazin from Héma Québec concluding that IgM and IgA decreased much faster than IgG.

The abilities of these antibodies to neutralize the live SARS-CoV-2 virus were also assessed. Both high levels of SARS-CoV-2 S protein and RBD IgG correlated with high levels of neutralizing antibodiesAntibodies that bind to the surface structures of a pathogen, preventing it from entering and infecting its host cells. These neutralizing antibodies were also detected as far out as 180 days post-symptom onset.

The authors highlight that most recovered COVID-19 individuals have antibody responses that last at least six months. These results support findings from papers published in Science and Emerging Infectious Diseases as well as Drs. Daniel Kaufmann and Andrés Finzi’s research where they found memory B cells and antibodies persisting for at least eight months.