We developed novel assays to characterize the immune response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, at a time when the COVID-19 pandemic had just begun and serological diagnostic tests did not exist. We developed a high-throughput enzyme-linked immunosorbent assay (ELISA) to detect anti-SARS-CoV-2 antibodies again the Spike protein and its receptor binding domain (RBD), and a viral neutralization assay to measure how well the antibodies can neutralize SARS-CoV-2 virus and prevent infection of host cells (Huynh A, Viruses 2021). This work provided a testing platform for COVID-19 serology to study patients who developed COVID-19 critical illness (Nazy, J Thomb Haem 2021), side effects from COVID-19 vaccines (Appelbaum J, Blood Advances 2022), and surveillance studies of vaccine responses among seniors living in nursing homes (Zhang A, J Am Med Dir Assoc 2022).

Anti-SARS-CoV-2 immunoglobulin (Ig)G/A/M antibodies against Spike protein and RBD were characterized by novel enzyme-linked immunosorbent assays (ELISA) in patient who had recovered from proven COVID-19 infection (n = 153) and negative controls (n = 55). We determined the ability of these antibodies to neutralize live SARS-CoV-2 virus. We found that anti-SARS-CoV-2 antibodies were detected in 90.9% of recovered subjects up to 180 days post-symptom onset. Anti-Spike antibody titers correlated with viral neutralization. Of the RT-PCR-positive subjects, 22 (14.3%) did not have anti-SARS-CoV-2 antibodies; raising the possibility that these indeterminate results were from individuals who were not infected (false-positives) or had mild infection only that failed to elicit an antibody response. This study highlighted the importance of serological surveys as a complementary tool to determine population-level immunity based on SARS-CoV-2 infection numbers determined by RT-PCR.

This allowed us to conduct serological studies to investigate patients with COVID-19 critical illness and patient with rare side effects from COVID-19 vaccines. In addition, this testing platform was used to characterize the immune response to vaccines among various populations. This work allowed us to leverage additional funding by the Ontario governments COVID-19 Rapid Research Fund and from the COVID-19 Immunity Task Force (CITF) to study the immunological response to SARS-CoV-2 infection. The assays developed in our laboratory continue to support collaborative studies with partners at McMaster University and McGill University to determine vaccine responses among some of the most vulnerable patients including residents of long-term care facilities and patients with inflammatory diseases receiving immune suppressive medications. Our work has informed policy on vaccination schedules for third and subsequent doses for the elderly, and will further characterize long term immune responses.

Huynh A, Arnold DM, Smith JW, Moore JC, Zhang A, Chagla Z, Harvey BJ, Stacey HD, Ang JC, Clare R, et al. Characteristics of Anti-SARS-CoV-2 Antibodies in Recovered COVID-19 Subjects. Viruses. 2021; 13(4):697. https://doi.org/10.3390/

Appelbaum J, Arnold DM, Kelton JG, Gernsheimer T, Jevtic SD, Ivetic N, Smith JW, Nazy I. SARS-CoV-2 spike-dependent platelet activation in COVID-19 vaccine-induced thrombocytopenia. Blood Adv. 2022 Apr 12;6(7):2250-2253. doi: 10.1182/bloodadvances.2021005050. PMID: 34724709; PMCID: PMC8563079.

Nazy I, Jevtic SD, Moore JC, Huynh A, Smith JW, Kelton JG, Arnold DM. Platelet-activating immune complexes identified in critically ill COVID-19 patients suspected of heparin-induced thrombocytopenia. J Thromb Haemost. 2021 May;19(5):1342-1347. doi: 10.1111/jth.15283. Epub 2021 Mar 14. PMID: 33639037; PMCID: PMC8014456.

Breznik JA, Zhang A, Huynh A, Miller MS, Nazy I, Bowdish DME, Costa AP. Antibody Responses 3-5 Months Post-Vaccination with mRNA-1273 or BNT163b2 in Nursing Home Residents. J Am Med Dir Assoc. 2021 Dec;22(12):2512-2514. doi: 10.1016/j.jamda.2021.10.001. Epub 2021 Nov 1. PMID: 34736891; PMCID: PMC8558841.

Zhang A, Breznik JA, Clare R, Nazy I, Miller MS, Bowdish DME, Costa AP. Antibody Responses to Third-Dose mRNA Vaccines in Nursing Home and Assisted Living Residents. J Am Med Dir Assoc. 2022 Mar;23(3):444-446. doi: 10.1016/j.jamda.2021.12.035. Epub 2022 Jan 15. PMID: 35041829; PMCID: PMC8760605.

Breznik JA, Huynh A, Zhang A, Bilaver L, Bhakta H, Stacey HD, Ang JC, Bramson JL, Nazy I, Miller MS, Denburg J, Costa AP, Bowdish DME; other members of the COVID-in-LTC Investigator Group. Cytomegalovirus Seropositivity in Older Adults Changes the T Cell Repertoire but Does Not Prevent Antibody or Cellular Responses to SARS-CoV-2 Vaccination. J Immunol. 2022 Nov 15;209(10):1892-1905. doi: 10.4049/jimmunol.2200369. PMID: 36426948; PMCID: PMC9666329.

Leong DP, Zhang A, Breznik JA, Clare R, Huynh A, Mushtaha M, Rangarajan S, Stacey H, Kim PY, Loeb M, Denburg JA, Mertz D, Chagla Z, Nazy I, Miller MS, Bowdish DME, Duong M. Comparison of three dosing intervals for the primary vaccination of the SARS-CoV-2 mRNA Vaccine (BNT162b2) on magnitude, neutralization capacity and durability of the humoral immune response in health care workers: A prospective cohort study. PLoS One. 2023 Feb 15;18(2):e0281673. doi: 10.1371/journal.pone.0281673. PMID: 36791069; PMCID: PMC9931154.