Longitudinal Evaluation of mRNA Vaccinated Subjects using a Quidel Multianalyte Point-of-Care SARS-CoV-2 IgG Immunoassay

Infection from SARS-CoV-2 elicits an immune response to the nucleocapsid (N) and spike proteins (subunits S1 and S2). In this study, we set out to understand the utility of the multiplexed Quidel Sofia 2 SARS-CoV-2 IgG Antibody Fluorescent Immuno-Assay (FIA) that measures IgG antibodies against these three primary SARS-CoV-2 antigens from a single sample in 15 minutes. Using this assay with samples that were collected prior to the COVID-19 pandemic (n=816) and diseased state samples (n=99), the specificities for the three antigens were 98.4-99.9% and 98.0-100.0%, respectively. A longitudinal study was designed to collect weekly fingerstick, venous whole blood, serum and plasma samples from subjects vaccinated with the Moderna or Pfizer/BioNtech mRNA vaccines. The majority of these enrolled subjects had no known prior infection while a subset was known to have had prior COVID-19 infection. We found that the fingerstick whole blood samples performed as effectively as serum, plasma, and venous whole blood samples with a 95.8-99.5% agreement allowing physicians in a near-patient setting to rapidly provide results to their patients. Additionally, as this assay measures an IgG response against three viral proteins, S1, S2 and N, we were able to characterize immune response between i) naturally infected subjects, ii) vaccinated subjects with no prior infection, iii) vaccinated subjects with known prior infection, and iv) vaccinated subjects with prior asymptomatic exposure/infection. The Quidel Sofia 2 SARS-CoV-2 IgG FIA will aid in providing insights to the protective humoral responses as an increasing number of the world population is vaccinated against SARS-CoV-2.