>>14070868https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciab465/6279075>Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) proteins were measured in longitudinal plasma samples collected from 13 participants who received two doses of mRNA-1273 vaccine. Eleven of 13 participants showed detectable levels of SARS-CoV-2 protein as early as day 1 after first vaccine injection. Clearance of detectable SARS-CoV-2 protein correlated with production of immunoglobulin G (IgG) and immunoglobulin A (IgA).>The mean spike peak level was 62 pg/mL±13 pg/mL.https://www.medrxiv.org/content/10.1101/2020.07.20.20156372v1.full.pdfTo probe for the presence of viral antigens in plasma, we tested samples from COVID-19
20 positive patients using our SARS-CoV-2 Simoa antigen assays for S1, spike, and N. These patients
were determined to be COVID-19 positive by NP RT-PCR and all plasma samples were obtained
within the first ten days of the initial NP RT-PCR test. Both S1 and N were detected in 41 of 64
COVID-19 positive patients (Fig. 1b and 1c), who we identify as “viral antigen positive.” We
observe S1 and N concentrations spanning four orders of magnitude in these plasma samples.
25 Despite the presence of S1 and N in some samples, spike was only detectable in 5 of 64 COVID19 positive patients (Fig. S4). Spike may be undetectable in some samples since the LOD is one
order of magnitude higher than the LOD of the S1 assay. Additionally, in the Simoa assay for
spike, the formation of a full immunocomplex depends on spike binding to the S2 subunit capture
beads and the S1 subunit detection antibody. Therefore, we hypothesize that free spike antigen in
30 plasma is likely proteolytically cleaved, releasing the S1 subunit, and the remaining spike protein
fragment is undetectable by our assay.