Fully Quantitative Measurements of the Antibody Levels for SARS-CoV-2 Infections and Vaccinations calibrated against the NISTmAb Standard IgG Antibody

Abstract

Humanised recombinant antibodies specific to the SARS-CoV-2 Spike protein were calibrated against the NISTmAb standard human antibody to produce a fully quantitative antibody assay. The assay allows comparative studies between patient cohorts to be performed from which common properties may be derived. Two cohorts comparing patient vaccine response to AstraZeneca ChAdOx1-S (AZ, 35 patients) and Pfizer/BioNTech BNT162b2 (Pfizer, 25 patients) shows close association of the 31st percentile of the AZ distribution (2.90 ± 1.10 mg/L) and the 7th percentile of the Pfizer distribution (1.11 ± 1.10 mg/L) corresponding to the efficacy of the vaccines at preventing infection. The AZ IgG response distribution varies from 0.6 mg/L-25.4 mg/L with an average (mode) of 3.3 ± 1.0 mg/L; the Pfizer response distribution varies from 0.6 mg/L to 33.1 mg/L with a mode of 3.7 ± 1.0 mg/L. A third patient cohort looked at the recovery of 195 SARS-CoV-2 RT-PCR-positive patient samples and 200 pre-pandemic patient samples. A fourth patient cohort reviewed the NIBSC Anti-SARS-CoV-2 Verification Panel. The diagnostic cut-off for RT-PCR-positive patient samples was 1.34 ± 1.10 mg/L and the NIBSC panel separated seropositive and seronegative samples at 1.90 ± 1.10 mg/L. The mean value of the two prevention and two recovery thresholds is 1.8 mg/L with 95% confidence limits of 0.2-3.4 mg/L. In recovery and, critically, infection prevention, an antibody concentration threshold estimate of 3.4 mg/L appears mechanistically important. An antibody immunity threshold predicting a mucosal concentration preventing SARS-CoV-2 colonisation of the nasopharyngeal cavity is discussed.

Vaccine, Booster and Natural Antibody Binding to SARS-CoV-2 Omicron (BA.1) Spike Protein and Vaccine Efficacy

“…The integrity of the mono calibration epitope on the S2 region has degraded, with an estimated affinity of 0.36 nM and 8.0 nM to the SO variant. The integrity of the 3-pt calibration for quantification is maintained 6 for both the S and SO assays using the same antibody. The antibody response distributions from the three patient cohorts for both the S and SO proteins are shown in Figure 1, demonstrating that the booster response ranges from 0.5 mg/L -100 mg/L for the S protein and 0.5 mg/L -140 mg/L for the SO protein.…”

“…The mucosal immunity threshold 6 is set at 3.4 mg/L and was derived from experimental distribution function describing the antibody responses of double-vaccinated patients (AZ n = 35, Pfizer n = 25). The reported vaccine efficacies at stopping infection were AZ 69% and Pfizer 93%.…”

“…The immuno-kinetic assay uses a biophotonic detection event and has been described in detail elsewhere in a SARS-CoV-2 antibody sensing application 6,9 . Briefly, light excites a plasmon wave in the free electrons of gold nanoparticles, which then scatter light.…”

“…Commercial samples Commercial samples purchased from two suppliers (Biomex GmbH and AbBaltis) have previously been used to determine the clinical threshold for the Triple Antibody Test. 6 A small subset of these were used to assess the antibody response profile following natural infection. All samples tested were found negative for STS, HBsAg, HIV1 Ag (or HIV PCR(NAT)), HIV1/2 antibody, HCV antibody and HCV PCR(NAT) by FDA approved tests; all samples were from RT-PCR positive (PCR+) individuals: 9 samples were purchased from AbBaltis (44% from male donors and 56% from female donors) and 23 were purchased from Biomex (65% from male donors and 35% from female donors).…”

“…Recently, we proposed an antibody mucosal immunity threshold that may be protective against infection based on the concentration of antibodies in the mucosa preventing entrance of the viral particles into the epithelium cells 6 . Concentrations of neutralising and opsonising antibodies in the mucosa may be more than 10 11 above every mm -2 derived from a serum concentration of 1.8 mg/L (95% confidence intervals of 0.2 mg/L – 3.4 mg/L).…”