The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of Coronavirus Disease 2019 (COVID-19). While molecular-based testing is used to diagnose COVID-19, serologic testing of antibodies specific to SARS-CoV-2 is used to detect past infection. While most serologic assays are qualitative, a quantitative serologic assay was recently developed that measures antibodies against the S protein, the target of vaccines. Quantitative antibody determination may help determine antibody titer, facilitate longitudinal monitoring of the antibody response, including antibody response to vaccines. We evaluated the quantitative Roche Elecsys® Anti-SARS-CoV-2 S assay. Specimens from 167 PCR-positive patients and 103 control specimens were analyzed using the Elecsys® Anti-SARS-CoV-2 S assay on the cobas e411 (Roche Diagnostics). Analytical evaluation included assessing linearity, imprecision, and analytical sensitivity. Clinical evaluation included assessing clinical sensitivity, specificity, cross-reactivity, positive predictive value (PPV), negative predictive value (NPV), and serial sampling from the same patient. The Elecsys® Anti-SARS-CoV-2 S assay exhibited highest sensitivity of 84.0% 15-30 days post-PCR positivity, no cross-reactivity, specificity and PPV of 100%, and NPV between 98.3%-99.8% ≥14 days post-PCR positivity, depending on the seroprevalence estimate. Imprecision was <2% at 9.06 U/mL across 6 days, the negative QC was consistently negative (<0.40 U/mL), the manufacturer’s claimed limit of quantitation of 0.40 U/mL was verified, and linearity across the analytical measuring range was observed, except at the low end (<20 U/mL). Lastly antibody response showed high inter-individual variation in level and time of peak antibody titre and trends over time.

Background In North America, both mRNA vaccines, Pfizer-BioNTech BNT162b2, and Moderna mRNA-1273, each utilizing a two-dose regimen, have started to be administered to individuals. Methods We evaluated the quantitative serologic antibody response following administration of either a single dose or both doses of an mRNA SARS-CoV-2 vaccine in a cohort of 98 participants (88 healthcare workers [HCW] and 10 solid organ transplant [SOT] recipients). Antibody levels were compared across three immunoassays: Elecsys Anti-SARS-CoV-2 S (Roche Diagnostics), SARS-CoV-2 TrimericS IgG (DiaSorin), and SARS-CoV-2 IgG II Quant (Abbott). Results Among HCW, sensitivity ranged from 100% (Roche), 99% (Abbott) and 98% (DiaSorin). The SARS-CoV-2 IgG II Quant and SARS-CoV-2 TrimericS IgG assays showed good agreement with a Pearson correlation coefficient of R = 0.95. Pearson correlation coefficients of R = 0.82 and 0.83 were obtained for Elecsys Anti-SARS-CoV-2 S vs SARS-CoV-2 TrimericS IgG followed by SARS-CoV-2 IgG II Quant vs Elecsys Anti-SARS-CoV-2 S, respectively. Significant differences in antibody levels between HCW and SOT recipients were observed. A decrease in antibody levels from time of vaccine administration to blood draw was evident. Among those with a second dose, an increase in antibody levels with increased time between administration of the first and second dose was observed. Conclusions The absolute values generated from each of the assay platforms are not interchangeable. Antibody levels differed with increased time between vaccine administration and with increased time between administration of the first and second dose. Further, significant differences in antibody levels between HCW and SOT recipients were observed.

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Serological assays detect the presence of specific antibodies in blood. There are urgent and important applications for serological point-of-care (POC) assays. However, available detection methods are either insufficiently sensitive or too complex for POC settings. Here, we demonstrate that lateral flow immunoassay (LFIA), which is arguably the simplest universal molecular detection approach, can serve as a methodological platform for highly sensitive serological POC assays if combined with a simple, fast, and inexpensive electrophoretic step. In this work, we compared such electrophoretically driven LFIA (eLFIA) with conventional LFIA for the detection of immunoglobulins G against hepatitis B and C in serum. The limit of detection of eLFIA was proven to be 1000 times lower than that of conventional LFIA and sufficiently low to support clinical serological tests. eLFIA takes less than 10 min, requires only a minor accessory powered by a small 9 V battery, and can be performed by an untrained person in the POC environment using a 3 μL specimen of finger-prick capillary blood.