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Serologic assays are an essential tool for seroprevalence surveys, for quality control of vaccines, and to determine the response to vaccination. Although a correlate of immunity has not yet been established for COVID-19 vaccines, antibody titers after natural infection and vaccination have been associated with protection from symptomatic SARS-CoV-2 infection.

The true prevalence and population seropositivity of SARS-CoV-2 infection remains unknown, due to the number of asymptomatic infections and limited access to high-performance antibody tests. To control the COVID-19 pandemic it is crucial to understand the true seroprevalence, but not every region has access to extensive centralized PCR and serology testing. Currently available rapid antibody tests lack the accuracy needed for recommendation by health authorities. To fill this gap, we analyzed and validated the clinical performance of a new point-of-care SARS-CoV-2 Rapid Antibody Assay, a chromatographic immunoassay for qualitative detection of IgM/IgG antibodies for use in near-patient settings. Analysis was performed using 42 Anti-SARS-Cov-2 positive (CoV+) and 92 Anti-SARS-Covid-2 negative (CoV-) leftover samples from before December 2019, using the Elecsys® Anti-SARS-CoV-2 as the reference assay. Analytical specificity was tested using leftover samples from individuals with symptoms of common cold collected before December 2019. The SARS-CoV-2 Rapid Antibody Test was 100.0% (95% CI 91.59-100.00) sensitive and 96.74% (95% CI 90.77-99.32) specific with an assay failure rate of 0.00%. No cross-reactivity was observed against the common cold panel. Method comparison was additionally conducted by two external laboratories, using 100 CoV+/275 CoV- samples, also comparing whole blood versus plasma matrix. The comparison demonstrated for plasma 96.00% positive/96.36% negative percent agreement with the Elecsys Anti-SARS-CoV-2 and overall 99.20% percent agreement between whole blood and EDTA plasma. The SARS-CoV-2 Rapid Antibody Test demonstrated similar clinical performance to the manufacturer's data and to a centralized automated immunoassay, with no cross-reactivity to common cold panels.

Objective The study aimed to establish the performance of the SARS-CoV-2 Rapid Antibody Test (IgG and IgM) and the Elecsys® Anti-SARS-CoV-2 S assay in vaccinated individuals. Methods A panel of serum samples from Boca Biolistics was utilized to assess antibodies following vaccination, consisting of samples drawn prior to vaccination, after the first dose, or at least 14 days after the second dose of Moderna mRNA-1273 or Pfizer-BioNTech BNT162b2 COVID-19 vaccines. Agreement between the two methods was measured and stratified by test evaluator and assay lot. Results Agreement between the SARS-CoV-2 Rapid Antibody Test (IgG) and Elecsys Anti-SARS-CoV-2 S assay qualitative measurements at the different assessment points for both mRNA-1273 and BNT162b2 ranged between 97.06% (95% confidence interval [CI] 84.67, 99.93) to 100% (95% CI 82.35, 100). Agreement of the SARS-CoV-2 Rapid Antibody Test (IgG) with the Elecsys Anti-SARS-CoV-2 S assay was not highly influenced by either lot or evaluator. There was a medium-to-strong correlation between the semi-quantitative SARS-CoV-2 Rapid Antibody Test (IgG) result and quantitative Elecsys Anti-SARS-CoV-2 S assay in samples taken after both doses of the vaccines, with higher intensity bands being associated with higher total anti-S antibody titer (mRNA-1273, p=0.0019; BNT162b2, p<0.0001). Conclusion Semi-quantitative SARS-CoV-2 Rapid Antibody Test (IgG) and quantitative Elecsys Anti-SARS-CoV-2 S assay correlated well, suggesting that the SARS-CoV-2 Rapid Antibody Test (IgG) is helpful in understanding the immune response post-vaccination. The current data support the use of the SARS-CoV-2 Rapid Antibody Test (IgG) in the vaccinated population.