Assessment of the longitudinal humoral response in non-hospitalized SARS-CoV-2-positive individuals at decentralized sites: Outcomes and concordance

Abstract

IntroductionEarly in the COVID-19 pandemic, reagent availability was not uniform, and infrastructure had to be urgently adapted to undertake COVID-19 surveillance.MethodsBefore the validation of centralized testing, two enzyme-linked immunosorbent assays (ELISA) were established independently at two decentralized sites using different reagents and instrumentation. We compared the results of these assays to assess the longitudinal humoral response of SARS-CoV-2-positive (i.e., PCR-confirmed), non-hospitalized individuals with mild to moderate symptoms, who had contracted SARSCoV-2 prior to the appearance of variants of concern in Québec, Canada.ResultsThe two assays exhibited a high degree of concordance to identify seropositive individuals, thus validating the robustness of the methods. The results also confirmed that serum immunoglobulins persist ≥ 6 months post-infection among non-hospitalized adults and that the antibodies elicited by infection cross-reacted with the antigens from P.1 (Gamma) and B.1.617.2 (Delta) variants of concern.DiscussionTogether, these results demonstrate that immune surveillance assays can be rapidly and reliably established when centralized testing is not available or not yet validated, allowing for robust immune surveillance.

Large-scale validation of a plasmonic sensor for SARS-CoV-2 pseudo-neutralization with a cohort of food and retail workers

“…S4 †). These results are in agreement with the ELISA 55 and the microneutralization 48 data for the same cohort. This is interesting because grocery stores remained open throughout the entire study period, whereas restaurants/bars and hardware stores were required to either temporarily close or exclusively offer drive-through/delivery services during the phases of peak contagion in that district.…”

“…S2 †), where nonlinearities were observed for the in-house colorimetric ELISA (r = 0.37) and chemiluminescence ELISA (r = 0.35). While both ELISA platforms were found to correlate well with each other, 55 lower correlation with the SPR assay is expected, because ELISA measures antibody titers irrespective of their ability to neutralize binding of the spike protein to the ACE-2 receptor. The results indicate that antibody level is a contributing factor in the response of the SPR assay, but not necessarily a major driver.…”

“…The in-house colorimetric ELISA to detect anti-spike (ancestral, Delta B.1.617.2 and Omicron BA.1) antibodies in clinical samples was performed as previously reported. 44 The OD 450 was corrected with the absorbance at 595 nm. Antibody titers (in binding antibody unit per milliliter -BAU mL −1 ), vaccine and natural immunity (expressed as signal to cutoff ratio -SCO ratio) were evaluated at the automated high-throughput chemiluminescent ELISA 45,46 platform that has served as the reference for monitoring SARS-CoV-2 antibodies in Canada.…”

“…We compared the SPR method to ELISA because it is the most widely used method of reporting antibody levels. We used two ELISA platforms, a chemiluminescence ELISA widely used in Canada to study the pandemic 45 and an in-house colorimetric ELISA 44 that was recently shown to correlate with the former. 55 Experimental details, including the optimal dilution factors, were the same as those reported in previous studies.…”

“…We used two ELISA platforms, a chemiluminescence ELISA widely used in Canada to study the pandemic 45 and an in-house colorimetric ELISA 44 that was recently shown to correlate with the former. 55 Experimental details, including the optimal dilution factors, were the same as those reported in previous studies. Antibody levels as measured with ELISA varied temporally as the pandemic progressed showing concordance with vaccination and emergence of new variants.…”