Performance Comparison of Five SARS-CoV-2 Antibody Assays for Seroprevalence Studies

Longitudinal Comparison of Three T-Cell Assays and Three Antibody Assays Against SARS-CoV-2 Following Homologous mRNA-1273/mRNA-1273/mRNA-1273 and Heterologous ChAdOx1/ChAdOx1/BNT162b2 Vaccination: A Prospective Cohort in Naïve Healthcare Workers

Background: Cellular and humoral immunity are key to the immune response against SARS-CoV-2, but the comparability and correlation across different assays remain underexplored. This study compares three T-cell and three antibody assays in two vaccine groups. Methods: This prospective longitudinal cohort study involved 46 naïve healthcare workers: a total of 11 in the homologous mRNA-1273 group (three doses) and 35 in the heterologous ChAd group (two ChAd doses followed by a BNT booster). Blood samples were collected at five time points. Cellular immunity was assessed using ELISPOT and two commercial interferon-gamma release assays: (IGRA)-QuantiFERON SARS-CoV-2 (QF) and Covi-FERON ELISA (CoVF). Humoral immunity was evaluated using total and IgG antibody assays and a surrogate virus neutralization test. Results: The mRNA-1273 group exhibited stronger and more consistent responses than the ChAd group. The correlations between ELISPOT and IGRA varied from weak to moderate (ρ = 0.300-0.410), while QF-IGRA and CoVF-IGRA showed stronger correlations (ρ = 0.700-0.737). The ELISPOT assay showed substantial agreement with QF [Ag2]-IGRA (k = 0.697-0.774) and CoVF [O-sp]-IGRA (k = 0.641-0.718), and an 80.4% agreement rate (k = 0.608) was found between the QF [Ag2]- and CoVF [O-sp]-IGRA tests. Three antibody assays demonstrated very strong correlations with each other and substantial to near-perfect agreement with ELISPOT (k = 0.866-0.949), QF [Ag2]-IGRA (k = 0.807-0.831), and CoVF [O-sp]-IGRA (k = 0.753-0.777). Conclusions: SARS-CoV-2-specific cellular and antibody responses vary by platform and vaccine type, highlighting the importance of measuring both T-cell and B-cell responses using multiple assays to comprehensively assess immune status.

Performance Evaluation of a BZ COVID-19 NALF Assay for Rapid Diagnosis of SARS-CoV-2

Coronavirus disease (COVID-19) caused by SARS-CoV-2 infection has been a global pandemic for more than two years, and it is important to quickly and accurately diagnose and isolate patients with SARS-CoV-2 infection. The BZ COVID-19 NALF Assay could sensitively detect SARS-CoV-2 from a nasopharyngeal swab because it adopts both a loop-mediated isothermal amplification and lateral flow immunochromatography technology. In this study, a total of 389 nasopharyngeal swab samples, of which 182 were SARS-CoV-2 PCR positive and 207 were negative samples, were recruited. Compared to the Allplex™ SARS-CoV-2 Assay, the BZ COVID-19 NALF Assay showed 95.05% sensitivity and 99.03% specificity for detecting SARS-CoV-2. The concordance rate between the BZ COVID-19 NALF Assay and Allplex™ SARS-CoV-2 Assay was 97.69%. The turnaround time of the BZ COVID-19 NALF Assay is only about 40~55 min. The BZ COVID-19 NALF Assay is an accurate, easy, and quick molecular diagnostic test compared to the conventional PCR test for detection of SARS-CoV-2. In addition, the BZ COVID-19 NALF Assay is thought to be very useful in small size medical facilities or developing countries where it is difficult to operate a clinical laboratory.

Comparison of one single-antigen assay and three multi-antigen SARS-CoV-2 IgG assays in Nigeria

Objectives

Determining an accurate estimate of SARS-CoV-2 seroprevalence has been challenging in African countries where malaria and other pathogens are endemic. We compared the performance of one single-antigen assay and three multi-antigen SARS-CoV-2 IgG assays in a Nigerian population endemic for malaria.

Methods

De-identified plasma specimens from SARS-CoV-2 RT-PCR positive, dried blood spot (DBS) SARS-CoV-2 RT-PCR positive, and pre-pandemic negatives were used to evaluate the performance of the four SARS-CoV-2 assays (Tetracore, SARS2MBA, RightSign, xMAP).

Results

Results showed higher sensitivity with the multi-antigen (81% (Tetracore), 96% (SARS2MBA), 85% (xMAP)) versus the single-antigen (RightSign (64%)) SARS-CoV-2 assay. The overall specificities were 98% (Tetracore), 100% (SARS2MBA and RightSign), and 99% (xMAP). When stratified based on <15 days to ≥15 days post-RT-PCR confirmation, the sensitivities increased from 75% to 88.2% for Tetracore; from 93% to 100% for the SARS2MBA; from 58% to 73% for RightSign; and from 83% to 88% for xMAP. With DBS, there was no positive increase after 15-28 days for the three assays (Tetracore, SARS2MBA, and xMAP).

Conclusion

Multi-antigen assays performed well in Nigeria, even with samples with known malaria reactivity, and might provide more accurate measures of COVID-19 seroprevalence and vaccine efficacy.

Update of Guidelines for Laboratory Diagnosis of COVID-19 in Korea

Korean Society for Laboratory Medicine and the Korea Disease Prevention and Control Agency have announced guidelines for diagnosing coronavirus disease (COVID-19) in clinical laboratories in Korea. With the ongoing pandemic, we propose an update of the previous guidelines based on new scientific data. This update includes recommendations for tests that were not included in the previous guidelines, including the rapid molecular test, antigen test, antibody test, and self-collected specimens, and a revision of the previous recommendations. This update will aid clinical laboratories in performing laboratory tests for diagnosing COVID-19.

Humoral and Cellular Responses to BNT162b2 as a Booster Following Two Doses of ChAdOx1 nCov-19 Determined Using Three SARS-CoV-2 Antibody Assays and an Interferon-Gamma Release Assay: A Prospective Longitudinal Study in Healthcare Workers

Data on humoral and cellular responses to BNT162b2 as a booster dose, following two doses of ChAdOx1 nCov-19 vaccine, have seldom been reported. The aim of this study was to assess the positivity rates of three representative antibody assays targeting total, IgG, and neutralizing antibodies, and an interferon-γ release assay (IGRA), and to determine the longitudinal changes in quantitative antibody titers after each vaccination. A total of 1027 samples were collected from healthcare workers. The number of participants after the booster dose was 153, and they all completed a questionnaire on adverse reactions. All antibody assays showed 100.0% positivity at 1 month after booster vaccination. The median antibody titers of the assays were significantly increased compared with those after the second dose (22.1-fold increase for Roche total antibody, 14.0-fold increase for Abbott IgG, and 1.1-fold increase (97.5% inhibition) for GenScript neutralizing antibody). Cellular responses determined using the IGRA were positive in 92.8% of the participants. Most participants (72.5%) reported mild adverse reactions. Correlations between the three antibody assays and IGRA were weak or negligible, indicating a difference between humoral and cellular responses. Overall, our study provides information about booster vaccine strategies and laboratory settings, which could subsequently contribute to the control of the spread of coronavirus disease 2019.

Performance of Severe Acute Respiratory Syndrome Coronavirus 2 Serological Diagnostic Tests and Antibody Kinetics in Coronavirus Disease 2019 Patients

Serological testing is recommended to support the detection of undiagnosed coronavirus disease 2019 (COVID-19) cases. However, the performance of serological assays has not been sufficiently evaluated. Hence, the performance of six severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) binding antibody assays [three chemiluminescence (CLIAs) and three lateral flow immunoassays (LFIAs)] and a surrogate virus neutralization test (sVNT) was analyzed in a total of 988 serum samples comprising 389 COVID-19-positives and 599 COVID-19-negatives. The overall diagnostic sensitivities of CLIAs and LFIAs ranged from 54.2 to 56.6% and from 56.3 to 64.3%, respectively. The overall diagnostic specificities of CLIAs and LFIAs ranged from 98.2 to 99.8% and from 97.3 to 99.0%, respectively. In the symptomatic group (n = 321), the positivity rate increased by over 80% in all assays > 14 days after symptom onset. In the asymptomatic group (n = 68), the positivity rate increased by over 80% in all assays > 21 days after initial RT-PCR detection. In LFIAs, negatively interpreted trace bands accounted for the changes in test performance. Most false-positive results were weak or trace reactions and showed negative results in additional sVNT. For six binding antibody assays, the overall agreement percentages ranged from 91.0 to 97.8%. The median inhibition activity of sVNT was significantly higher in the symptomatic group than in the asymptomatic group (50.0% vs. 29.2%; p < 0.0001). The median times to seropositivity in the symptomatic group were 9.7 days for CLIA-IgG, 9.2 and 9.8 days for two CLIAs-Total (IgM + IgG), 7.7 days for LFIA-IgM, 9.2 days for LFIA-IgG, and 8.8 days for sVNT-IgG, respectively. There was a strong positive correlation between the quantitative results of the four binding antibody assays and sVNT with Spearman ρ-values ranging from 0.746 to 0.854. In particular, when using LFIAs, we recommend using more objective interpretable assays or establishing a band interpretation system for each laboratory, accompanied by observer training. We also anticipate that sVNT will play an essential role in SARS-CoV-2 antibody testing and become the practical routine neutralizing antibody assay.

Prevalence of SARS-CoV-2 Antibody in 2,935 Healthcare Workers at 6 Major Hospitals, Daegu, Korea

BACKGROUND

In Korea, the first community outbreak of coronavirus disease 2019 (COVID-19) occurred in Daegu on February 18, 2020. This study was performed to investigate the prevalence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) antibodies in healthcare workers (HCWs) at 6 major hospitals in Daegu.

METHODS

Blood specimens of 2,935 HCWs at 6 major hospitals in Daegu from January 2021 to February 2021 were collected. Every specimen was tested for antibody against SARS-CoV-2 using both Elecsys Anti-SARS-CoV-2 electrochemiluminescence immunoassay (Roche Diagnostics, Rotkreuz, Switzerland) and R-FIND COVID-19 IgG/M/A enzyme-linked immunosorbent assay kit (SG medical Inc., Seoul, Korea) as screening tests. If 1 or more of these screening test results was positive, 2 additional antibody tests were performed using Abbott Anti-SARS-CoV-2 IgG assay (Abbott, Abbott Park, IL, USA) and cPass SARS-CoV-2 Neutralization Antibody Detection Kit (GenScript USA Inc., Piscataway, NJ, USA). If 2 or more of the total 4 test results were positive, it was determined as positive for the antibody against SARS-CoV-2.

RESULTS

According to the criteria of SARS-CoV-2 antibody positivity determination, 12 subjects were determined as positive. The overall positive rate of the SARS-CoV-2 antibody was 0.41% (12/2,935). Of the 12 subjects determined as positive, 7 were diagnosed with COVID-19, and the remaining 5 were nondiagnosed cases of COVID-19.

CONCLUSION

In early 2021, the overall seroprevalence of SARS-CoV-2 antibody among HCW located in Daegu was 0.41%, and 0.17% excluding COVID-19 confirmed subjects. These results were not particularly high compared with the general public and were much lower than HCWs in other countries.