Comparison of two commercial surrogate ELISAs to detect a neutralising antibody response to SARS-CoV-2

Novel Competitive ELISA Utilizing Trimeric Spike Protein of SARS-CoV-2, Could Identify More Than RBD-RBM Specific Neutralizing Antibodies in Hybrid Sera

Since the initiation of the COVID-19 pandemic, there has been a need for the development of diagnostic methods to determine the factors implicated in mounting an immune response against the virus. The most promising indicator has been suggested to be neutralizing antibodies (nAbs), which mainly block the interaction between the Spike protein (S) of SARS-CoV-2 and the host entry receptor ACE2. In this study, we aimed to develop and optimize conditions of a competitive ELISA to measure serum neutralizing titer, using a recombinant trimeric Spike protein modified to have six additional proline residues (S(6P)-HexaPro) and h-ACE2. The results of our surrogate Virus Neutralizing Assay (sVNA) were compared against the commercial sVNT (cPass, Nanjing GenScript Biotech Co., Nanjing City, China), using serially diluted sera from vaccinees, and a high correlation of ID50-90 titer values was observed between the two assays. Interestingly, when we tested and compared the neutralizing activity of sera from eleven fully vaccinated individuals who subsequently contracted COVID-19 (hybrid sera), we recorded a moderate correlation between the two assays, while higher sera neutralizing titers were measured with sVNA. Our data indicated that the sVNA, as a more biologically relevant model assay that paired the trimeric S(6P) with ACE2, instead of the isolated RBD-ACE2 pairing cPass test, could identify nAbs other than the RBD-RBM specific ones.

Comparison of Five Serological Methods for the Detection of West Nile Virus Antibodies

The West Nile Virus (WNV), a member of the family Flaviviridae, is an emerging mosquito-borne flavivirus causing potentially severe infections in humans and animals involving the central nervous system (CNS). Due to its emerging tendency, WNV now occurs in many areas where other flaviviruses are co-occurring. Cross-reactive antibodies with flavivirus infections or vaccination (e.g., tick-borne encephalitis virus (TBEV), Usutu virus (USUV), yellow fever virus (YFV), dengue virus (DENV), Japanese encephalitis virus (JEV)) therefore remain a major challenge in diagnosing flavivirus infections. Virus neutralization tests are considered as reference tests for the detection of specific flavivirus antibodies, but are elaborate, time-consuming and need biosafety level 3 facilities. A simple and straightforward assay for the differentiation and detection of specific WNV IgG antibodies for the routine laboratory is urgently needed. In this study, we compared two commercially available enzyme-linked immunosorbent assays (anti-IgG WNV ELISA and anti-NS1-IgG WNV), a commercially available indirect immunofluorescence assay, and a newly developed in-house ELISA for the detection of WNV-NS1-IgG antibodies. All four tests were compared to an in-house NT to determine both the sensitivity and specificity of the four test systems. None of the assays could match the specificity of the NT, although the two NS1-IgG based ELISAs were very close to the specificity of the NT at 97.3% and 94.6%. The in-house WNV-NS1-IgG ELISA had the best performance regarding sensitivity and specificity. The specificities of the ELISA assays and the indirect immunofluorescence assays could not meet the necessary specificity and/or sensitivity.

Overlaid Lateral Flow Immunoassay for the Simultaneous Detection of Two Variant-Specific SARS-CoV-2 Neutralizing Antibodies

COVID-19 vaccines have been provided to the general public to build immunity since the 2019 coronavirus pandemic. Once vaccinated, SARS-CoV-2 neutralizing antibodies (NAbs-COVID-19) are needed for excellent protection against COVID-19. However, monitoring NAbs-COVID-19 is complicated and requires hospital visits. Moreover, the resulting NAbs-COVID-19 are effective against different strains of COVID-19 depending on the type of vaccine received. Here, an overlaid lateral flow immunoassay (O-LFIA) was developed for the simultaneous detection of two NAbs-COVID-19 against different virus strains, Delta and Omicron. The O-LFIA was visualized with two T-lines with a single device using competition between the free antigen and the antigen-binding antibody. Angiotensin-converting enzyme 2 (ACE2) immobilized on the T-line binds to the antigen remaining after antibody binding. Under the optimum conditions, the proposed device exhibited 50% inhibition concentrations (IC50 values) of 45.1 and 53.6 ng/mL for the Delta and Omicron variants, respectively. Additionally, the proposed platform was applied to real-world samples of animal and human serum, and the developed immunoassay provided results that were in good agreement with those obtained with the standard method. In conclusion, this developed O-LFIA can be used as an alternative method to detect NAbs-COVID-19 and can be enabled for future advancements toward commercialization.

Immunological Response to Subcutaneous and Intranasal Administration of SARS-CoV-2 Spike Protein in Mice

In novel coronavirus infection (COVID-19), the outbreak of acute lung injury due to trans-airway infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the starting point of severe disease. The COVID-19 pandemic highlights the need for a vaccine that prevents not only the disease but also its infection. Currently, the SARS-CoV-2 vaccine is administered via intramuscular injection and is generally not immunogenic to the mucosa. As a result, current vaccinations fail to reduce viral shedding and transmission and ultimately do not prevent infection. We established a mouse vaccine model in which a single dose of S1 protein and aluminum oxide gel (alum) subcutaneous vaccine was followed by a booster dose of S1 protein and CpG oligodeoxynucleotide intranasal vaccine. The group that received two doses of the intranasal vaccine booster showed a significant increase in IgG and IgA antibody titers against S1 and RBD in serum and BAL, and a significant difference in neutralizing antibody titers, particularly in BAL. One intranasal vaccine booster did not induce sufficient immunity, and the vaccine strategy with two booster intranasal doses produced systemic neutralizing antibodies and mucus-neutralizing antibodies against SARS-CoV-2. It will be an important tool against the emergence of new viruses and the next pandemic.

Performance Analysis of Serodiagnostic Tests to Characterize the Incline and Decline of the Individual Humoral Immune Response in COVID-19 Patients: Impact on Diagnostic Management

Serodiagnostic tests for antibody detection to estimate the immunoprotective status regarding SARS-CoV-2 support diagnostic management. This study aimed to investigate the performance of serological assays for COVID-19 and elaborate on test-specific characteristics. Sequential samples (n = 636) of four panels (acute COVID-19, convalescent COVID-19 (partly vaccinated post-infection), pre-pandemic, and cross-reactive) were tested for IgG by indirect immunofluorescence test (IIFT) and EUROIMMUN EUROLINE Anti-SARS-CoV-2 Profile (IgG). Neutralizing antibodies were determined by a virus neutralization test (VNT) and two surrogate neutralization tests (sVNT, GenScript cPass, and EUROIMMUN SARS-CoV-2 NeutraLISA). Analysis of the acute and convalescent panels revealed high positive (78.3% and 91.6%) and negative (91.6%) agreement between IIFT and Profile IgG. The sVNTs revealed differences in their positive (cPass: 89.4% and 97.0%, NeutraLISA: 71.5% and 72.1%) and negative agreement with VNT (cPass: 92.3% and 50.0%, NeutraLISA: 95.1% and 92.5%) at a diagnostic specificity of 100% for all tests. The cPass showed higher inhibition rates than NeutraLISA at VNT titers below 1:640. Cross-reactivities were only found by cPass (57.1%). Serodiagnostic tests, which showed substantial agreement and fast runtime, could provide alternatives for cell-based assays. The findings of this study suggest that careful interpretation of serodiagnostic results obtained at different times after SARS-CoV-2 antigen exposure is crucial to support decision-making in diagnostic management.

Validation of a SARS-CoV-2 Surrogate Neutralization Test Detecting Neutralizing Antibodies against the Major Variants of Concern

SARS-CoV-2 infection and/or vaccination elicit a broad range of neutralizing antibody responses against the different variants of concern (VOC). We established a new variant-adapted surrogate virus neutralization test (sVNT) and assessed the neutralization activity against the ancestral B.1 (WT) and VOC Delta, Omicron BA.1, BA.2, and BA.5. Analytical performances were compared against the respective VOC to the reference virus neutralization test (VNT) and two CE-IVD labeled kits using three different cohorts collected during the COVID-19 waves. Correlation analyses showed moderate to strong correlation for Omicron sub-variants (Spearman's r = 0.7081 for BA.1, r = 0.7205 for BA.2, and r = 0.6042 for BA.5), and for WT (r = 0.8458) and Delta-sVNT (r = 0.8158), respectively. Comparison of the WT-sVNT performance with two CE-IVD kits, the "Icosagen SARS-CoV-2 Neutralizing Antibody ELISA kit" and the "Genscript cPass, kit" revealed an overall good correlation ranging from 0.8673 to -0.8773 and a midway profile between both commercial kits with 87.76% sensitivity and 90.48% clinical specificity. The BA.2-sVNT performance was similar to the BA.2 Genscript test. Finally, a correlation analysis revealed a strong association (r = 0.8583) between BA.5-sVNT and VNT sVNT using a double-vaccinated cohort (n = 100) and an Omicron-breakthrough infection cohort (n = 91). In conclusion, the sVNT allows for the efficient prediction of immune protection against the various VOCs.

SARS-CoV-2 Serological Investigation of White-Tailed Deer in Northeastern Ohio

Coronaviruses are known to cross species barriers, and spill over among animals, from animals to humans, and vice versa. SARS-CoV-2 emerged in humans in late 2019. It is now known to infect numerous animal species, including companion animals and captive wildlife species. Experimental infections in other animals have established that many species are susceptible to infection, with new ones still being identified. We have developed an enzyme-linked immunosorbent assay (ELISA) for detecting antibodies to SARS-CoV-2 nucleocapsid (N) and spike (S) proteins, that is both sensitive and specific. It can detect S antibodies in sera at dilutions greater than 1:10,000, and does not cross-react with antibodies to the other coronaviruses tested. We used the S antibody ELISA to test serum samples collected from 472 deer from ten sites in northeastern Ohio between November 2020 and March 2021, when the SARS-CoV-2 pandemic was first peaking in humans in Ohio, USA. Antibodies to SARS-CoV-2 were found in serum samples from every site, with an overall positivity rate of 17.2%; we further compared the viral neutralizing antibody titers to our ELISA results. These findings demonstrate the need to establish surveillance programs to monitor deer and other susceptible wildlife species globally.

Detection of SARS-CoV-2 Antibodies: Comparison of Enzyme Immunoassay, Surrogate Neutralization and Virus Neutralization Test

BACKGROUND

Since sensitivity and specificity vary widely between tests, SARS-CoV-2 serology results should be interpreted with caution.

METHODS

The study included serum samples from patients who had recovered from COVID-19 (n = 71), individuals vaccinated against SARS-CoV-2 (n = 84), and asymptomatic individuals (n = 33). All samples were tested for the presence of binding antibodies (enzyme immunoassay; EIA), neutralizing (NT) antibodies (virus neutralization test; VNT), and surrogate NT (sNT) antibodies (surrogate virus neutralization test; sVNT) of SARS-CoV-2.

RESULTS

SARS-CoV-2-binding antibodies were detected in 71 (100%) COVID-19 patients, 77 (91.6%) vaccinated individuals, and 4 (12.1%) control subjects. Among EIA-positive samples, VNT was positive (titer ≥ 8) in 100% of COVID-19 patients and 63 (75.0%) of the vaccinated individuals, while sVNT was positive (>30% inhibition) in 62 (87.3%) patients and 59 (70.2%) vaccinated individuals. The analysis of antibody levels showed a significant moderate positive correlation between EIA and VNT, a moderate positive correlation between EIA and sVNT, and a strong positive correlation between VNT and sVNT. The proportion of positive sVNT detection rate was associated with VNT titer. The lowest positivity (72.4%/70.8%) was detected in samples with low NT titers (8/16) and increased progressively from 88.2% in samples with titer 32 to 100% in samples with titer 256.

CONCLUSIONS

sVNT appeared to be a reliable method for the assessment COVID-19 serology in patients with high antibody levels, while false-negative results were frequently observed in patients with low NT titers.

Comprehensive Comparison of Seven SARS-CoV-2-Specific Surrogate Virus Neutralization and Anti-Spike IgG Antibody Assays Using a Live-Virus Neutralization Assay as a Reference

Neutralizing antibodies (nAbs) are considered a valuable marker for measuring humoral immunity against SARS-CoV-2. However, live-virus neutralization tests (NTs) require high-biosafety-level laboratories and are time-consuming. Therefore, surrogate virus neutralization tests (sVNTs) have been widely applied, but unlike most anti-spike (S) antibody assays, NTs and sVNTs are not harmonized, requiring further evaluation and comparative analyses. This study compared seven commercial sVNTs and anti-S-antibody assays with a live-virus NT as a reference, using a panel of 720 single and longitudinal serum samples from 666 convalescent patients after SARS-CoV-2 infection. The sensitivity of these assays for detecting antibodies ranged from 48 to 94% after PCR-confirmed infection and from 56% to 100% relative to positivity in the in-house live-virus NT. Furthermore, we performed receiver operating characteristic (ROC) curve analyses to determine which immunoassays were most suitable for assessing nAb titers exceeding a specific cutoff (NT titer, ≥80) and found that the NeutraLISA and the cPass assays reached the highest area under the curve (AUC), exceeding 0.91. In addition, when the assays were compared for their correlation with nAb kinetics over time in a set of longitudinal samples, the extent of the measured decrease of nAbs after infection varied widely among the evaluated immunoassays. Finally, in vaccinated convalescent patients, high titers of nAbs exceeded the upper limit of the evaluated assays' quantification ranges. Based on data from this study, we conclude that commercial immunoassays are acceptable substitutes for live-virus NTs, particularly when additional adapted cutoffs are employed to detect nAbs beyond a specific threshold titer. IMPORTANCE While the measurement of neutralizing antibodies is considered a valuable tool in assessing protection against SARS-CoV-2, neutralization tests employ live-virus isolates and cell culture, requiring advanced laboratory biosafety levels. Including a large sample panel (over 700 samples), this study provides adapted cutoff values calculated for seven commercial immunoassays (including four surrogate neutralization assays and a protein-based microarray) that robustly correlate with specific titers of neutralizing antibodies.

Evaluation of commercially available fully automated and ELISA-based assays for detecting anti-SARS-CoV-2 neutralizing antibodies

Rapid and accurate measurement of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV2)-specific neutralizing antibodies (nAbs) is paramount for monitoring immunity in infected and vaccinated subjects. The current gold standard relies on pseudovirus neutralization tests which require sophisticated skills and facilities. Alternatively, recent competitive immunoassays measuring anti-SARS-CoV-2 nAbs are proposed as a quick and commercially available surrogate virus neutralization test (sVNT). Here, we report the performance evaluation of three sVNTs, including two ELISA-based assays and an automated bead-based immunoassay for detecting nAbs against SARS-CoV-2. The performance of three sVNTs, including GenScript cPass, Dynamiker, and Mindray NTAb was assessed in samples collected from SARS-CoV-2 infected patients (n = 160), COVID-19 vaccinated individuals (n = 163), and pre-pandemic controls (n = 70). Samples were collected from infected patients and vaccinated individuals 2-24 weeks after symptoms onset or second dose administration. Correlation analysis with pseudovirus neutralization test (pVNT) and immunoassays detecting anti-SARS-CoV-2 binding antibodies was performed. Receiver operating characteristic (ROC) curve analysis was generated to assess the optimal threshold for detecting nAbs by each assay. All three sVNTs showed an excellent performance in terms of specificity (100%) and sensitivity (100%, 97.0%, and 97.1% for GenScript, Dynamiker, and Mindray, respectively) in samples collected from vaccinated subjects. GenScript demonstrated the strongest correlation with pVNT (r = 0.743, R² = 0.552), followed by Mindray (r = 0.718, R² = 0.515) and Dynamiker (r = 0.608, R² = 0.369). Correlation with anti-SARS-CoV-2 binding antibodies was variable, but the strongest correlations were observed between anti-RBD IgG antibodies and Mindray (r = 0.952, R² = 0.907). ROC curve analyses demonstrated excellent performance for all three sVNT assays in both groups, with an AUC ranging between 0.99 and 1.0 (p < 0.0001). Also, it was shown that the manufacturer's recommended cutoff values could be modified based on the tested cohort without significantly affecting the sVNT performance. The sVNT provides a rapid, low-cost, and scalable alternative to conventional neutralization assays for measuring and expanding nAbs testing across various research and clinical settings. Also, it could aid in evaluating actual protective immunity at the population level and assessing vaccine effectiveness to lay a foundation for boosters' requirements.

Antibody dynamics post-Comirnaty and CoronaVac vaccination in Malaysia

Several vaccines have been fast-tracked through clinical trials to mitigate the progression of the SARS‑CoV‑2 pandemic. We analyzed sequential blood samples from 314 recipients of Comirnaty and CoronaVac in East Malaysia for the spike-binding IgG (IgG-S), nucleocapsid-binding IgG (IgG-N), spike-binding IgM (IgM-S) and serum vitamin D (VitD). A subset of samples was analyzed for the neutralizing antibodies (Ig-RBD). Results showed that IgG-S due to Comirnaty was significantly higher than CoronaVac. IgM-S was detected in 80.0% Comirnaty and 69.5% CoronaVac recipients, while IgG-N was detected in 58.1% CoronaVac but not in Comirnaty recipients. All IgG-S-positive vaccines possessed detectable Ig-RBD after the second dose but with a weak to moderate correlation. The serum VitD levels did not influence the antibody magnitude in both vaccines. In essence, SARS-CoV-2 vaccination is an IgG-S-dominant event, Comirnaty was more effective than CoronaVac in mounting IgG-S and Ig-RBD responses, independent of the patient’s VitD level.

Proof-of-concept for speedy development of rapid and simple at-home method for potential diagnosis of early COVID-19 mutant infections using nanogold and aptamer

The positive single-stranded nature of COVID-19 mRNA led to the low proof-reading efficacy for its genome authentication. Thus mutant covid-19 strains have been rapidly evolving. Besides Alpha, Beta, Gamma, Delta, and Omicron variants, currently, subvariants of omicron are circulating, including BA.4, BA.5, and BA.2.12.1. Therefore, the speedy development of a rapid, simple, and easier diagnosis method to deal with new mutant covid viral infection is critically important. Many diagnosis methods have been developed for COVID-19 detection such as RT-PCR and antibodies detection. However, the former is time-consuming, laborious, and expensive, and the latter relies on the production of antibodies making it not suitable for the early diagnosis of viral infection. Many lateral-flow methods are available but might not be suitable for detecting the mutants, Here we proved the concept for the speedy development of a simple, rapid, and cost-effective early at-home diagnosis method for mutant Covid-19 infection by combining a new aptamer. The idea is to use the current lateral flow Covid-19 diagnosis system available in the market or to use one existing antibody for the Lateral Flow Nitrocellulose filter. To prove the concept, the DNA aptamer specific to spike proteins (S-proteins) was conjugated to gold nanoparticles and served as a detection probe. An antibody that is specific to spike proteins overexpressed on COVID viral particles was used as a second probe immobilized to the nitrocellulose membrane. The aptamer conjugated nanoparticles were incubated with spike proteins for half an hour and tested for their ability to bind to antibodies anchored on the nitrocellulose membrane. The gold nanoparticles were visualized on the nitrocellulose membrane due to interaction between the antigen (S-protein) with both the aptamer and the antibody. Thus, the detection of viral antigen can be obtained within 2 h, with a cost of less than $5 for the diagnosis reagent. In the future, as long as the mutant of the newly emerged viral surface protein is reported, a peptide or protein corresponding to the mutation can be produced by peptide synthesis or gene cloning within several days. An RNA or DNA aptamer can be generated quickly via SELEX. A gold-labeled aptamer specific to spike proteins (S-proteins) will serve as a detection probe. Any available lateral-flow diagnosis kits with an immobilized antibody that has been available on the market, or simply an antibody that binds COVID-19 virus might be used as a second probe immobilized on the nitrocellulose. The diagnosis method can be carried out by patients at home if a clinical trial verifies the feasibility and specificity of this method.

Review of COVID-19 testing and diagnostic methods

More than six billion tests for COVID-19 has been already performed in the world. The testing for SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus-2) virus and corresponding human antibodies is essential not only for diagnostics and treatment of the infection by medical institutions, but also as a pre-requisite for major semi-normal economic and social activities such as international flights, off line work and study in offices, access to malls, sport and social events. Accuracy, sensitivity, specificity, time to results and cost per test are essential parameters of those tests and even minimal improvement in any of them may have noticeable impact on life in the many countries of the world. We described, analyzed and compared methods of COVID-19 detection, while representing their parameters in 22 tables. Also, we compared test performance of some FDA approved test kits with clinical performance of some non-FDA approved methods just described in scientific literature. RT-PCR still remains a golden standard in detection of the virus, but a pressing need for alternative less expensive, more rapid, point of care methods is evident. Those methods that may eventually get developed to satisfy this need are explained, discussed, quantitatively compared. The review has a bioanalytical chemistry prospective, but it may be interesting for a broader circle of readers who are interested in understanding and improvement of COVID-19 testing, helping eventually to leave COVID-19 pandemic in the past.

Heterologous immunization with BNT162b2 followed by mRNA-1273 in dialysis patients: seroconversion and presence of neutralizing antibodies

INTRODUCTION

The vital renal replacement therapy makes it impossible for dialysis patients to distance themselves socially. This results in a high risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and developing coronavuris disease 2019, with excess mortality due to disease burden and immunosuppression. We determined the efficacy of a 100-µg booster of mRNA-1273 (Moderna, Cambridge, MA, USA) 6 months after two doses of BNT162b2 (BioNTech/Pfizer, Mainz, Germany/New York, USA) in 194 SARS-CoV-2-naïve dialysis patients.

METHODS

Anti-SARS-CoV-2 spike antibodies were measured with the Elecsys Anti-SARS-CoV-2 S assay (Roche Diagnostics, Mannheim, Germany) 4 and 10-12 weeks after two doses of BNT162b2 as well as 4 weeks after the mRNA-1273 booster. The presence of neutralizing antibodies was measured by the SARS-CoV-2 Surrogate Virus Neutralization Test (GenScript Biotech, Piscataway, NJ, USA). Two different cut-offs for positivity were used, one according to the manufacturer's specifications and one correlating with positivity in a plaque reduction neutralization test (PRNT). Receiver operating characteristics analyses were performed to match the anti-SARS-CoV-2 spike antibody cut-offs with the cut-offs in the surrogate neutralization assay accordingly.

RESULTS

Any level of immunoreactivity determined by the anti-SARS-CoV-2 spike antibody assay was found in 87.3% (n = 144/165) and 90.6% (n = 164/181) of patients 4 and 10-12 weeks, respectively, after two doses of BNT162b2. This was reduced to 68.5% or 60.6% 4 weeks and 51.7% or 35.4% 10-12 weeks, respectively, when using the ROC cut-offs for neutralizing antibodies in the surrogate neutralization test (manufacturer's cut-off ≥103 U/mL and cut-off correlating with PRNT ≥196 U/mL). Four weeks after the mRNA-1273 booster, the concentration of anti-SARS-CoV-2 spike antibodies increased to 23 119.9 U/mL and to 97.3% for both cut-offs of neutralizing antibodies.

CONCLUSION

Two doses of BNT162b2 followed by one dose of mRNA-1273 within 6 months in patients receiving maintenance dialysis resulted in significant titres of SARS-CoV-2 spike antibodies. While two doses of mRNA vaccine achieved adequate humoral immunity in a minority, the third vaccination boosts the development of virus-neutralizing quantities of SARS-CoV-2 spike antibodies (against wild-type SARS-CoV-2) in almost all patients.

Inactivated Vaccines Against SARS-CoV-2: Neutralizing Antibody Titers in Vaccine Recipients

Background

Although effective vaccines have been developed against coronavirus disease 2019 (COVID-19), the level of neutralizing antibodies (NAbs) induced after vaccination in the real world is still unknown. The aim of this work was to evaluate the level and persistence of NAbs induced by two inactivated COVID-19 vaccines in China.

Methods

Serum samples were collected from 1,335 people aged 18 years and over who were vaccinated with an inactivated COVID-19 vaccine at Peking University People’s Hospital from January 19 to June 23, 2021, for the detection of anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies.

Results

The positive rate for NAbs against SARS-CoV-2 was 79–91% from the first month to the second month after the second vaccine dose. The gradual decline in positivity rate for NAb response was observed from 78% at 3 months post-vaccination to 0% at 12 months post-vaccination. When there was a 21-day interval between the two doses of vaccine, the NAb positivity rate was 0% 6 months after the second dose. NAb levels were significantly higher when the interval between two doses were 3–8 weeks than when it was 0–3 weeks (χ2 = 14.04, p < 0.001). There was a linear correlation between NAbs and IgG antibodies in 1,335 vaccinated patients. NAb levels decreased in 31 patients (81.6%) and increased in 7 patients (18.4%) over time in the series of 38 patients after the second vaccination. The NAb positivity rate was significantly higher in 18- to 40-year-old subjects than in 41- to 60-year-old subjects (t = −1.959, p < 0.01; t = 0.839, p < 0.01).

Conclusion

The NAb positivity rate was the highest at the first and second month after the second dose of vaccine, and gradually decreased over time. With a 21-day interval between two doses of vaccine, neutralizing antibody levels persisted for only 6 months after the second dose of vaccine. Therefore, a third vaccine dose is recommended. Our results suggest that in cases in which NAbs cannot be detected, IgM/IgG antibodies can be detected instead. The level of NAbs produced after vaccination was affected by age but not by sex. Our results suggest that an interval of 21 to 56 days between shots is suitable for vaccination.

Evaluation of a commercial ELISA as alternative to plaque reduction neutralization test to detect neutralizing antibodies against SARS-CoV-2

High-throughput detection of neutralizing antibodies against SARS-CoV-2 presents a valuable tool for vaccine trials or investigations of population immunity. We evaluate the performance of the first commercial surrogate virus neutralization test (sVNT, GenScript Biotech) against SARS-CoV-2 plaque reduction neutralization test (PRNT) in convalescent and vaccinated individuals. We compare it to five other ELISAs, two of which are designed to detect neutralizing antibodies. In 491 pre-vaccination serum samples, sVNT missed 23.6% of PRNT-positive samples when using the manufacturer-recommended cutoff of 30% binding inhibition. Introducing an equivocal area between 15 and 35% maximized sensitivity and specificity against PRNT to 72.8–93.1% and 73.5–97.6%, respectively. The overall diagnostic performance of the other ELISAs for neutralizing antibodies was below that of sVNT. Vaccinated individuals exhibited higher antibody titers by PRNT (median 119.8, IQR 56.7–160) and binding inhibition by sVNT (median 95.7, IQR 88.1–96.8) than convalescent patients (median 49.1, IQR 20–62; median 52.9, IQR 31.2–76.2). GenScript sVNT is suitable to screen for SARS-CoV-2-neutralizing antibodies; however, to obtain accurate results, confirmatory testing by PRNT in a equivocal area is required. This equivocal area may require adaptation for use in vaccinated individuals, due to higher antibody titers.

A method comparison of three immunoassays for detection of neutralizing antibodies against SARS-CoV-2 receptor-binding domain in individuals with adenovirus type-5-vectored COVID-19 vaccination

Objective

Detecting neutralizing antibodies targeting receptor‐binding domain (RBD) is important for the assessment of humoral protection and vaccine efficacy after vaccination. We compared the performance of three surrogate immunoassays for detection of neutralizing antibodies targeting RBD.

Methods

We analyzed 115 serum samples obtained from individuals with Ad5‐vectored COVID‐19 vaccination using two competitive enzyme‐linked immunosorbent assays (Wantai BioPharm and Synthgene Medical Technology) and one competitive chemiluminescence assay (YHLO Biotech). Performance evaluation and methodology comparison were performed according to the Clinical and Laboratory Standards Institute related guidelines.

Results

The precision met the manufacturers’ statements. The linear range of the WANTAI was 0.0625–0.545 U/ml and the YHLO was 0.260–242.4 U/ml. The WANTAI’s limit of blank (LoB) and limit of detection (LoD) were 0.03 and 0.06 U/ml, respectively. The YHLO’s LoB and LoD were 0.048 and 0.211 U/ml, respectively. The correlations of semi‐quantitative results of Synthgene with quantitative results of YHLO (ρ = 0.566) and WANTAI (ρ = 0.512) were medium. For YHLO and WANTAI, there was a good agreement (0.62) and a strong correlation (ρ = 0.931). Passing–Bablok analysis and Bland‐Altman plot showed a positive bias (112.3%) of the YHLO compared to the WANTAI. The exclusion of samples >50 U/ml did not decrease bias.

Conclusion

These findings contribute to a deeper understanding of surrogate viral neutralization assays and provide useful data for future comparison studies.

Multiplexed Lab-on-a-Chip Bioassays for Testing Antibodies against SARS-CoV-2 and Its Variants in Multiple Individuals

Neutralization assays that can measure neutralizing antibodies in serum are vital for large-scale serodiagnosis and vaccine evaluation. Here, we establish multiplexed lab-on-a-chip bioassays for testing antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its variants. Compared with enzyme-linked immunosorbent assay (ELISA), our method exhibits a low consumption of sample and reagents (10 μL), a low limit of detection (LOD: 0.08 ng/mL), a quick sample-to-answer time (about 70 min), and multiplexed ability (5 targets in each of 7 samples in one assay). We can also increase the throughput as needed. The concentrations of antibodies against RBD, D614G, N501Y, E484K, and L452R/E484Q-mutants after two doses of vaccines are 6.6 ± 3.6, 8.7 ± 4.6, 3.4 ± 2.8, 3.8 ± 2.8, and 2.8 ± 2.3 ng/mL, respectively. This suggests that neutralizing activities against N501Y, E484K, and L452R/E484Q-mutants were less effective than RBD and D614G-mutant. We performed a plaque reduction neutralization test (PRNT) for all volunteers. Compared with PRNT, our assay is fast, accurate, inexpensive, and multiplexed with multiple-sample processing ability, which is good for large-scale serodiagnosis and vaccine evaluation.

Evaluation of Two Rapid Lateral Flow Tests and Two Surrogate ELISAs for the Detection of SARS-CoV-2 Specific Neutralizing Antibodies

As vaccination against SARS-CoV-2 progresses rapidly around the world, reliable detection of SARS-CoV-2 specific neutralizing antibodies (NAb) has become an indispensable component of serological diagnostics. We evaluated the performance of four commercially available tests, i.e. two lateral flow assays (Coris BioConcept COVID-19 Sero NP/RBD and Concile InfectCheck COVID-19 NAb) and two surrogate ELISA (sELISA) tests (EUROIMMUN SARS-CoV-2 NeutraLISA and AdipoGen SARS-CoV-2 Neutralizing Antibodies Detection Kit) in comparison with an in-house SARS-CoV-2 micro neutralization test as reference. A total of 334 sera were tested, including 30 samples collected prior to the emergence of SARS-CoV-2, 128 sera from convalescent patients as well as 176 sera from partially or fully vaccinated individuals. The overall sensitivity of LFAs differed and was 71.6% for the Coris and 98.4% for the Concile. In contrast, overall sensitivity of the NeutraLISA was 86 and 98% for the AdipoGen. All test showed the highest sensitivity when testing samples from fully vaccinated individuals with both sELISA achieving 100% sensitivity. Overall specificity was 89.3% for the Coris and only 58.3% for the Concile. Similarly, significant differences were observed for both sELISA, with an overall specificity of 82.1% for the NeutraLISA and only 54.8% for the AdipoGen. All tests showed a 100% specificity when testing negative control samples while specificities were lowest when testing samples from only partially vaccinated individuals.

Comparison of the Anti-SARS-CoV-2 Surrogate Neutralization Assays by TECOmedical and DiaPROPH-Med with Samples from Vaccinated and Infected Individuals

Anti-SARS-CoV-2-specific serological responses are a topic of ongoing evaluation studies. In the study presented here, the anti-SARS-CoV-2 surrogate neutralization assays by TECOmedical and DiaPROPH -Med were assessed in a head-to-head comparison with serum samples of individuals after vaccination as well as after previous infection with SARS-CoV-2. In case of discordant results, a cell culture-based neutralization assay was applied as a reference standard. The TECOmedical assay showed sensitivity and specificity of 100% and 61.3%, respectively, the DiaPROPH-Med assay 95.0% and 48.4%, respectively. As a side finding of the study, differences in the likelihood of expressing neutralizing antibodies could be shown for different exposition types. So, 60 of 81 (74.07%) of the samples with only one vaccination showed an expression of neutralizing antibodies in contrast to 85.71% (60 of 70 samples) of the samples with two vaccinations and 100% (40 of 40) of the samples from previously infected individuals. In conclusion, the both assays showed results similar to previous assessments. While the measured diagnostic accuracy of both assays requires further technical improvement of this diagnostic approach, as the calculated specificity values of 61.3% and 48.4%, respectively, appear acceptable for diagnostic use only in populations with a high percentage of positive subjects, but not at expectedly low positivity rates.

Immunogenicity and safety of two doses of the CoronaVac SARS-CoV-2 vaccine in SARS-CoV-2 seropositive and seronegative patients with autoimmune rheumatic diseases in Brazil: a subgroup analysis of a phase 4 prospective study

Background

We aimed to examine the immunogenicity pattern induced by the inactivated SARS-CoV-2 vaccine CoronaVac (Sinovac Life Sciences, Beijing, China) in SARS-CoV-2 seropositive patients with autoimmune rheumatic diseases compared with seropositive controls, seronegative patients with autoimmune rheumatic diseases, and seronegative controls.

Methods

CoronavRheum is an ongoing, prospective, controlled, phase 4 study, in which patients aged 18 years or older with autoimmune rheumatic diseases, and healthy controls were recruited from a single site (Rheumatology Division of Hospital das Clínicas, Faculdade de Medicina da Universidade de São Paulo) in São Paulo, Brazil Participants were vaccinated with two doses of CoronaVac (intramuscular injection, 3 μg in 0·5 mL of β-propiolactone inactivated SARS-CoV-2) on day 0 and on day 28. Blood samples were taken pre-vaccination on day 0, day 28, and also on day 69. For this subgroup analysis, participants were defined as being SARS-CoV-2 seropositive or seronegative prevaccination via anti-SARS-CoV-2 spike (S)1 or S2 IgG (cutoff of 15·0 arbitrary units [AU] per mL) or neutralising antibody titres (cutoff of ≥30%) and were matched for age and sex, via convenience sampling, in a 1:3:1:1 ratio (seropositive patients to seronegative patients to seropositive controls to seronegative controls). The primary outcomes were rates of anti-SARS-CoV-2 S1 and S2 IgG seropositivity and SARS-CoV-2 neutralising antibody positivity at day 28 and day 69 and immunogenicity dynamics assessed by geometric mean titres (GMTs) of IgG and median neutralising activity in seropositive patients with autoimmune rheumatic diseases compared with seronegative patients and seropositive and seronegative controls. We assessed safety in all participants randomly selected for this subgroup analysis. This study is registered with ClinicalTrials.gov, NCT04754698, and is ongoing for long-term immunogenicity evaluation.

Findings

Between Feb 4 and Feb 8, 2021, 1418 patients and 542 controls were recruited, of whom 1685 received two vaccinations (1193 patients and 492 controls). After random sampling, our immunogenicity analysis population comprised 942 participants, of whom 157 were SARS-CoV-2 seropositive patients with autoimmune rheumatic diseases, 157 were seropositive controls, 471 were seronegative patients, and 157 were seronegative controls; the median age was 48 years (IQR 38–56) and 594 (63%) were female and 348 (37%) were male. For seropositive patients and controls, an increase in anti-SARS-CoV-2 S1 and S2 IgG titres (seropositive patients GMT 52·3 [95% CI 42·9–63·9] at day 0 vs 128·9 [105·6–157·4] at day 28; seropositive controls 53·3 [45·4–62·5] at day 0 vs 202·0 [174·8–233·4] at day 28) and neutralising antibody activity (seropositive patients 59% [IQR 39–83] at day 0 vs 82% [54–96] at day 28; seropositive controls 58% [41–79] at day 0 vs 92% [79–96] at day 28), was observed from day 0 to day 28, without further increases from day 28 to day 69 (at day 69 seropositive patients' GMT was 137·1 [116·2–161·9] and neutralising antibody activity was 79% [57–94]); and seropositive controls' GMT was 188·6 [167·4–212·6] and neutralising antibody activity was 92% [75–96]). By contrast, for seronegative patients and controls, the second dose was required for maximum response at day 69, which was lower in seronegative patients than in seronegative controls. GMTs in seronegative patients were 2·3 (95% CI 2·2–2·3) at day 0, 5·7 (5·1–6·4) at day 28, and 29·6 (26·4–33·3) at day 69, and in seronegative controls were 2·3 (2·1–2·5) at day 0, 10·6 (8·7–13·1) at day 28, and 71·7 (63·5–81·0) at day 69; neutralising antibody activity in seronegative patients was 15% (IQR 15–15) on day 0, 15% (15–15) at day 28, and 39% (15–65) at day 69, and in seronegative controls was 15% (15–15) at day 0, 24% (15–37) at day 28, and 61% (37–79) at day 69. Neither seronegative patients nor seronegative controls reached the GMT or antibody activity levels of seropositive patients at day 69.

Interpretation

By contrast with seronegative patients with autoimmune rheumatic diseases, seropositive patients have a robust response after a single dose of CoronaVac. Our findings raise the possibility that the reduced immunogenicity observed in seronegative patients might not be the optimum response potential to SARS-CoV-2 vaccination, and therefore emphasise the importance of at least a single booster vaccination in these patients.

Funding

Fundação de Amparo à Pesquisa do Estado de São Paulo, Conselho Nacional de Desenvolvimento Científico e Tecnológico, and B3-Bolsa de Valores do Brasil.

Translation

For the Portuguese translation of the abstract see Supplementary Materials section.

Two novel SARS-CoV-2 surrogate virus neutralization assays are suitable for assessing successful immunization with mRNA-1273

BACKGROUND

Due to large vaccination efforts with novel vaccines there is an increasing need for laboratory tests assessing successful immunizations with SARS-CoV-2 vaccines. Unfortunately classical neutralization assays are laborious, time-consuming and require an adequate biosafety level laboratory. Recently, convenient ELISA-based surrogate neutralization assays (sVNTs) for determination of neutralizing SARS-CoV-2 antibodies have been developed.

STUDY DESIGN

Our study compares the two novel ELISA-based SARS-CoV-2 surrogate neutralization assays "cPass SARS-CoV-2 Surrogate Virus Neutralization Test Kit" (GenScript Biotech, USA) and the "TECO SARS-CoV-2 Neutralization Antibody Assay" (TECOmedical, Switzerland) using 93 sera drawn from health care workers (HCVs) 2-3 weeks following the second vaccination with mRNA-1273 and 40 control sera from the pre-SARS-CoV-2 era before 2019.

RESULTS

We found a sensitivity of 100% and 91,4% and a specificity of 100% and 100% for the GenScript assay and the TECO assay, respectively. Both sVNTs show a high correlation with anti-S IgG. Moreover, both sVNTs correlate well with each other.

CONCLUSIONS

Surrogate neutralization assays based on the RBD as bait feature a high specificity and sensitivity for identifying humoral neutralizing activity in individuals vaccinated with the spike-based vaccine mRNA-1273. Although these assays appear well-suited for confirming successful vaccinations with spike-based vaccines, additional studies should compare both assays regarding other purposes such as screening COVID-recovered patients or individuals vaccinated with inactivated whole virus vaccines.

Long-term decay of anti-RBD IgG titers after BNT162b2 vaccination is not mirrored by loss of neutralizing bioactivity against SARS-CoV-2

BACKGROUND AND AIMS

Long-term kinetics of anti-RBD IgG and neutralizing antibodies were analyzed in a cohort of COVID-19 naïve health care workers (HCW) undergoing SARS-CoV-2 vaccination.

METHODS

An anti-RBD IgG immunoassay and a surrogate virus neutralization test (sVNT) were performed at different time points up to 6 months after vaccination in 57 HCWs. Values of anti-RBD IgG predicting an high neutralizing bioactivity (>60%) were also calculated.

RESULTS

Mean (range) values of anti-RBD IgG were 294.7 (11.6-1554), 2583 (398-8391), 320.4 (42.3-1134) BAU/mL at T1 (21 days after the 1st dose [T0]), T2 (30 days after the 2nd dose) and T3 (+180 days after T0), respectively. Mean (range) percentages of neutralization (NS%) were 24 (0-76), 86 (59-96) and 82 (52-99) at T1, T2 and T3, respectively. Anti-RBD IgG values and NS% were positively correlated at T2 and T3 while anti-RBD IgG value predicting a NS% > 60 markedly differed at T2 and T3 (594 vs. 108 BAU/mL, respectively).

CONCLUSION

While a high neutralizing bioactivity was maintained at least 6 months after vaccination in almost all individuals, the mean values of anti-RBD-IgG showed a marked decline at 6 months. The absolute value of anti-RBD IgG is a poor marker of neutralizing bioactivity.

Evaluation of the QuantiFERON SARS-CoV-2 interferon-ɣ release assay in mRNA-1273 vaccinated health care workers

Current studies focus on cellular and humoral immunity induced by novel SARS-CoV-2 vaccines. Non-responders to vaccinations are not uncommonly encountered in clinical medicine (e.g. in the field of hepatitis B). Whereas vaccine-induced humoral immunity against SARS-CoV-2 is compromised by emerging Variants of Concern (VOCs), cellular immunity against SARS-CoV-2 is emerging as resilient against VOCs. Thus commercially available test kits for diagnostic laboratories designed to evaluate cellular immune responses to SARS-CoV-2 are urgently needed. Here we evaluated the novel QuantiFERON SARS-CoV-2 assay (Qiagen) measuring INF-ɣ release induced by two spike-derived peptide pools (Ag1 and Ag2) in a cohort of health care workers vaccinated with the mRNA-1273 vaccine and confirmed humoral response. Our study indicates the usefulness of this novel assay for routine laboratories to evaluate cellular immunity against SARS-CoV-2 in response to mRNA-1273 vaccination.

Serological Assays for Assessing Postvaccination SARS-CoV-2 Antibody Response

Serological assays for measuring severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies have crucial applications in the control and surveillance of the current COVID-19 pandemic. A large number of such assays have been developed and are now commercially available. However, there are limited studies evaluating the performance of these tests. We evaluated the performances of the following six commercially available serological assays for detecting SARS-CoV-2 antibodies: (i) Genscript cPass surrogate virus neutralization test (Genscript cPass), (ii) Diasorin-SARS-CoV-2 S1/S2 IgG detection (Diasorin-S1/S2 IgG), (iii) Alinity SARS-CoV-2 IgG II (Alinity IgG II), (iv) Diasorin-SARS-CoV-2 TrimericS IgG (Diasorin-TrimericS IgG), (v) Roche Elecsys anti-SARS-CoV-2-cobas (Roche Elecsys), and (vi) AESKU enzyme linked immunosorbent assay (AESKULISA). The results of these tests were compared against the gold standard plaque reduction neutralization test (PRNT). Roche Elecsys had the highest sensitivity, and the Genscript cPass had the highest specificity. Diasorin-TrimericS IgG had the best overall performance with the highest agreement with the PRNT results. Parallel testing of Genscript cPass with Diasorin-TrimericS IgG and Diasorin-S1/S2 IgG had the optimum performance. Based on the receiver operating characteristic (ROC) curve, lowering the cutoff from 30% to 20% in the Genscript cPass significantly increased the sensitivity and the overall agreement with the PRNT results. Commercially available serological assays are good alternatives to the standard PRNT. However, further studies on larger sample numbers are required for optimization of the assay cutoff values and for evaluation of cost effectiveness. IMPORTANCE Commercial serological assays for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are now widely available. This study adds new knowledge regarding the optimization of these assays for evaluating postvaccination antibodies status. It highlights the positive and negative aspects of each assay in terms of sensitivity, specificity, and positive and negative predictive values, compared to the gold standard neutralization test. When using serological assays to assess postvaccine immune status, a balance of all parameters needs to be considered and not simply the high specificity. This balance is particularly relevant in the current situation where countries are aiming to mass vaccinate their populations and bring this pandemic under control. Assays with good sensitivity will have a lower percentage of false negatives and thus provide confidence for vaccination. Understanding the strengths and limitations of commercially available serological assays is important, not only for better application of these tests but also to understand the immune response and the duration of protection postvaccination.

Emerging SARS-CoV-2 variant B.1.1.7 reduces neutralisation activity of antibodies against wild-type SARS-CoV-2

Spike-specific antibodies contribute significantly to the neutralising activity against SARS-CoV-2 and are important for the therapeutic effect of convalescent plasma. B.1.1.7 is a recently emerged variant of SARS-CoV-2 that has several mutations in the gene encoding for the spike-protein. To assess the potential effect these mutations could have on the neutralising efficacy of antibodies, we evaluated 96 serum samples from convalescent plasma donors collected before the first occurrence of B.1.1.7 and tested their neutralising effect on wild-type SARS-CoV-2 and B.1.1.7. We found that B.1.1.7 is more resistant to neutralisation by convalescent plasma from patients infected with wild-type SARS-CoV-2 with an overall decrease in neutralising activity of 47.7%. Thus, the neutralising effect of convalescent plasma should be determined against the major circulating virus clades whenever possible to ensure the best possible therapeutic effect.

Utility of Different Surrogate Enzyme-Linked Immunosorbent Assays (sELISAs) for Detection of SARS-CoV-2 Neutralizing Antibodies

The plaque reduction neutralization test (PRNT) is a preferred method for the detection of functional, SARS-CoV-2 specific neutralizing antibodies from serum samples. Alternatively, surrogate enzyme-linked immunosorbent assays (ELISAs) using ACE2 as the target structure for the detection of neutralization-competent antibodies have been developed. They are capable of high throughput, have a short turnaround time, and can be performed under standard laboratory safety conditions. However, there are very limited data on their clinical performance and how they compare to the PRNT. We evaluated three surrogate immunoassays (GenScript SARS-CoV-2 Surrogate Virus Neutralization Test Kit (GenScript Biotech, Piscataway Township, NJ, USA), the TECO® SARS-CoV-2 Neutralization Antibody Assay (TECOmedical AG, Sissach, Switzerland), and the Leinco COVID-19 ImmunoRank™ Neutralization MICRO-ELISA (Leinco Technologies, Fenton, MO, USA)) and one automated quantitative SARS-CoV-2 Spike protein-based IgG antibody assay (Abbott GmbH, Wiesbaden, Germany) by testing 78 clinical samples, including several follow-up samples of six BNT162b2 (BioNTech/Pfizer, Mainz, Germany/New York, NY, USA) vaccinated individuals. Using the PRNT as a reference method, the overall sensitivity of the examined assays ranged from 93.8 to 100% and specificity ranged from 73.9 to 91.3%. Weighted kappa demonstrated a substantial to almost perfect agreement. The findings of our study allow these assays to be considered when a PRNT is not available. However, the latter still should be the preferred choice. For optimal clinical performance, the cut-off value of the TECO assay should be individually adapted.

Comparison of Three Serological Methods for the Epidemiological Investigation of TBE in Dogs

Tick-borne encephalitis (TBE) virus is an emerging pathogen that causes severe infections in humans. Infection risk areas are mostly defined based on the incidence of human cases, a method which does not work well in areas with sporadic TBE cases. Thus, sentinel animals may help to better estimate the existing risk. Serological tests should be thoroughly evaluated for this purpose. Here, we tested three test formats to assess the use of dogs as sentinel animals. A total of 208 dog sera from a known endemic area in Southern Germany were tested in an All-Species-ELISA and indirect immunofluorescence assays (IIFA), according to the manufacturer’s instructions. Sensitivity and specificity for both were determined in comparison to the micro-neutralization test (NT) results. Of all 208 samples, 22.1% tested positive in the micro-NT. A total of 18.3% of the samples showed characteristic fluorescence in the IIFA and were, thus, judged positive. In comparison to the micro-NT, a sensitivity of 78.3% and a specificity of 98.8% was obtained. In the ELISA, 19.2% of samples tested positive, with a sensitivity of 84.8% and a specificity of 99.4%. The ELISA is a highly specific test for TBE-antibody detection in dogs and should be well suited for acute diagnostics. However, due to deficits in sensitivity, it cannot replace the NT, at least for epidemiological studies. With even lower specificity and sensitivity, the same applies to IIFA.