Harmonization of six quantitative SARS-CoV-2 serological assays using sera of vaccinated subjects

Robust Regression Techniques for Multiple Method Comparison and Transformation

A generalization of Passing-Bablok regression is proposed for comparing multiple measurement methods simultaneously. Possible applications include assay migration studies or interlaboratory trials. When comparing only two methods, the method boils down to the usual Passing-Bablok estimator. It is close in spirit to reduced major axis regression, which is, however, not robust. To obtain a robust estimator, the major axis is replaced by the (hyper-)spherical median axis. This technique has been applied to compare SARS-CoV-2 serological tests, bilirubin in neonates, and an in vitro diagnostic test using different instruments, sample preparations, and reagent lots. In addition, plots similar to the well-known Bland-Altman plots have been developed to represent the variance structure.

The total testing process harmonization: the case study of SARS-CoV-2 serological tests

The total testing process harmonization is central to laboratory medicine, leading to the laboratory test's effectiveness. In this opinion paper the five phases of the TTP are analyzed, describing, and summarizing the critical issues that emerged in each phase of the TTP with the SARS-CoV-2 serological tests that have affected their effectiveness. Testing and screening the population was essential for defining seropositivity and, thus, driving public health policies in the management of the COVID-19 pandemic. However, the many differences in terminology, the unit of measurement, reference ranges and parameters for interpreting results make analytical results difficult to compare, leading to the general confusion that affects or completely precludes the comparability of data. Starting from these considerations related to SARS-CoV-2 serological tests, through interdisciplinary work, the authors have highlighted the most critical points and formulated proposals to make total testing process harmonization effective, positively impacting the diagnostic effectiveness of laboratory tests.

Evaluation of commercial assays for the assessment of SARS-CoV-2 antibody response in hemodialysis patients

BACKGROUND

Hemodialysis patients exhibit variable immunogenicity following administration of the SARS-CoV-2 mRNA vaccine. The aim of the current study was to evaluate the use of two commercial assays in the assessment of SARS-CoV-2 antibody response in hemodialysis patients and to compare their utility to commonly used SARS-CoV-2 serological assays developed in Canada.

METHODS

We evaluated serologic antibody response in 85 hemodialysis patients up to 6 months after receiving both doses of the Pfizer-BioNTech BNT162b2 COVID-19 mRNA vaccine. In addition, antibody response was assessed in 46 chronic kidney disease patients and 40 COVID-19 naïve health care workers (HCW) up to 3 months and 9 months, respectively. Anti-spike (S) and anti-nucleocapsid (N) levels were measured using Elecsys anti-SARS-CoV-2 immunoassays on the Roche analyzer and compared to ELISA-based detection of anti-S, anti-receptor binding domain (RBD), and anti-N.

RESULTS

The Elecsys anti-N immunoassay showed 93 % concordance with the anti-N ELISA. The Elecsys anti-S immunoassay showed 97 % concordance with the anti-S ELISA and 89 % concordance with the anti-RBD ELISA. HCWs exhibited significantly higher anti-S levels relative to hemodialysis patients. Anti-S levels decreased significantly over a 6-month period (p < 0.001) in patients receiving maintenance hemodialysis. In addition, anti-S levels decreased significantly over a 9-month (p < 0.001) and 3-month period (p < 0.001) in HCWs and CKD patients, respectively.

CONCLUSIONS

There is high concordance between commercial SARS-CoV-2 serological assays and SARS-CoV-2 serological assays developed in Canada. Hemodialysis patients exhibited varying immunogenicity following two doses of the COVID-19 mRNA vaccine with anti-S levels decreasing over time.

Hybrid Immunity Provides the Best COVID-19 Humoral Response in Immunocompromised Patients with or without SARS-CoV-2 Infection History

Immunization against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has significantly limited the spread of coronavirus disease 2019 (COVID-19) and reduced the associated complications, especially mortality. To prolong immunity, an immune booster was implemented. We evaluated the role of SARS-CoV-2 infection history in the vaccination schedules of kidney and liver transplant recipients and patients with chronic kidney disease (CKD). To this end, we retrospectively analyzed the data of 78 solid organ transplantation (SOT) recipients and 40 patients with immunoglobulin A (IgA) nephropathy as representatives of the CKD group. Patients received two or three doses of the BNT162b2 vaccine. At the follow-up, antibody (Ab) titer, graft function, COVID-19 history, and patients' clinical condition were assessed. Ab level was higher after two doses in patients with a COVID-19 history over three doses in patients with no COVID-19 history. Compared to three doses, subjects who were administered two doses had a longer median time to infection. Positive antibodies, in response to the third dose, were not observed in up to 8.4% of SOT patients. The results show that the vaccination schedule should take into account the vaccine response rate and COVID-19 history. So-called hybrid immunity appears to be most efficient at providing humoral responses against SARS-CoV-2 infection in immunocompromised patients.

Quality assessment and harmonization of laboratories across Europe for multiple SARS-CoV-2 serology assays

BACKGROUND AND OBJECTIVES

There is a need for conversion of SARS-CoV-2 serology data from different laboratories to a harmonized international unit. We aimed to compare the performance of multiple SARS-CoV-2 antibody serology assays among 25 laboratories across 12 European countries.

MATERIALS AND METHODS

To investigate this we have distributed to all participating laboratories a panel of 15 SARS-CoV-2 plasma samples and a single batch of pooled plasma calibrated to the WHO IS 20/136 standard.

RESULTS

All assays showed excellent discrimination between SARS-CoV-2 seronegative plasma samples and pre-vaccinated seropositive plasma samples but differed substantially in raw antibody titres. Titres could be harmonized to binding antibody units per millilitre by calibration in relation to a reference reagent.

CONCLUSION

The standardization of antibody quantification is of paramount importance to allow interpretation and comparison of serology data reported in clinical trials in order to identify donor cohorts from whom the most effective convalescent plasma can be collected.

Three rounds of a national external quality assessment reveal a link between disharmonic anti-SARS-CoV-2 antibody quantifications and the infection stage

OBJECTIVES

The WHO's standardized measuring unit, "binding antibody units per milliliter (BAU/mL)," should allow the harmonization of quantitative results by different commercial Anti-SARS-CoV-2 immunoassays. However, multiple studies demonstrate inter-assay discrepancies. The antigenic changes of the Omicron variant affect the performance of Spike-specific immunoassays. This study evaluated the variation of quantitative Anti-SARS-CoV-2-Spike antibody measurements among 46, 50, and 44 laboratories in three rounds of a national external quality assessment (EQA) prior to and after the emergence of the Omicron variant in a diagnostic near-to-real-life setting.

METHODS

We analyzed results reported by the EQA participant laboratories from single and sequential samples from SARS-CoV-2 convalescent, acutely infected, and vaccinated individuals, including samples obtained after primary and breakthrough infections with the Omicron variant.

RESULTS

The three immunoassays most commonly used by the participants displayed a low intra-assay and inter-laboratory variation with excellent reproducibility using identical samples sent to the participants in duplicates. In contrast, the inter-assay variation was very high with all samples. Notably, the ratios of BAU/mL levels quantified by different immunoassays were not equal among all samples but differed between vaccination, past, and acute infection, including primary infection with the Omicron variant. The antibody kinetics measured in vaccinated individuals strongly depended on the applied immunoassay.

CONCLUSIONS

Measured BAU/mL levels are only inter-changeable among different laboratories when the same assay was used for their assessment. Highly variable ratios of BAU/mL quantifications among different immunoassays and infection stages argue against the usage of universal inter-assay conversion factors.

Assay Harmonization Study To Measure Immune Response to SARS-CoV-2 Infection and Vaccines: a Serology Methods Study

The Coronavirus disease 2019 (COVID-19) pandemic presented the scientific community with an immediate need for accurate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serology assays, resulting in an expansion of assay development, some without following a rigorous quality control and validation, and with a wide range of performance characteristics. Vast amounts of data have been gathered on SARS-CoV-2 antibody response; however, performance and ability to compare the results have been challenging. This study seeks to analyze the reliability, sensitivity, specificity, and reproducibility of a set of widely used commercial, in-house, and neutralization serology assays, as well as provide evidence for the feasibility of using the World Health Organization (WHO) International Standard (IS) as a harmonization tool. This study also seeks to demonstrate that binding immunoassays may serve as a practical alternative for the serological study of large sample sets in lieu of expensive, complex, and less reproducible neutralization assays. In this study, commercial assays demonstrated the highest specificity, while in-house assays excelled in antibody sensitivity. As expected, neutralization assays demonstrated high levels of variability but overall good correlations with binding immunoassays, suggesting that binding may be reasonably accurate as well as practical for the study of SARS-CoV-2 serology. All three assay types performed well after WHO IS standardization. The results of this study demonstrate there are high performing serology assays available to the scientific community to rigorously dissect antibody responses to infection and vaccination. IMPORTANCE Previous studies have shown significant variability in SARS-CoV-2 antibody serology assays, highlighting the need for evaluation and comparison of these assays using the same set of samples covering a wide range of antibody responses induced by infection or vaccination. This study demonstrated that there are high performing assays that can be used reliably to evaluate immune responses to SARS-CoV-2 in the context of infection and vaccination. This study also demonstrated the feasibility of harmonizing these assays against the International Standard and provided evidence that the binding immunoassays may have high enough correlation with the neutralization assays to serve as a practical proxy. These results represent an important step in standardizing and harmonizing the many different serological assays used to evaluate COVID-19 immune responses in the population.

One-Year Follow-Up of COVID-19 Patients Indicates Substantial Assay-Dependent Differences in the Kinetics of SARS-CoV-2 Antibodies

Determination of antibody levels against the nucleocapsid (N) and spike (S) proteins of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are used to estimate the humoral immune response after SARS-CoV-2 infection or vaccination. Differences in the design and specification of antibody assays challenge the interpretation of test results, and comparative studies are often limited to single time points per patient. We determined the longitudinal kinetics of antibody levels of 145 unvaccinated coronavirus disease 2019 (COVID-19) patients at four visits over 1 year upon convalescence using 8 commercial SARS-CoV-2 antibody assays (from Abbott, DiaSorin, Roche, Siemens, and Technoclone), as well as a virus neutralization test (VNT). A linear regression model was used to investigate whether antibody results obtained in the first 6 months after disease onset could predict the VNT results at 12 months. Spike protein-specific antibody tests showed good correlation to the VNT at individual time points (rS, 0.74 to 0.92). While longitudinal assay comparison with the Roche Elecsys anti-SARS-CoV-2 S test showed almost constant antibody concentrations over 12 months, the VNT and all other tests indicated a decline in serum antibody levels (median decrease to 14% to 36% of baseline). The antibody level at 3 months was the best predictor of the VNT results at 12 months after disease onset. The current standardization to a WHO calibrator for normalization to binding antibody units (BAU) is not sufficient for the harmonization of SARS-CoV-2 antibody tests. Assay-specific differences in absolute values and trends over time need to be considered when interpreting the course of antibody levels in patients. IMPORTANCE Determination of antibodies against SARS-CoV-2 will play an important role in detecting a sufficient immune response. Although all the manufacturers expressed antibody levels in binding antibody units per milliliter, thus suggesting comparable results, we found discrepant behavior between the eight investigated assays when we followed the antibody levels in a cohort of 145 convalescent patients over 1 year. While one assay yielded constant antibody levels, the others showed decreasing antibody levels to a varying extent. Therefore, the comparability of the assays must be improved regarding the long-term kinetics of antibody levels. This is a prerequisite for establishing reliable antibody level cutoffs for sufficient individual protection against SARS-CoV-2.

Design and performance characteristics of the Elecsys anti-SARS-CoV-2 S assay

Background

Automated, high throughput assays are required to quantify the immune response after infection with or vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This study on the Roche Elecsys^® Anti-SARS-CoV-2 S (ACOV2S) assay provides insights on the assay design and performance.

Methods

The ACOV2S assay quantifies antibodies to the receptor-binding domain of the SARS-CoV-2 spike protein. The assigned units and the underlying standardization were compared to the international reference standard in BAU/mL. Assay specificity was assessed in samples (n=5981) collected prior to the COVID-19 pandemic and in samples from patients with non-COVID-19 respiratory infections (n=697) or other infectious diseases (n=771). Sensitivity was measured in 1313 samples from patients with mild COVID-19 and 297 samples from patients hospitalized with COVID-19. Comparison of results was performed to a comparator semi-quantitative anti-S1 assay of indirect detection format as well as a commercially available and an in-house version of a surrogate neutralization assay (ACE2-RBD).

Results

The originally assigned units for the ACOV2S assay were shown to be congruent to the units of the First International WHO Standard for anti-SARS-CoV-2 immunoglobulins. Overall specificity was 99.98% with no geographical differences noted and no loss of specificity in samples containing potentially cross-reacting antibodies. High sensitivity was observed, with 98.8% of samples reported to be reactive >14 days after infection and sustained detection of antibodies over time. For all samples, ACOV2S titers and neutralization capacities developed with comparable dynamics. Robust standardization and assay setup enable excellent reproducibility of results, independent of lot or analyzer used.

Conclusion

The results from this study confirmed that ACOV2S is a highly sensitive and specific assay and correlates well with surrogate neutralization assays. The units established for ACOV2S are also interchangeable with the units of the First International WHO Standard for anti-SARS-CoV-2 immunoglobulins. Worldwide availability of the assay and analyzers render ACOV2S a highly practical tool for population-wide assessment and monitoring of the humoral response to SARS-CoV-2 infection or vaccination.

Non-Myelofibrosis Chronic Myeloproliferative Neoplasm Patients Show Better Seroconversion Rates after SARS-CoV-2 Vaccination Compared to Other Hematologic Diseases: A Multicentric Prospective Study of KroHem

Disease- and treatment-mediated immunodeficiency might render SARS-CoV-2 vaccines less effective in patients with hematologic diseases. We performed a prospective non-interventional study to evaluate humoral response after one and two doses of mRNA-1273, BNT162b2, or ChAdOx1 nCoV-19 vaccine in 118 patients with different malignant or non-malignant hematologic diseases from three Croatian treatment centers. An electrochemiluminescent assay was used to measure total anti-SARS-CoV-2 S-RBD antibody titers. After one vaccine dose, 20/66 (33%) achieved seropositivity with a median antibody titer of 6.1 U/mL. The response rate (58/90, 64.4%) and median antibody titer (>250 U/mL) were higher after two doses. Seropositivity varied with diagnosis (overall p < 0.001), with the lowest rates in lymphoma (34.6%) and chronic lymphocytic leukemia (52.5%). The overall response rate in chronic myeloproliferative neoplasms (CMPN) was 81.3% but reached 100% in chronic myeloid leukemia and other non-myelofibrosis CMPN. At univariable analysis, age > 67 years, non-Hodgkin’s lymphoma, active treatment, and anti-CD20 monoclonal antibody therapy increased the likelihood of no vaccine response, while hematopoietic stem cell recipients were more likely to respond. Age and anti-CD20 monoclonal antibody therapy remained associated with no response in a multivariable model. Patients with the hematologic disease have attenuated responses to SARS-CoV-2 vaccines, and significant variations in different disease subgroups warrant an individualized approach.

Longitudinal dynamics of SARS-CoV-2 anti-receptor binding domain IgG antibodies in a wide population of health care workers after BNT162b2 vaccination

OBJECTIVES

With the availability of vaccines, commercial assays detecting anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies evolved toward quantitative assays directed to the spike glycoprotein or its receptor-binding domain (RBD). The objective was to perform a large-scale, longitudinal study involving health care workers (HCWs), with the aim of establishing the kinetics of immune response throughout the 9-month period after receipt of the second dose of the BNT162b2 vaccine.

METHODS

Quantitative determination of immunoglobulin (Ig) G antibodies against the RBD of the S1 subunit of the spike protein of SARS-CoV-2 on the Alinity systems.

RESULTS

The highest levels of anti-RBD IgG were measured after 1 month from full vaccination (median: 1432 binding antibody units/ml [BAU/ml]); subsequently, a steep decrease (7.4-fold decrease) in IgG levels was observed at 6 months (median: 194.3 BAU/ml), with a further 2.5-fold decrease at 9 months (median: 79.3 BAU/ml). Furthermore, the same data, when analyzed for sex, showed significant differences between male and female participants at both 1 and 9 months from vaccination, but not at 6 months.

CONCLUSION

Our results confirm the tendency of anti-RBD antibodies to decrease over time, also when extending the analysis up to 9 months, and highlight a better ability of the female sex to produce antibodies 1 month and 9 months after vaccination. Overall, these data, obtained in a wide population of HCWs, support the importance of having increased the vaccine doses.

Smart Immunosensors for Point-of-Care Serological Tests Aimed at Assessing Natural or Vaccine-Induced SARS-CoV-2 Immunity

Innovative and highly performing smart voltammetric immunosensors for rapid and effective serological tests aimed at the determination of SARS-CoV-2 antibodies were developed and validated in human serum matrix. Two immunosensors were developed for the determination of immunoglobulins directed against either the nucleocapsid or the spike viral antigen proteins. The immunosensors were realized using disposable screen-printed electrodes modified with nanostructured materials for the immobilization of the antigens. Fast quantitative detection was achieved, with analysis duration being around 1 h. Signal readout was carried out through a smart, compact and battery-powered potentiostat, based on a Wi-Fi protocol and devised for the Internet of Things (IoT) paradigm. This device is used for the acquisition, storage and sharing of clinical data. Outstanding immunosensors' sensitivity, specificity and accuracy (100%) were assessed, according to the diagnostic guidelines for epidemiological data. The overall performance of the sensing devices, combined with the portability of the IoT-based device, enables their suitability as a high-throughput diagnostic tool. Both of the immunosensors were validated using clinical human serum specimens from SARS-CoV-2 infected patients, provided by IRCCS Ospedale San Raffaele.

Health technology assessment to employ COVID-19 serological tests as companion diagnostics in the vaccination campaign against SARS-CoV-2

OBJECTIVES

In scenarios of vaccine scarcity or contexts of organizational complexity, it is necessary to define prioritization strategies for allocating vaccine doses in compliance with the criterion of equity and efficiency of health resources. In this context, the COVIDIAGNOSTIX project, based on the health technology assessment (HTA), assessed the role of SARS-CoV-2 serological tests as a companion diagnostic in the definition of the vaccination strategies for the vaccine administration. To guarantee evidence support for health policy choices, two different vaccine strategies were analyzed, one based on administering the vaccine booster dose to the entire population (VACCINE strategy) and the other based on allocation criteria (TEST&VACCINE strategy).

METHODS

The decision-oriented HTA (DoHTA) method, integrated with specific modeling and simulation techniques, helped define the perimeter to make health policy choices.

RESULTS

The processing of the scores attributed to the key performance indicators concerning all the evaluation domains shows a performance of 94.34% for the TEST&VACCINE strategy and 83.87% for the VACCINE strategy.

CONCLUSIONS

TEST&VACCINE strategy can be the most advantageous in various scenarios due to greater speed from an operational and an economic point of view. The assessment schemes defined by COVIDIAGNOSTIX (i.e., technologies/intended use/settings) can easily and quickly be exported and adapted to respond to similar health "policy questions".

IgG Anti-Spike Antibodies and Surrogate Neutralizing Antibody Levels Decline Faster 3 to 10 Months After BNT162b2 Vaccination Than After SARS-CoV-2 Infection in Healthcare Workers

Background

IgG anti-spike (S) antibodies arise after SARS-CoV-2 infection as well as vaccination. Levels of IgG anti-S are linked to neutralizing antibody titers and protection against (re)infection.

Methods

We measured IgG anti-S and surrogate neutralizing antibody kinetics against Wild Type (WT) and 4 Variants of Concern (VOC) in health care workers (HCW) 3 and 10 months after natural infection ("infection", n=83) or vaccination (2 doses of BNT162b2) with ("hybrid immunity", n=17) or without prior SARS-CoV-2 infection ("vaccination", n=97).

Results

The humoral immune response in the "vaccination" cohort was higher at 3 months, but lower at 10 months, compared to the "infection" cohort due to a faster decline. The "hybrid immunity" cohort had the highest antibody levels at 3 and 10 months with a slower decline compared to the "vaccination" cohort. Surrogate neutralizing antibody levels (expressed as %inhibition of ACE-2 binding) showed a linear relation with log10 of IgG anti-S against WT and four VOC. IgG anti-S corresponding to 90% inhibition ranged from 489 BAU/mL for WT to 1756 BAU/mL for Beta variant. Broad pseudoneutralization predicted live virus neutralization of Omicron BA.1 in 20 randomly selected high titer samples.

Conclusions

Hybrid immunity resulted in the strongest humoral immune response. Antibodies induced by natural infection decreased more slowly than after vaccination, resulting in higher antibody levels at 10 months compared to vaccinated HCW without prior infection. There was a linear relationship between surrogate neutralizing activity and log10 IgG anti-S for WT and 4 VOC, although some VOC showed reduced sensitivity to pseudoneutralization.

Cellular and Humoral Immune Responses and Breakthrough Infections After Two Doses of BNT162b Vaccine in Healthcare Workers (HW) 180 Days After the Second Vaccine Dose

Background

Immunity and clinical protection induced by mRNA vaccines against SARS-CoV-2 have been shown to decline overtime. To gather information on the immunity profile deemed sufficient in protecting against hospitalization, we tested IgG levels, interferon-gamma (IFN-γ) secretion, and neutralizing antibodies 180 days (d180) after the second shot of BNT162b vaccine, in HW.

Methods

A total of 392 subjects were enrolled. All received BioNTech/Pfizer from February 2020 to April 2021. The vaccine-specific humoral response was quantitatively determined by testing for IgG anti-S1 domain of SARS-CoV-spike protein. Live virus microneutralization (MN) was evaluated by an assay performing incubation of serial 2-fold dilution of human serum samples, starting from 1:10 to 1:5120, with an equal volume of Wuhan strain and Delta VOC viral solution and assessing the presence/absence of a cytopathic effect. SARS-CoV-2-spike protein-specific T-cell response was determined by a commercial IFN-γ release assay.

Results

In 352 individuals, at d180, IgG levels decreased substantially but no results below the assay's positivity threshold were observed. Overall, 22 naive (8.1%) had values above the highest threshold. Among COVID-naive, the impact of age, which was observed at earlier stages, disappeared at d180, while it remained significant for 81 who had experienced a previous infection. Following the predictive model of protection by Khoury, we transformed the neutralizing titers in IU/ml and used a 54 IU/ml threshold to identify subjects with 50% protective immunity. Overall, live virus MN showed almost all subjects with previous exposure to SARS-CoV-2 neutralized the virus as compared to 33% of naive double-dosed subjects (p < 0.0001). All previously exposed subjects had strong IFN-γ secretion (>200 mIU/ml); among 271 naive, 7 (2.58%) and 17 (6.27%) subjects did not show borderline or strong secretion, respectively.

Conclusions

In naive subjects, low IgG titers are relatively long-lasting. Only a third of naive subjects maintain neutralizing responses. After specific stimulation, a very limited number of naive were unable to produce IFN-γ. The results attained in the small group of subjects with breakthrough infection suggest that simultaneous neutralizing antibody titers <20, binding antibody levels/ml <200, and IFN-γ <1,000 mIU/ml in subjects older than 58 may identify at-risk groups.

Exploratory assessment of serological tests to determine antibody titer against SARS-CoV-2: Appropriateness and limits

BACKGROUND

Serological tests can be used to detect antibodies in the serum of subject's after SARS-CoV-2 infection and vaccination. Currently, variability in antibody titers and the availability of a multiplicity of serological tests have made it necessary to highlight their appropriateness and limitations in various diagnostic settings.

METHODS

This study is part of Covidiagnostix, a multicenter project aimed at the assessment of the health technology used in SARS-CoV-2 serological tests. Based on data gained from the analysis of over 5000 subjects, a selected number of serum samples, representative of different diagnostic settings, were analyzed first by qualitative immunoassays (IgA, M, and G MILLIPLEX^® SARS-CoV-2 tests based on Luminex^® ) to define the immunoglobulins serum composition and subsequently by four serological diagnostic tests (Elecsys Anti-SARS-CoV-2 and Elecsys Anti-SARS-CoV-2 S by Roche, SARS-CoV-2 IgG by Siemens Healthcare, and CHORUS SARS-CoV-2 "NEUTRALIZING" Ab by DIESSE). The first WHO International Standard for SARS-CoV-2 was also analyzed using the same methods.

RESULTS

This study evaluated the antibody content and titer of the WHO Standard and serum of subjects with/without previous infection and before/after vaccination for SARS-CoV-2.

CONCLUSION

The definition of antibodies in the WHO standard and the analysis of serum samples allowed for the identification of the appropriateness of serological tests in each diagnostic setting, increasing the effectiveness of the resulting laboratory data. Furthermore, we found that it would be optimal to produce new international standards against the S1 domain and RBD of the SARS-CoV-2 spike protein for a more effective serological monitoring of vaccination.

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.

Investigating phenotypes of pulmonary COVID-19 recovery - a longitudinal observational prospective multicenter trial

Background:

The optimal procedures to prevent, identify, monitor, and treat long-term pulmonary sequelae of COVID-19 are elusive. Here, we characterized the kinetics of respiratory and symptom recovery following COVID-19.

Methods:

We conducted a longitudinal, multicenter observational study in ambulatory and hospitalized COVID-19 patients recruited in early 2020 (n = 145). Pulmonary computed tomography (CT) and lung function (LF) readouts, symptom prevalence, and clinical and laboratory parameters were collected during acute COVID-19 and at 60, 100, and 180 days follow-up visits. Recovery kinetics and risk factors were investigated by logistic regression. Classification of clinical features and participants was accomplished by unsupervised and semi-supervised multiparameter clustering and machine learning.

Results:

At the 6-month follow-up, 49% of participants reported persistent symptoms. The frequency of structural lung CT abnormalities ranged from 18% in the mild outpatient cases to 76% in the intensive care unit (ICU) convalescents. Prevalence of impaired LF ranged from 14% in the mild outpatient cases to 50% in the ICU survivors. Incomplete radiological lung recovery was associated with increased anti-S1/S2 antibody titer, IL-6, and CRP levels at the early follow-up. We demonstrated that the risk of perturbed pulmonary recovery could be robustly estimated at early follow-up by clustering and machine learning classifiers employing solely non-CT and non-LF parameters.

Conclusions:

The severity of acute COVID-19 and protracted systemic inflammation is strongly linked to persistent structural and functional lung abnormality. Automated screening of multiparameter health record data may assist in the prediction of incomplete pulmonary recovery and optimize COVID-19 follow-up management.

Funding:

The State of Tyrol (GZ 71934), Boehringer Ingelheim/Investigator initiated study (IIS 1199-0424).

Clinical trial number:

ClinicalTrials.gov: NCT04416100

Differential Dynamics of SARS-CoV-2 Binding and Functional Antibodies upon BNT162b2 Vaccine: A 6-Month Follow-Up

To investigate the dynamic association among binding and functional antibodies in health-care-workers receiving two doses of BNT162b2 mRNA COVID-19-vaccine, SARS-CoV-2 anti-RBD IgG, anti-Trimeric-S IgG, and neutralizing antibodies (Nabs) were measured in serum samples collected at 2 weeks, 3 months, and 6 months from full vaccination. Despite the high correlation, results for anti-RBD and anti-Trimeric S IgG were numerically different even after recalculation to BAU/mL following WHO standards indications. Moreover, after a peak response at 2 weeks, anti-RBD IgG levels showed a 4.5 and 13 fold decrease at 3 and 6 months, respectively, while the anti-Trimeric S IgG presented a less pronounced decay of 2.8 and 4.7 fold. Further different dynamics were observed for Nabs titers, resulting comparable at 3 and 6 months from vaccination. We also demonstrated that at NAbs titers ≥40, the area under the receiver operating characteristic curve and the optimal cutoff point decreased with time from vaccination for both anti-RBD and anti-Trimeric S IgG. The mutating relation among the anti-RBD IgG, anti-Trimeric S IgG, and neutralizing antibodies are indicative of antibody maturation upon vaccination. The lack of standardized laboratory procedures is one factor interfering with the definition of a correlate of protection from COVID-19.

Immunological Biomarkers in Blood to Monitor the Course and Therapeutic Outcomes of COVID-19

BACKGROUND

The COVID-19 pandemic has posed a great challenge to the medical community because little is known about its clinical course, therapeutic options, and laboratory monitoring tools for diagnosis, prognosis, and surveillance. This review focuses on immune biomarkers that can be measured in peripheral blood in a clinical laboratory under routine conditions to monitor the innate immune system response in the acute phase, as well as the adaptive immune response established both after infection and vaccination.

METHODS

A PubMed search was performed covering January 2020 to June 2021 to extract biomarkers suitable for monitoring the immune response and outcome of COVID-19 and therapeutic interventions, including vaccination.

RESULTS

To monitor the innate immune response, cytokines such as interleukin-6 or acute phase reactants such as C-reactive protein or procalcitonin can be measured on autoanalyzers complemented by automated white blood cell differential counts. The adaptive immune response can be followed by commercially available enzyme-linked immune spot assays to assess the specific activation of T cells or by monitoring immunoglobulin A (IgA), IgM, and IgG antibodies in serum to follow B-cell activation. As antigens of the SARS-CoV-2 virus, spike and nucleocapsid proteins are particularly suitable and allow differentiation between the immune response after infection or vaccination.

CONCLUSIONS

Routine immune monitoring of COVID-19 is feasible in clinical laboratories with commercially available instruments and reagents. Strategies such as whether biomarkers reflecting the response of the innate and adaptive immune system can be used to make predictions and assist in individualizing therapeutic interventions or vaccination strategies need to be determined in appropriate clinical trials. Promising preliminary data are already available based on single-center reports and completed or ongoing vaccination trials.

Longitudinal comparison of automated SARS-CoV-2 serology assays in assessing virus neutralization capacity in COVID-19 convalescent sera

CONTEXT.–

Serological tests on automated immunology analyzers are increasingly used to monitor the acquired immunity against SARS-CoV-2. The heterogeneity of assays raises concerns about their diagnostic performance and comparability.

OBJECTIVE.–

To test sera from formerly infected individuals for SARS-Cov-2 antibodies utilizing six automated serology assays and a pseudoneutralization test (PNT).

DESIGN.–

Six SARS-CoV-2 serology assays were utilized to assess 954 samples collected during a 12 months period from 315 COVID-19 convalescents. The tests determined either antibodies against the viral nucleocapsid (anti-NC) or spike protein (anti-S). Two assays did not distinguish between antibody classes whereas the others selectively measured immunoglubulins G (IgG) antibodies. PNT was used to detect the presence of neutralizing antibodies.

RESULTS.–

Comparison of qualitative results showed only slight to moderate concordance between the assays (Cohen's kappa < 0.57). Significant correlations (P < .001) were observed between the antibody titers from all quantitative assays. However, titer changes were not detected equally. A total anti-S assay measured an increase in 128 out of 172 cases (74%) of a suitable subset, whereas all IgG anti-S tests reported decreases in at least 118 (69%). Regarding the PNT results, diagnostic sensitivities ≥89% were achieved with PPVs ≥93%. In contrast, specificity changed substantially over time varying from 20 to 100%.

CONCLUSIONS.–

Comparability of serological SARS-CoV-2 antibody tests is rather poor. Due to different diagnostic specificities, the tested assays were not equally capable of capturing changes in antibody titers. However, with thoroughly validated cut-offs, IgG-selective anti-S assays are a reliable surrogate test for SARS-CoV-2 neutralizing antibodies in former COVID-19 patients.

Antibody response induced by the boost overdose during COVID-19 heterologous prime-boost vaccination strategy

BACKGROUND

Measurement of anti-SARS-CoV-2 RBD Ig G antibody response is very important to define the dynamics of immunization in vaccine COVID-19 recipients.

MATERIALS AND METHODS

Sera from four BNT162b2 vaccine recipients who erroneously received vaccine overdose were analyzed at different time-points.

RESULTS

At 6 days the serum increase of antibodies was analogous for the three SARS-CoV-2 naïve recipients. At 14 days the antibody level increased and reached a peak, though showing a different pattern among the three recipients. At 21 days the serum antibody level started to decrease from its maximum value. The data for the previously infected recipient were in agreement with values found in COVID-19 positive receivers. Thus, the prime-dose of vaccine was enough to elicit a significant antibody response.

CONCLUSIONS

In spite of the overdosage, this study confirms the efficiency of the BNT162b vaccine in eliciting a sustained antibody response as heterologous boost-vaccine in previously Oxford/AstraZeneca vaccinated recipients, as well as, prime-vaccine in COVID-19 infected receivers. Importantly, the humoral immune response of recipients was not proportional to the vaccine overdose. Nonetheless, we cannot portray a univocal effect of vaccine overdose concerning anti-SARS-CoV-2 antibody response because the values found were highly heterogeneous.

Antibody Titer Kinetics and SARS-CoV-2 Infections Six Months after Administration with the BNT162b2 Vaccine

Background: Studies reporting the long-term humoral response after receiving the BNT162b2 COVID-19 vaccine are important to drive future vaccination strategies. Yet, available literature is scarce. Covidiagnostix is a multicenter study designed to assess the antibody response in >1000 healthcare professionals (HCPs) who received the BNT162b2 vaccine. Methods: Serum was tested at time-0 (T₀), before the first dose, T₁, T_2, and T₃, respectively, 21, 42, and 180 days after T₀. Antibodies against the SARS-CoV-2 nucleocapsid-protein were measured to assess SARS-CoV-2 infections, whereas antibodies against the receptor-binding domain of the spike protein were measured to assess the vaccine response. Neutralization activity against the D614G, B.1.1.7, and B.1.351 variants were also analyzed. Results: Six months post-vaccination HCPs showed an antibody titer decrease of approximately 70%, yet, the titer was still one order of magnitude higher than that of seropositive individuals before vaccination. We identified 12 post-vaccination infected HCPs. None showed severe symptoms. Interestingly, most of them showed titers at T₂ above the neutralization thresholds obtained from the neutralization activity experiments. Conclusion: Vaccination induces a humoral response which is well detectable even six months post-vaccination. Vaccination prevents severe COVID-19 cases, yet post-vaccination infection is possible even in the presence of a high anti-S serum antibody titer.

Waning of IgG, Total and Neutralizing Antibodies 6 Months Post-Vaccination with BNT162b2 in Healthcare Workers

Data about the long-term duration of antibodies after SARS-CoV-2 vaccination are still scarce and are important to design vaccination strategies. In this study, 231 healthcare professionals received the two-dose regimen of BNT162b2. Of these, 158 were seronegative and 73 were seropositive at baseline. Samples were collected at several time points. The neutralizing antibodies (NAbs) and antibodies against the nucleocapsid and the spike protein of SARS-CoV-2 were measured. At day 180, a significant antibody decline was observed in seronegative (-55.4% with total antibody assay; -89.6% with IgG assay) and seropositive individuals (-74.8% with total antibody assay; -79.4% with IgG assay). The estimated half-life of IgG from the peak humoral response was 21 days (95% CI: 13-65) in seronegative and 53 days (95% CI: 40-79) in seropositive individuals. The estimated half-life of total antibodies was longer and ranged from 68 days (95% CI: 54-90) to 114 days (95% CI: 87-167) in seropositive and seronegative individuals, respectively. The decline of NAbs was more pronounced (-98.6%) and around 45% of the subjects tested were negative at day 180. Whether this decrease correlates with an equivalent drop in the clinical effectiveness against the virus would require appropriate clinical studies.