Performance Characteristics of the Vidas SARS-CoV-2 IgM and IgG Serological Assays

Analytical measuring interval, linearity, and precision of serology assays for detection of SARS-CoV-2 antibodies according to CLSI guidelines

Serology testing is commonly used to evaluate the immunogenicity of COVID-19 vaccines and measure antibodies as a marker of previous infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In this study, four laboratory-developed serology enzyme-linked immunosorbent assays (SARS-CoV-2 anti-Spike and anti-Nucleocapsid immunoglobin G [IgG] and immunoglobin M [IgM]) calibrated to the WHO International Standard 20/136 were validated via analytical measuring interval (limit of blank [LOB], limit of detection [LOD], and limit of quantification [LOQ]), linearity, and precision according to the Clinical and Laboratory Standards Institute (CLSI) guidelines EP17-A2, EP06 2nd Edition, and EP05-A3. For Spike IgG, LOB was 3.0 binding antibody units per milliliter (BAU/mL), LOD was 4.1 BAU/mL, and LOQ was 27.1 BAU/mL. For Nucleocapsid IgG, LOB was 1.9 BAU/mL, LOD was 3.2 BAU/mL, and LOQ was 24.6 BAU/mL. For Spike IgM, LOB was 57.1 BAU/mL, LOD was 69.0 BAU/mL, and LOQ was 113.5 BAU/mL. For Nucleocapsid IgM, LOD was 242.2 BAU/mL, LOD was 289.9 BAU/mL, and LOQ was 572.4 BAU/mL. Each assay displayed good linearity (max % deviation from linearity (≥LOQ) = 10.7%). The result of within-run repeatability evaluation for medium positive samples was 7.7% for Spike IgG, 4.6% for Nucleocapsid IgG, 7.5% for Spike IgM, and 10.1% for Nucleocapsid IgM. The total precision, including medium positive sample variability across 20 days, three reagent kits, and two operators, was 13.5% for Spike IgG, 14.5% for Nucleocapsid IgG, 17.6% for Spike IgM, and 16.2% for Nucleocapsid IgM. The assays were successfully validated following the applicable CLSI guidelines. All assays met the ±20% deviation from linearity and the ±20% coefficient of variation specification for precision and repeatability.

IMPORTANCE

Reliable and validated serology assays are of increasing importance as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus continues to evolve and cause outbreaks. Validation of serology assays along with calibration to the International and National Standards (such as anti-SARS-CoV-2 Immunoglobulin WHO International Standard 20/136 or Frederick National Laboratory for Cancer Research's National Serology Standard COVID-NS01097) is critical to ensuring that results from clinical studies are reliable and comparable among various assays and laboratories. We describe the design and execution of a comprehensive study that established the analytical measuring intervals, linearity, precision, and repeatability of four in-house developed serology enzyme-linked immunosorbent assays (SARS-CoV-2 anti-Spike immunoglobin G [IgG] and immunoglobin M [IgM] and anti-Nucleocapsid IgG and IgM) following applicable Clinical and Laboratory Standards Institute (CLSI) guidelines. Overall, this study provides practical guidance on experimental design strategies and data analysis techniques, pertaining to the validation of COVID-19 serology assays according to CLSI guidelines, for use in clinical research studies.

Immunogenicity and real-world effectiveness of COVID-19 vaccines in Lebanon: Insights from primary and booster schemes, variants, infections, and hospitalization

In this study, we conducted a case-control investigation to assess the immunogenicity and effectiveness of primary and first booster homologous and heterologous COVID-19 vaccination regimens against infection and hospitalization, targeting variants circulating in Lebanon during 2021-2022. The study population comprised active Lebanese military personnel between February 2021 and September 2022. Vaccine effectiveness (VE) against laboratory-confirmed SARS-CoV-2 infection and associated hospitalization was retrospectively determined during different variant-predominant periods using a case-control study design. Vaccines developed by Sinopharm, Pfizer, and AstraZeneca as well as Sputnik V were analyzed. Prospective assessment of humoral immune response, which was measured based on the SARS-CoV-2 antispike receptor binding domain IgG titer, was performed post vaccination at various time points, focusing on Sinopharm and Pfizer vaccines. Statistical analyses were performed using IBM SPSS and GraphPad Prism. COVID-19 VE remained consistently high before the emergence of the Omicron variant, with lower estimates during the Delta wave than those during the Alpha wave for primary vaccination schemes. However, vaccines continued to offer significant protection against infection. VE estimates consistently decreased for the Omicron variant across post-vaccination timeframes and schemes. VE against hospitalization declined over time and was influenced by the variant. No breakthrough infections progressed to critical or fatal COVID-19. Immunogenicity analysis revealed that the homologous Pfizer regimen elicited a stronger humoral response than Sinopharm, while a heterologous Sinopharm/Pfizer regimen yielded comparable results to the Pfizer regimen. Over time, both Sinopharm's and Pfizer's primary vaccination schemes exhibited decreased humoral immunity titers, with Pfizer being a more effective booster than Sinopharm. This study, focusing on healthy young adults, provides insights into VE during different pandemic waves. Continuous research and monitoring are essential for understanding vaccine-mediated immune responses under evolving circumstances.

Digital Microfluidic Multiplex RT-qPCR for SARS-CoV-2 Detection and Variants Discrimination

Continuous mutations have occurred in the genome of the SARS-CoV-2 virus since the onset of the COVID-19 pandemic. The increased transmissibility of the mutated viruses has not only imposed medical burdens but also prolonged the duration of the pandemic. A point-of-care (POC) platform that provides multitarget detection will help to track and reduce disease transmissions. Here we detected and discriminated three genotypes of SARS-CoV-2, including the wildtype and two variants of concern (VOCs), the Delta variant and Omicron variant, through reverse transcription quantitative polymerase chain reaction (RT-qPCR) on a digital microfluidics (DMF)-based cartridge. Upon evaluating with the RNA samples of Omicron variant, the DMF RT-qPCR presented a sensitivity of 10 copies/μL and an amplification efficiency of 96.1%, capable for clinical diagnosis. When spiking with SARS-CoV-2 RNA (wildtype, Delta variant, or Omicron variant) and 18S rDNA, the clinical analog samples demonstrated accurate detection and discrimination of different SARS-CoV-2 strains in 49 min.

An ultra-sensitive electrochemical biosensor using the Spike protein for capturing antibodies against SARS-CoV-2 in point-of-care

This work presents an innovative ultra-sensitive biosensor having the Spike protein on carbon-based screen-printed electrodes (SPEs), for monitoring in point-of-care antibodies against SARS-CoV-2, a very important tool for epidemiological monitoring of COVID-19 infection and establishing vaccination schemes. In an innovative and simple approach, a highly conductive support is combined with the direct adsorption of Spike protein to enable an extensive antibody capture. The high conductivity was ensured by using carboxylated carbon nanotubes on the carbon electrode, by means of a simple and quick approach, which also increased the surface area. These were then modified with EDC/NHS chemistry to produce an amine layer and undergo Spike protein adsorption, to generate a stable layer capable of capturing the antibodies against SARS-CoV-2 in serum with great sensitivity. Electrochemical impedance spectroscopy was used to evaluate the analytical performance of this biosensor in serum. It displayed a linear response between 1.0 ​pg/mL and 10 ​ng/mL, with a detection limit of ∼0.7 ​pg/mL. The analysis of human positive sera containing antibody in a wide range of concentrations yielded accurate data, correlating well with the reference method. It also offered the unique ability of discriminating antibody concentrations in sera below 2.3 ​μg/mL, the lowest value detected by the commercial method. In addition, a proof-of-concept study was performed by labelling anti-IgG antibodies with quantum dots to explore a new electrochemical readout based on the signal generated upon binding to the anti-S protein antibodies recognised on the surface of the biosensor. Overall, the alternative serologic assay presented is a promising tool for assessing protective immunity to SARS-CoV-2 and a potential guide for revaccination.

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An ultra-sensitive biosensor for detection of low levels of antibodies against SARS-CoV-2.

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Highly conductive substrate with adsorbed protein S and point-of-care capability.

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Application to human sera samples and good correlation with commercial method.

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Electrochemical impedance readings with an iron-based redox probe.

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Alternative electrochemical impedance readings with anti-IgG labelled with quantum dots.

Antibody tests for identification of current and past infection with SARS-CoV-2

BACKGROUND

The diagnostic challenges associated with the COVID-19 pandemic resulted in rapid development of diagnostic test methods for detecting SARS-CoV-2 infection. Serology tests to detect the presence of antibodies to SARS-CoV-2 enable detection of past infection and may detect cases of SARS-CoV-2 infection that were missed by earlier diagnostic tests. Understanding the diagnostic accuracy of serology tests for SARS-CoV-2 infection may enable development of effective diagnostic and management pathways, inform public health management decisions and understanding of SARS-CoV-2 epidemiology.

OBJECTIVES

To assess the accuracy of antibody tests, firstly, to determine if a person presenting in the community, or in primary or secondary care has current SARS-CoV-2 infection according to time after onset of infection and, secondly, to determine if a person has previously been infected with SARS-CoV-2. Sources of heterogeneity investigated included: timing of test, test method, SARS-CoV-2 antigen used, test brand, and reference standard for non-SARS-CoV-2 cases.

SEARCH METHODS

The COVID-19 Open Access Project living evidence database from the University of Bern (which includes daily updates from PubMed and Embase and preprints from medRxiv and bioRxiv) was searched on 30 September 2020. We included additional publications from the Evidence for Policy and Practice Information and Co-ordinating Centre (EPPI-Centre) 'COVID-19: Living map of the evidence' and the Norwegian Institute of Public Health 'NIPH systematic and living map on COVID-19 evidence'. We did not apply language restrictions.

SELECTION CRITERIA

We included test accuracy studies of any design that evaluated commercially produced serology tests, targeting IgG, IgM, IgA alone, or in combination. Studies must have provided data for sensitivity, that could be allocated to a predefined time period after onset of symptoms, or after a positive RT-PCR test. Small studies with fewer than 25 SARS-CoV-2 infection cases were excluded. We included any reference standard to define the presence or absence of SARS-CoV-2 (including reverse transcription polymerase chain reaction tests (RT-PCR), clinical diagnostic criteria, and pre-pandemic samples).

DATA COLLECTION AND ANALYSIS

We use standard screening procedures with three reviewers. Quality assessment (using the QUADAS-2 tool) and numeric study results were extracted independently by two people. Other study characteristics were extracted by one reviewer and checked by a second. We present sensitivity and specificity with 95% confidence intervals (CIs) for each test and, for meta-analysis, we fitted univariate random-effects logistic regression models for sensitivity by eligible time period and for specificity by reference standard group. Heterogeneity was investigated by including indicator variables in the random-effects logistic regression models. We tabulated results by test manufacturer and summarised results for tests that were evaluated in 200 or more samples and that met a modification of UK Medicines and Healthcare products Regulatory Agency (MHRA) target performance criteria.

MAIN RESULTS

We included 178 separate studies (described in 177 study reports, with 45 as pre-prints) providing 527 test evaluations. The studies included 64,688 samples including 25,724 from people with confirmed SARS-CoV-2; most compared the accuracy of two or more assays (102/178, 57%). Participants with confirmed SARS-CoV-2 infection were most commonly hospital inpatients (78/178, 44%), and pre-pandemic samples were used by 45% (81/178) to estimate specificity. Over two-thirds of studies recruited participants based on known SARS-CoV-2 infection status (123/178, 69%). All studies were conducted prior to the introduction of SARS-CoV-2 vaccines and present data for naturally acquired antibody responses. Seventy-nine percent (141/178) of studies reported sensitivity by week after symptom onset and 66% (117/178) for convalescent phase infection. Studies evaluated enzyme-linked immunosorbent assays (ELISA) (165/527; 31%), chemiluminescent assays (CLIA) (167/527; 32%) or lateral flow assays (LFA) (188/527; 36%). Risk of bias was high because of participant selection (172, 97%); application and interpretation of the index test (35, 20%); weaknesses in the reference standard (38, 21%); and issues related to participant flow and timing (148, 82%). We judged that there were high concerns about the applicability of the evidence related to participants in 170 (96%) studies, and about the applicability of the reference standard in 162 (91%) studies. Average sensitivities for current SARS-CoV-2 infection increased by week after onset for all target antibodies. Average sensitivity for the combination of either IgG or IgM was 41.1% in week one (95% CI 38.1 to 44.2; 103 evaluations; 3881 samples, 1593 cases), 74.9% in week two (95% CI 72.4 to 77.3; 96 evaluations, 3948 samples, 2904 cases) and 88.0% by week three after onset of symptoms (95% CI 86.3 to 89.5; 103 evaluations, 2929 samples, 2571 cases). Average sensitivity during the convalescent phase of infection (up to a maximum of 100 days since onset of symptoms, where reported) was 89.8% for IgG (95% CI 88.5 to 90.9; 253 evaluations, 16,846 samples, 14,183 cases), 92.9% for IgG or IgM combined (95% CI 91.0 to 94.4; 108 evaluations, 3571 samples, 3206 cases) and 94.3% for total antibodies (95% CI 92.8 to 95.5; 58 evaluations, 7063 samples, 6652 cases). Average sensitivities for IgM alone followed a similar pattern but were of a lower test accuracy in every time slot. Average specificities were consistently high and precise, particularly for pre-pandemic samples which provide the least biased estimates of specificity (ranging from 98.6% for IgM to 99.8% for total antibodies). Subgroup analyses suggested small differences in sensitivity and specificity by test technology however heterogeneity in study results, timing of sample collection, and smaller sample numbers in some groups made comparisons difficult. For IgG, CLIAs were the most sensitive (convalescent-phase infection) and specific (pre-pandemic samples) compared to both ELISAs and LFAs (P < 0.001 for differences across test methods). The antigen(s) used (whether from the Spike-protein or nucleocapsid) appeared to have some effect on average sensitivity in the first weeks after onset but there was no clear evidence of an effect during convalescent-phase infection. Investigations of test performance by brand showed considerable variation in sensitivity between tests, and in results between studies evaluating the same test. For tests that were evaluated in 200 or more samples, the lower bound of the 95% CI for sensitivity was 90% or more for only a small number of tests (IgG, n = 5; IgG or IgM, n = 1; total antibodies, n = 4). More test brands met the MHRA minimum criteria for specificity of 98% or above (IgG, n = 16; IgG or IgM, n = 5; total antibodies, n = 7). Seven assays met the specified criteria for both sensitivity and specificity. In a low-prevalence (2%) setting, where antibody testing is used to diagnose COVID-19 in people with symptoms but who have had a negative PCR test, we would anticipate that 1 (1 to 2) case would be missed and 8 (5 to 15) would be falsely positive in 1000 people undergoing IgG or IgM testing in week three after onset of SARS-CoV-2 infection. In a seroprevalence survey, where prevalence of prior infection is 50%, we would anticipate that 51 (46 to 58) cases would be missed and 6 (5 to 7) would be falsely positive in 1000 people having IgG tests during the convalescent phase (21 to 100 days post-symptom onset or post-positive PCR) of SARS-CoV-2 infection.

AUTHORS' CONCLUSIONS

Some antibody tests could be a useful diagnostic tool for those in whom molecular- or antigen-based tests have failed to detect the SARS-CoV-2 virus, including in those with ongoing symptoms of acute infection (from week three onwards) or those presenting with post-acute sequelae of COVID-19. However, antibody tests have an increasing likelihood of detecting an immune response to infection as time since onset of infection progresses and have demonstrated adequate performance for detection of prior infection for sero-epidemiological purposes. The applicability of results for detection of vaccination-induced antibodies is uncertain.

Impact of SARS-CoV-2 RBD Mutations on the Production of a Recombinant RBD Fusion Protein in Mammalian Cells

SARS-CoV-2 receptor-binding domain (RBD) is a major target for the development of diagnostics, vaccines and therapeutics directed against COVID-19. Important efforts have been dedicated to the rapid and efficient production of recombinant RBD proteins for clinical and diagnostic applications. One of the main challenges is the ongoing emergence of SARS-CoV-2 variants that carry mutations within the RBD, resulting in the constant need to design and optimise the production of new recombinant protein variants. We describe here the impact of naturally occurring RBD mutations on the secretion of a recombinant Fc-tagged RBD protein expressed in HEK 293 cells. We show that mutation E484K of the B.1.351 variant interferes with the proper disulphide bond formation and folding of the recombinant protein, resulting in its retention into the endoplasmic reticulum (ER) and reduced protein secretion. Accumulation of the recombinant B.1.351 RBD-Fc fusion protein in the ER correlated with the upregulation of endogenous ER chaperones, suggestive of the unfolded protein response (UPR). Overexpression of the chaperone and protein disulphide isomerase PDIA2 further impaired protein secretion by altering disulphide bond formation and increasing ER retention. This work contributes to a better understanding of the challenges faced in producing mutant RBD proteins and can assist in the design of optimisation protocols.

Performance of Elecsys Anti-SARS CoV-2 (Roche) and VIDAS Anti-SARS CoV-2 (Biomérieux) for SARS-CoV-2 Nucleocapsid and Spike Protein Antibody Detection

Introduction

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the novel viral pathogen that causes coronavirus disease 2019 (COVID-19) in humans, has spread worldwide since its identification in late 2019. The pandemic produced an accelerated development of new serological techniques for diagnosis.

Methods

We evaluated two commercial assays for serological diagnosis of SARS-CoV-2 infection, approved by the Administración Nacional de Medicamentos, Alimentos y Tecnología Médica (ANMAT) in Argentina: Elecsys Anti-SARS-CoV-2; Roche for nucleocapsid total antibody detection, and VIDAS Anti-SARS-CoV-2 bioMérieux for spike protein IgG antibody detection. Sensitivity was assessed using a panel of 92 plasma samples from recovered COVID-19 patients who were positive for RT-PCR and positive for neutralizing antibodies by plaque reduction neutralization test (PRNT) and/or positive for IgG antibodies by indirect immunofluorescence assay (IFA). Specificity was determined studying 71 plasma samples collected during year 2018 prior to the COVID-19 pandemic. Assays were evaluated as stand-alone tests.

Results

Sensitivity was 97.8% and 98.9% for the Roche and bioMérieux assays, respectively, specificity: 98.5% (Roche) and 97.1% (bioMérieux), positive predictive value (PPV): 98.9% (Roche) and 97.8% (bioMérieux), and negative predictive value: (NPV) 97.2% (Roche) and 98.5% (bioMérieux). Additionally, Cohen's kappa coefficient demonstrated high concordance (k=0.950) between Roche and bioMérieux.

Discussion

In conclusion, our results evidenced a very good performance for the nucleocapsid antibody assay (Roche) and the spike protein antibody assay (bioMérieux), thus both platforms are equally adequate for indirect diagnosis of SARS-CoV-2 infection through total antibodies and IgG antibody detection, respectively.

Performance evaluation of novel fluorescent-based lateral flow immunoassay (LFIA) for rapid detection and quantification of total anti-SARS-CoV-2 S-RBD binding antibodies in infected individuals

Background

A vast majority of the commercially available lateral flow immunoassay (LFIA) is used to detect SARS-CoV-2 antibodies qualitatively. Recently, a novel fluorescence-based lateral flow immunoassay (LFIA) test was developed for quantitative measurement of the total binding antibody units (BAUs) (BAU/mL) against SARS-CoV-2 spike protein receptor-binding domain (S-RBD).

Aim

This study aimed to evaluate the performance of the fluorescence LFIA Finecare^TM 2019-nCoV S-RBD test along with its reader (Model No.: FS-113).

Methods

Plasma from 150 reverse trancriptase–PCR (RT-PCR)-confirmed positive individuals and 100 prepandemic samples were tested by Fincare^TM to access sensitivity and specificity. For qualitative and quantitative validation of the FinCare^TM measurements, BAU/mL results of FinCare^TM were compared with results of 2 reference assays: the surrogate virus-neutralizing test (sVNT, GenScript Biotech, USA) and the VIDAS®3 automated assay (BioMérieux, France).

Results

Finecare^TM showed 92% sensitivity and 100% specificity compared with PCR. Cohen's Kappa statistic denoted moderate and excellent agreement with sVNT and VIDAS®3, with values being 0.557 (95% CI: 0.32–0.78) and 0.731 (95% CI: 0.51–0.95), respectively. A strong correlation was observed between Finecare^TM/sVNT (r = 0.7, p < 0.0001) and Finecare^TM/VIDAS®3 (r = 0.8, p < 0.0001).

Conclusion

Finecare^TM is a reliable assay and can be used as a surrogate to assess binding and neutralizing antibody response after infection or vaccination, particularly in none or small laboratory settings.

Label-free sensing of virus-like particles below the sub-diffraction limit by wide-field photon state parametric imaging of a gold nanodot array

A parallel four-quadrant sensing method utilizing a specially designed gold nanodot array is created for sensing virus-like particles with a sub-diffraction limit size (∼100 nm) in a wide-field image. Direct label-free sensing of viruses using multiple four-quadrant sensing channels in parallel in a wide-field view enables the possibility of high-throughput onsite screening of viruses.

The association of maternal SARS-CoV-2 vaccination-to-delivery interval and the levels of maternal and cord blood antibodies

OBJECTIVE

To evaluate the correlation of maternal and cord blood levels of SARS-CoV-2 antibodies in pregnant women immunized against COVID-19.

METHODS

A prospective cohort study was performed of pregnant women who delivered at a single university affiliated tertiary medical center. Women who received the COVID-19 vaccine (BNT162b2 Pfizer©) were approached. The correlation between levels of maternal sera and umbilical cord SARS-CoV-2 specific IgG was assessed.

RESULTS

Overall, 58 women were included; of them, 19 had received a single dose and 39 received two doses of the COVID-19 vaccine. Positive levels of umbilical cord IgG were found in 13/19 (68.4%) and 38/39 (97.4%) women after the administration of a single dose and two doses of the vaccine, respectively. The levels of SARS-CoV-2 IgG antibodies in the maternal sera of vaccinated women were positively correlated to their respective concentrations in cord blood sera (ρ = 0.857; R² linear = 0.719; P < 0.001). Thirteen days after vaccination, the ratio of maternal-to-umbilical cord anti Spike IgG antibodies was approximately 1, indicating relatively similar levels in maternal and cord sera.

CONCLUSION

After the SARS-CoV-2 vaccine, levels of maternal and cord blood antibodies were positively correlated, especially when tested after 13 days following administration of the first dose of the vaccine.

Differences in IgG Antibody Responses following BNT162b2 and mRNA-1273 SARS-CoV-2 Vaccines

Studies examining antibody responses by vaccine brand are lacking and may be informative for optimizing vaccine selection, dosage, and regimens. The purpose of this study is to assess IgG antibody responses following immunization with BNT162b2 (30 μg mRNA) and mRNA-1273 (100 μg mRNA) vaccines. A cohort of clinicians at a nonprofit organization is being assessed clinically and serologically following immunization with BNT162b2 or mRNA-1273. IgG responses were measured at the Remington Laboratory by an IgG assay against the SARS-CoV-2 spike protein-receptor binding domain. Mixed-effect linear (MEL) regression modeling was used to examine whether the SARS-CoV-2 IgG level differed by vaccine brand, dosage, or number of days since vaccination. Among 532 SARS-CoV-2 seronegative participants, 530 (99.6%) seroconverted with either vaccine. After adjustments for age and gender, MEL regression modeling revealed that the average IgG antibody level increased after the second dose compared to the first dose (P < 0.001). Overall, titers peaked at week 6 for both vaccines. Titers were significantly higher for the mRNA-1273 vaccine on days 14 to 20 (P < 0.05), 42 to 48 (P < 0.01), 70 to 76 (P < 0.05), and 77 to 83 (P < 0.05) and higher for the BNT162b2 vaccine on days 28 to 34 (P < 0.001). In two participants taking immunosuppressive drugs, the SARS-CoV-2 IgG antibody response remained negative. mRNA-1273 elicited higher IgG antibody responses than BNT162b2, possibly due to the higher S-protein delivery. Prospective clinical and serological follow-up of defined cohorts such as this may prove useful in determining antibody protection and whether differences in antibody kinetics between the vaccines have manufacturing relevance and clinical significance.

IMPORTANCE SARS-CoV-2 vaccines using the mRNA platform have become one of the most powerful tools to overcome the COVID-19 pandemic. mRNA vaccines enable human cells to produce and present the virus spike protein to their immune system, leading to protection from severe illness. Two mRNA vaccines have been widely implemented, mRNA-1273 (Moderna) and BNT162b2 (Pfizer/BioNTech). We found that, following the second dose, spike protein antibodies were higher with mRNA-1273 than with BNT162b2. This is biologically plausible, since mRNA-1273 delivers a larger amount of mRNA (100 μg mRNA) than BNT162b2 (30 μg mRNA), which is translated into spike protein. This difference may need to be urgently translated into changes in the manufacturing process and dose regimens of these vaccines.

Seroconversion in septic ICU patients presenting with COVID-19: necessary but not sufficient

BACKGROUND

As COVID-19 pandemic and vaccination effects progress, research now focuses on adaptive immunological response to SARS-CoV-2. Few studies specifically investigated intensive care unit (ICU) patients, and little is known about kinetics of humoral response in such critically ill patients. In this context, the main objective of the present work was to perform a longitudinal analysis of the humoral response in critically ill COVID-19 patients with prolonged ICU stays in regard with initial inflammatory response, disease severity and mortality.

METHODS

Over a 3 week period, circulating immunoglobulins (Ig) against SARS-CoV-2 along with several immunological and clinical parameters were measured in 64 ICU COVID-19 patients.

RESULTS

Critically ill COVID-19 patients mounted a dynamic and sustained antibody response of both IgM and IgG as soon as the first day of ICU hospitalization. This serological response was not associated with any of the classical immunological parameters measured at ICU admission or with initial severity clinical scores. IgM and IgG levels and seroconversion trajectories were not associated with unfavourable outcome.

CONCLUSION

Despite rapid seroconversion and elevated humoral response, COVID-19 patients are still characterized by elevated mortality. Additional studies, including cytotoxic T cell functions, are mandatory to understand the immunological mechanisms contributing to long stay of COVID-19 patients in ICU.

Prospective Cohort Study of the Kinetics of Specific Antibodies to SARS-CoV-2 Infection and to Four SARS-CoV-2 Vaccines Available in Serbia, and Vaccine Effectiveness: A 3-Month Interim Report

Real-life data on the performance of vaccines against SARS-CoV-2 are still limited. We here present the rates of detection and levels of antibodies specific for the SARS-CoV-2 spike protein RBD (receptor binding domain) elicited by four vaccines available in Serbia, including BNT-162b2 (BioNTech/Pfizer), BBIBP-CorV (Sinopharm), Gam-COVID-Vac (Gamaleya Research Institute) and ChAdOx1-S (AstraZeneca), compared with those after documented COVID-19, at 6 weeks and 3 months post first vaccine dose or post-infection. Six weeks post first vaccine dose, specific IgG antibodies were detected in 100% of individuals fully vaccinated with BNT-162b2 (n = 100) and Gam-COVID-Vac (n = 12) and in 81.7% of BBIBP-CorV recipients (n = 148), while one dose of ChAdOx1-S (n = 24) induced specific antibodies in 75%. Antibody levels elicited by BNT-162b2 were higher, while those elicited by BBIBP-CorV were lower, than after SARS-CoV-2 infection. By 3 months post-vaccination, antibody levels decreased but remained ≥20-fold above the cut-off in BNT-162b2 but not in BBIBP-CorV recipients, when an additional 30% were seronegative. For all vaccines, antibody levels were higher in individuals with past COVID-19 than in naïve individuals. A total of twelve new infections occurred within the first 3 months post-vaccination, eight after the first dose of BNT-162b2 and ChAdOx1-S (one each) and BBIBP-CorV (six), and four after full vaccination with BBIBP-CorV, but none required hospitalization.

Diagnostic accuracy of three SARS-CoV2 antibody detection assays, neutralizing effect and longevity of serum antibodies

Evidence is currently insufficient to know whether SARS-CoV-2 antibodies (Abs) protect from future infection and how long immunity will last. The kinetics of the immune response to SARS-CoV-2 infection and role of serology in estimating individual protective immunity is yet to be established. We evaluated diagnostic performances of three serological assays - Abbott Architect CMIA IgG, bioMerieux VIDAS ELFA IgG/IgM, and Diesse Chorus ELISA IgG/IgM, and analyzed longevity and potential neutralizing effect of SARS-CoV-2 Abs in COVID-19 patients. Clinical sensitivities of assessed IgG tests two to three weeks post symptom onset (PSO) were very high: 96.77 % for Architect, 96.77 % for Chorus, and 100.00 % for VIDAS. Sensitivities of two assessed IgM assays were moderate: 74.07 % for Chorus, and 76.92 % for VIDAS. Specificities were excellent for all assessed IgG assays: 99.01 % for Architect and 100 % for Chorus and VIDAS. Chorus and VIDAS IgM assays also achieved excellent specificity of 99.01 % and 100 %, respectively. In most cases IgG Abs were still present eight months PSO. Neutralizing antibodies were detected in majority of serum samples from convalescent patients. Serum samples from severe COVID-19 patients had higher antibody titers and higher neutralizing activity. We observed a strong positive correlation among SARS-CoV-2 IgG antibody titer and neutralizing activity. The strongest positive correlation to neutralizing activity was found for VIDAS IgG assay.