Detection of IgM and IgG antibodies in patients with coronavirus disease 2019

Humoral immunological kinetics of severe acute respiratory syndrome coronavirus 2 infection and diagnostic performance of serological assays for coronavirus disease 2019: an analysis of global reports

As the coronavirus disease 2019 (COVID-19) pandemic continues to rise and second waves are reported in some countries, serological test kits and strips are being considered to scale up an adequate laboratory response. This study provides an update on the kinetics of humoral immune response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and performance characteristics of serological protocols (lateral flow assay [LFA], chemiluminescence immunoassay [CLIA] and ELISA) used for evaluations of recent and past SARS-CoV-2 infection. A thorough and comprehensive review of suitable and eligible full-text articles was performed on PubMed, Scopus, Web of Science, Wordometer and medRxiv from 10 January to 16 July 2020. These articles were searched using the Medical Subject Headings terms 'COVID-19', 'Serological assay', 'Laboratory Diagnosis', 'Performance characteristics', 'POCT', 'LFA', 'CLIA', 'ELISA' and 'SARS-CoV-2'. Data from original research articles on SARS-CoV-2 antibody detection ≥second day postinfection were included in this study. In total, there were 7938 published articles on humoral immune response and laboratory diagnosis of COVID-19. Of these, 74 were included in this study. The detection, peak and decline period of blood anti-SARS-CoV-2 IgM, IgG and total antibodies for point-of-care testing (POCT), ELISA and CLIA vary widely. The most promising of these assays for POCT detected anti-SARS-CoV-2 at day 3 postinfection and peaked on the 15th day; ELISA products detected anti-SARS-CoV-2 IgM and IgG at days 2 and 6 then peaked on the eighth day; and the most promising CLIA product detected anti-SARS-CoV-2 at day 1 and peaked on the 30th day. The most promising LFA, ELISA and CLIA that had the best performance characteristics were those targeting total SARS-CoV-2 antibodies followed by those targeting anti-SARS-CoV-2 IgG then IgM. Essentially, the CLIA-based SARS-CoV-2 tests had the best performance characteristics, followed by ELISA then POCT. Given the varied performance characteristics of all the serological assays, there is a need to continuously improve their detection thresholds, as well as to monitor and re-evaluate their performances to assure their significance and applicability for COVID-19 clinical and epidemiological purposes.

Patterns of neutralizing humoral response to SARS-CoV-2 infection among hematologic malignancy patients reveal a robust immune response in anti-cancer therapy-naive patients

Understanding antibody-based SARS-CoV-2 immunity in hematologic malignancy (HM) patients following infection is crucial to inform vaccination strategies for this highly vulnerable population. This cross-sectional study documents the anti-SARS-CoV-2 humoral response and serum neutralizing activity in 189 HM patients recovering from a PCR-confirmed infection. The overall seroconversion rate was 85.7%, with the lowest values in patients with lymphoid malignancies or undergoing chemotherapy. Therapy-naive patients in the "watch and wait" status were more likely to seroconvert and display increased anti-s IgG titers. Enhanced serum neutralizing activity was observed in the following SARS-CoV-2-infected HM patient groups: (i) males; (ii) severe COVID-19; and (iii) "watch and wait" or "complete/partial response". The geometric mean (GeoMean) ID50 neutralization titers in patients analyzed before or after 6 months post-infection were 299.1 and 306.3, respectively, indicating that >50% of the patients in either group had a neutralization titer sufficient to provide 50% protection from symptomatic COVID-19. Altogether, our findings suggest that therapy-naive HM patients mount a far more robust immune response to SARS-CoV-2 infection vs. patients receiving anti-cancer treatment, raising the important question as to whether HM patients should be vaccinated before therapy and/or receive vaccine formats capable of better recapitulating the natural infection.

Rapid field determination of SARS-CoV-2 by a colorimetric and fluorescent dual-functional lateral flow immunoassay biosensor

The rapid and accurate diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at the early stage of virus infection can effectively prevent the spread of the virus and control the epidemic. Here, a colorimetric and fluorescent dual-functional lateral flow immunoassay (LFIA) biosensor was developed for the rapid and sensitive detection of spike 1 (S1) protein of SARS-CoV-2. A novel dual-functional immune label was fabricated by coating a single-layer shell formed by mixing 20 nm Au nanoparticles (Au NPs) and quantum dots (QDs) on SiO₂ core to produce strong colorimetric and fluorescence signals and ensure good monodispersity and high stability. The colorimetric signal was used for visual detection and rapid screening of suspected SARS-CoV-2 infection on sites. The fluorescence signal was utilized for sensitive and quantitative detection of virus infection at the early stage. The detection limits of detecting S1 protein via colorimetric and fluorescence functions of the biosensor were 1 and 0.033 ng/mL, respectively. Furthermore, we evaluated the performance of the biosensor for analyzing real samples. The novel biosensor developed herein had good repeatability, specificity and accuracy, which showed great potential as a tool for rapidly detecting SARS-CoV-2.

Detection of IgG and IgM Levels in Patients with COVID-19 in Mosul Province, Iraq

The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) has become the most dangerous viral infection worldwide. Since its identification in late 2019, the number of medical trials to combat the infection has sharply increased. Here, we investigated the profiles of IgG and IgM in 85 patients with confirmed SARS-CoV-2 infection from day 1 after symptom onset until day 35 with 5-day intervals. Serum samples were collected and stored until use. We observed that IgM levels were detectable on day 5 post symptom onset and increased sharply, with the highest rate detected in moderate cases (32.332 ± 4.32, n=10). Subsequently, a significant reduction in IgM was observed until it was undetectable on day 35 after symptom onset. Meanwhile, IgG levels were detected on day 10 post symptom onset, and the highest rate was observed in moderate cases (8.232 ± 2.3, n=10). A significant increase in IgG rate was observed in all patients, with the highest rate in moderate cases (42.432 ± 4.34, n=67) on day 35 post symptom onset. The statistical difference between the case and control groups was significant (p≤0.001). Two out of 85 patients died during the study.

Comparison of COVID-19 laboratory diagnosis by commercial kits: Effectivity of RT-PCR to the RT-LAMP

Coronavirus disease 2019 or COVID-19 caused by novel coronavirus/severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2 or 2019-nCoV) is an ongoing pandemic that has emerging global effects and requires rapid and reliable diagnostic testing. Quantitative reverse transcription-polymerase chain reaction (q-RT-PCR) is the gold standard method for SARS-CoV-2 detections. On the other hand, new approaches remedy the diagnosis difficulties gradually. Reverse transcription loop-mediated isothermal amplification (RT-LAMP) as one of these novel approaches may also contribute to faster and cheaper field-based testing. The present study was designed to evaluate this rapid screening diagnostic test that can give results in 30-45 min and to compare the effectiveness of LAMP to the q-RT-PCR. The 30 randomly chosen patient samples were generated by nasopharyngeal swabs with a portion of the SARS-CoV-2 nucleic sequence. The sample of quantification cycle (Cq) values was tested using RT-LAMP as well as by conventional q-RT-PCR. The patient samples were tested with four different kits (SENSObiz COVID-19 [SARS-CoV-2] LAMP Assay, the QIAseq DIRECT SARS-CoV-2 kit, Biospeedy SARS-CoV-2 Variant Plus kit, and CoVirion-CV19-2 SARS-CoV-2 OneStep RT-PCR kit) and two different PCR devices (GDS Rotor-Gene Q Thermocycler and Inovia Technologies GenX series). Based on 30 patient samples, the positive/negative ratio (P/N) was 30/0 as Biospeedy and Covirion (positivity 100%), 28/2 as Qiagen kit (positivity 93.3%) for the samples studied on the Inovia device while the same samples on the Rotor-Gene device were 30/0 as Biospeedy and Covirion (positivity 100%), 29/1 as Qiagen kit at the first day (96.7%). On the fifth day, the samples were studied in the Inovia device and the respective results were obtained: 27/3 as Biospeedy (positivity 90%), 16/14 as Qiagen (positivity 53.3%), 28/2 as Covirion kit (positivity 93.3%). When these samples were studied in the Rotor-Gene device, it was 29/1 in Biospeedy and Covirion (positivity 96.7%), 19/11 in the Qiagen kit (positivity 63.3%). When these samples were compared with the LAMP method it was found to be 19/11 (positivity 63.3%) on the first day and 18/12 (positivity 60%) on the fifth day. SARS-CoV-2 test studies will contribute to a proactive approach to the development of rapid diagnosis systems. The LAMP approach presents promising results to monitor exposed individuals and also improves screening efforts in potential ports of entry.

A Longitudinal Analysis of SARS-CoV-2 Antibody Responses Among People With HIV

Background

The concentration and duration of antibodies (Ab) to SARS-CoV-2 infection predicts the severity of the disease and the clinical outcomes. Older people and those with HIV have impaired immune responses, worse outcomes after SARS-CoV-2 infection, and lower antibody responses after viral infection and vaccination. This study evaluated an Ab response to SARS-CoV-2 in people with HIV (PWH) and without HIV (HIV-) and its association with age.

Methods

A total of 23 COVID+PWH and 21 COVID+HIV- participants were followed longitudinally for 6 months post-mild COVID-19. Immunoglobin G (IgG) and immunoglobin M (IgM) Ab responses were measured by an in-house developed ELISA. Time points and HIV status interaction were analyzed using Poisson generalized estimating equations, and correlations were analyzed using non-parametric tests.

Results

Median age in PWH was 55 years with 28.6% women, while in the HIV- group was 36 years with 60.9% women. The mean time from COVID-19 diagnosis to study enrollment was 16 days for PWH and 11 days for HIV-. The mean CD4+ T-cell count/μl for PWH was 772.10 (±365.21). SARS-CoV-2 IgM and IgG were detected at all time points and Ab response levels did not differ by HIV status (p > 0.05). At entry, age showed a weak direct association with IgG responses (ρ = 0.44, p < 0.05) in HIV- but did not show any association in PWH. Similar associations between age, IgG, and HIV status emerged at day 14 (T1; ρ = 0.50, p < 0.05), 3 months (T3; ρ = 0.50, p < 0.05), and 6 months visit (T4; ρ = 0.78, p < 0.05) in the HIV- group.

Conclusion

The Ab responses in the 6-month post-SARS-CoV-2 infection did not differ by HIV status, though a positive association was found between age and Ab response in older PWH. Results suggest that immune protection and vaccine responses are similar for PWH than for those without HIV infection.

Sensitively detecting antigen of SARS-CoV-2 by NIR-II fluorescent nanoparticles

Early detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is an efficient way to prevent the spread of coronavirus disease 2019 (COVID-19). Detecting SARS-CoV-2 antigen can be rapid and convenient, but it is still challenging to develop highly sensitive methods for effective diagnosis. Herein, a lateral flow assay (LFA) based on fluorescent nanoparticles emitting in the second near-infrared (NIR-II) window is developed for sensitive detection of SARS-CoV-2 antigen. Benefiting from the NIR-II fluorescence with high penetration and low autofluorescence, such NIR-II based LFA allows enhanced signal-to-background ratio, and the limit of detection is down to 0.01 ng·mL^-1 of SARS-CoV-2 antigen. In the clinical swab sample tests, the NIR-II LFA outperforms the colloidal gold LFA with higher overall percent agreement with the polymerase chain reaction test. The clinical samples with low antigen concentrations (∼ 0.015-∼ 0.068 ng·mL^-1) can be successfully detected by the NIR-II LFA, but fail for the colloidal gold LFA. The NIR-II LFA can provide a promising platform for highly sensitive, rapid, and cost-effective method for early diagnosis and mass screening of SARS-CoV-2 infection.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material (the operation procedure and cost of the materials needed of NIR-II lateral flow assays, the dynamic light scattering spectrum of the NIR-II nanoparticles, the components and testing principle, optimization of main parameters pertaining to the LFA performance, the colloidal gold LFA strip, the fluorescence intensity distribution curves and the T/C values of the strips for clinical samples by NIR-II LFA, and results of clinical swab samples detected by colloidal gold LFA) is available in the online version of this article at 10.1007/s12274-022-4351-1.

Detection of multiply charged protein ions using matrix-assisted laser desorption/ionization mass spectrometry and a force-dried droplet method with a 2-nitrophloroglucinol matrix

MALDI-MS of myoglobin using 2-NPG with HCl additive.

Recent advances in methods for the diagnosis of Corona Virus Disease 2019

Since the beginning of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) pandemic, it has been clear that effective methods for the diagnosis of Corona Virus Disease 2019 (COVID-19) are the key tools to control its epidemic. The current gold standard for diagnosing COVID-19 is the real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR), which is a sensitive and specific method to detect SARS-CoV-2. Other RNA-based methods include RNA sequencing (RNA-seq), droplet digital reverse transcription-polymerase chain reaction (ddRT-PCR), reverse transcription loop-mediated isothermal amplification (RT-LAMP), and clustered regularly interspaced short palindromic repeats (CRISPR). The serological testing of antibodies (IgM and IgG), nanoparticle-based lateral-flow assay, and enzyme-linked immunosorbent assay (ELISA) can be used to enhance the detection sensitivity and accuracy. Because antibodies are usually detected a week after the onset of symptoms, these tests are used to assess the overall infection rate in the community. Sine the fact that healthcare varies from country to country across the world, different types of diagnosing COVID-19 imaging technologies including chest computed tomography (CT), chest radiography, and lung ultrasound are used in different degrees. Besides, the pooling test is an important public health tool to reduce cost and increase testing capacity in low-risk area, while artificial intelligence (AI) may aid to increase the diagnostic efficiency of imaging-based methods. Finally, depending on the type of samples and stages of the disease, a combination of information on patient demographics and histories, clinical symptoms, results of molecular and serological diagnostic tests, and imaging information is highly recommended to achieve adequate diagnosis of patients with COVID-19.

Rapid testing for coronavirus disease 2019 (COVID-19)

Rapid testing, generally refers to the paper-based diagnostic platform known as "lateral flow assay" (LFA), has emerged as a critical asset to the containment of coronavirus disease 2019 (COVID-19) around the world. LFA technology stands out amongst peer platforms due to its cost-effective design, user-friendly interface, and low sample-to-readout times. This article aims to introduce its design, use, and practicality for the purpose of diagnosing SARS-CoV-2 infection. A connection is made from the normal COVID-19 immune response to the design and efficacy of rapid testing. Interference in test results is a challenge shared by most diagnostic platforms and can be rooted in various underlying issues. The current knowledge and situation about interference in rapid COVID-19 tests due to variant strains as well as vaccination are discussed. The cost and societal impact are reviewed as they play important roles in determining how to properly implement public testing practices. Perspectives on improving the performance, especially detection sensitivity, of LFA for COVID-19 are provided.

Evaluation of Anti-SARS-CoV-2 IgG Antibody in Healthcare Professionals Infected with COVID-19

Background: The knowledge of antibody’s significance and frequency in patients cured of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is extremely limited. Objectives: This study aimed to evaluate anti-SARS-CoV-2 IgG antibodies in patients exposed to SARS-CoV-2. Methods: Healthcare professionals infected with SARS-CoV-2 were enrolled in this study. The levels of anti-SARS-CoV-2 IgG antibodies were detected 15 days after the onset of symptoms and five months later. Results: A total of 167 patients with coronavirus disease 2019 (COVID-19) were evaluated, including 119 (71.3%) females and 48 (28.7%) males. Of the 88 polymerase chain reaction (PCR)-positive patients, 55 (62.5%) had IgG-positive antibodies, and of the 79 reverse transcriptase (RT)-PCR-negative patients, 12 (16.9%) had IgG-positive antibodies. Out of 23 anosmia cases, 19 (82.6%) had positive antibodies. There was a significant relationship between anosmia and positive antibody (P  =  0.001), but there was no correlation between antibody titers and gender and other disease symptoms. Immortally, 63 (94%) cases demonstrated high levels of anti-SARS-CoV-2 IgG antibodies after five months of infection. Moreover, 6.5% (N  =  11) of the total population were re-infected with COVID-19 six months later. Conclusions: Overall, anti-SARS-CoV-2 IgG antibodies detection may be an appropriate method to identify suspected patients with a negative RT-PCR test. Antibodies can remain high in most infected patients for up to five months after infection. Moreover, anosmia seems to be a valuable diagnostic factor, and the healthcare system should implement isolation measures for patients with anosmia.

Pulmonary Interstitial Matrix and Lung Fluid Balance From Normal to the Acutely Injured Lung

This review analyses the mechanisms by which lung fluid balance is strictly controlled in the air-blood barrier (ABB). Relatively large trans-endothelial and trans-epithelial Starling pressure gradients result in a minimal flow across the ABB thanks to low microvascular permeability aided by the macromolecular structure of the interstitial matrix. These edema safety factors are lost when the integrity of the interstitial matrix is damaged. The result is that small Starling pressure gradients, acting on a progressively expanding alveolar barrier with high permeability, generate a high transvascular flow that causes alveolar flooding in minutes. We modeled the trans-endothelial and trans-epithelial Starling pressure gradients under control conditions, as well as under increasing alveolar pressure (Palv) conditions of up to 25 cmH2O. We referred to the wet-to-dry weight (W/D) ratio, a specific index of lung water balance, to be correlated with the functional state of the interstitial structure. W/D averages ∼5 in control and might increase by up to ∼9 in severe edema, corresponding to ∼70% loss in the integrity of the native matrix. Factors buffering edemagenic conditions include: (i) an interstitial capacity for fluid accumulation located in the thick portion of ABB, (ii) the increase in interstitial pressure due to water binding by hyaluronan (the "safety factor" opposing the filtration gradient), and (iii) increased lymphatic flow. Inflammatory factors causing lung tissue damage include those of bacterial/viral and those of sterile nature. Production of reactive oxygen species (ROS) during hypoxia or hyperoxia, or excessive parenchymal stress/strain [lung overdistension caused by patient self-induced lung injury (P-SILI)] can all cause excessive inflammation. We discuss the heterogeneity of intrapulmonary distribution of W/D ratios. A W/D ∼6.5 has been identified as being critical for the transition to severe edema formation. Increasing Palv for W/D > 6.5, both trans-endothelial and trans-epithelial gradients favor filtration leading to alveolar flooding. Neither CT scan nor ultrasound can identify this initial level of lung fluid balance perturbation. A suggestion is put forward to identify a non-invasive tool to detect the earliest stages of perturbation of lung fluid balance before the condition becomes life-threatening.

Single-Cell Immunogenomic Approach Identified SARS-CoV-2 Protective Immune Signatures in Asymptomatic Direct Contacts of COVID-19 Cases

The response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is largely impacted by the level of virus exposure and status of the host immunity. The nature of protection shown by direct asymptomatic contacts of coronavirus disease 2019 (COVID-19)-positive patients is quite intriguing. In this study, we have characterized the antibody titer, SARS-CoV-2 surrogate virus neutralization, cytokine levels, single-cell T-cell receptor (TCR), and B-cell receptor (BCR) profiling in asymptomatic direct contacts, infected cases, and controls. We observed significant increase in antibodies with neutralizing amplitude in asymptomatic contacts along with cytokines such as Eotaxin, granulocyte-colony stimulating factor (G-CSF), interleukin 7 (IL-7), migration inhibitory factor (MIF), and macrophage inflammatory protein-1α (MIP-1α). Upon single-cell RNA (scRNA) sequencing, we explored the dynamics of the adaptive immune response in few representative asymptomatic close contacts and COVID-19-infected patients. We reported direct asymptomatic contacts to have decreased CD4⁺ naive T cells with concomitant increase in CD4⁺ memory and CD8⁺ Temra cells along with expanded clonotypes compared to infected patients. Noticeable proportions of class switched memory B cells were also observed in them. Overall, these findings gave an insight into the nature of protection in asymptomatic contacts.

A novel G-quadruplex aptamer-based spike trimeric antigen test for the detection of SARS-CoV-2

The recent SARS-CoV-2 outbreak has been declared a global health emergency. It will take years to vaccinate the whole population to protect them from this deadly virus, hence the management of SARS-CoV-2 largely depends on the widespread availability of an accurate diagnostic test. Toward addressing the unmet need of a reliable diagnostic test in the current work by utilizing the power of Systematic Evolution of Ligands by EXponential enrichment, a 44-mer G-quadruplex-forming DNA aptamer against spike trimer antigen of SARS-CoV-2 was identified. The lead aptamer candidate (S14) was characterized thoroughly for its binding, selectivity, affinity, structure, and batch-to-batch variability by utilizing various biochemical, biophysical, and in silico techniques. S14 has demonstrated a low nanomolar KD, confirming its tight binding to a spike antigen of SARS-CoV-2. S14 can detect as low as 2 nM of antigen. The clinical evaluation of S14 aptamer on nasopharyngeal swab specimens (n = 232) has displayed a highly discriminatory response between SARS-CoV-2 infected individuals from the non-infected one with a sensitivity and specificity of ∼91% and 98%, respectively. Importantly, S14 aptamer-based test has evinced a comparable performance with that of RT-PCR-based assay. Altogether, this study established the utility of aptamer technology for the detection of SARS-CoV-2.

In-silico design of a multi-epitope for developing sero-diagnosis detection of SARS-CoV-2 using spike glycoprotein and nucleocapsid antigens

COVID-19 is a pandemic disease caused by novel corona virus, SARS-CoV-2, initially originated from China. In response to this serious life-threatening disease, designing and developing more accurate and sensitive tests are crucial. The aim of this study is designing a multi-epitope of spike and nucleocapsid antigens of COVID-19 virus by bioinformatics methods. The sequences of nucleotides obtained from the NCBI Nucleotide Database. Transmembrane structures of proteins were predicted by TMHMM Server and the prediction of signal peptide of proteins was performed by Signal P Server. B-cell epitopes' prediction was performed by the online prediction server of IEDB server. Beta turn structure of linear epitopes was also performed using the IEDB server. Conformational epitope prediction was performed using the CBTOPE and eventually, eight antigenic epitopes with high physicochemical properties were selected, and then, all eight epitopes were blasted using the NCBI website. The analyses revealed that α-helices, extended strands, β-turns, and random coils were 28.59%, 23.25%, 3.38%, and 44.78% for S protein, 21.24%, 16.71%, 6.92%, and 55.13% for N Protein, respectively. The S and N protein three-dimensional structure was predicted using the prediction I-TASSER server. In the current study, bioinformatics tools were used to design a multi-epitope peptide based on the type of antigen and its physiochemical properties and SVM method (Machine Learning) to design multi-epitopes that have a high avidity against SARS-CoV-2 antibodies to detect infections by COVID-19.

Diagnosing COVID-19 in human sera with detected immunoglobulins IgM and IgG by means of Raman spectroscopy

The severe COVID-19 pandemic requires the development of novel, rapid, accurate, and label-free techniques that facilitate the detection and discrimination of SARS-CoV-2 infected subjects. Raman spectroscopy has been used to diagnose COVID-19 in serum samples of suspected patients without clinical symptoms of COVID-19 but presented positive immunoglobulins M and G (IgM and IgG) assays versus Control (negative IgM and IgG). A dispersive Raman spectrometer (830 nm, 350 mW) was employed, and triplicate spectra were obtained. A total of 278 spectra were used from 94 serum samples (54 Control and 40 COVID-19). The main spectral differences between the positive IgM and IgG versus Control, evaluated by principal component analysis (PCA), were features assigned to proteins including albumin (lower in the group COVID-19 and in the group IgM/IgG and IgG positive) and features assigned to lipids, phospholipids, and carotenoids (higher the group COVID-19 and in the group IgM/IgG positive). Features referred to nucleic acids, tryptophan, and immunoglobulins were also seen (higher the group COVID-19). A discriminant model based on partial least squares regression (PLS-DA) found sensitivity of 84.0%, specificity of 95.0%, and accuracy of 90.3% for discriminating positive Ig groups versus Control. When considering individual Ig group versus Control, it was found sensitivity of 77.3%, specificity of 97.5%, and accuracy of 88.8%. The higher classification error was found for the IgM group (no success classification). Raman spectroscopy may become a technique of choice for rapid serological evaluation aiming COVID-19 diagnosis, mainly detecting the presence of IgM/IgG and IgG after COVID-19 infection.

Point-of-care COVID-19 diagnostics powered by lateral flow assay

Since its first discovery in December 2019, the global coronavirus disease 2019 (COVID-19) pandemic caused by the novel coronavirus (SARS-CoV-2) has been posing a serious threat to human life and health. Diagnostic testing is critical for the control and management of the COVID-19 pandemic. In particular, diagnostic testing at the point of care (POC) has been widely accepted as part of the post restriction COVID-19 control strategy. Lateral flow assay (LFA) is a popular POC diagnostic platform that plays an important role in controlling the COVID-19 pandemic in industrialized countries and resource-limited settings. Numerous pioneering studies on the design and development of diverse LFA-based diagnostic technologies for the rapid diagnosis of COVID-19 have been done and reported by researchers. Hundreds of LFA-based diagnostic prototypes have sprung up, some of which have been developed into commercial test kits for the rapid diagnosis of COVID-19. In this review, we summarize the crucial role of rapid diagnostic tests using LFA in targeting SARS-CoV-2-specific RNA, antibodies, antigens, and whole virus. Then, we discuss the design principle and working mechanisms of these available LFA methods, emphasizing their clinical diagnostic efficiency. Ultimately, we elaborate the challenges of current LFA diagnostics for COVID-19 and highlight the need for continuous improvement in rapid diagnostic tests.

Undetectable SARS-CoV-2 active adaptive immunity-post-vaccination or post-COVID-19 severe disease-after immunosuppressants use

Since the beginning of COVID-19 vaccination in New Jersey in December 2020, we have observed multiple cases of undetectable adaptive immunity, post-vaccination or post-COVID-19 infection, in patients using immunosuppressants. Here, we present three cases of patients using immunosuppressants: mycophenolate and tacrolimus for renal transplant; ocrelizumab for multiple sclerosis and rituximab for peripheral ulcerative keratitis. All three patients were admitted for acute respiratory distress syndrome (ARDS) from COVID-19 pneumonia; two patients reported having received full COVID-19 vaccination prior to admission and one unvaccinated patient required readmission. Our findings showed that these patients tested negative for SARS-CoV-2 IgM spike and CoV-2 IgG nucleocapsid antibodies. All three patients were treated with standard-of-care remdesivir, dexamethasone and convalescent plasma; two recovered successfully and one patient died from respiratory failure secondary to worsening ARDS from COVID-19 pneumonia. We highlight the challenges of treating immunosuppressed patients with COVID-19 pneumonia, in an era where dissemination of such information is paramount to helping doctors standardise and improve the quality of care for these patients.

SARS-CoV-2 Seroprevalence and Profiles Among Convalescents in Sichuan Province, China

Objectives: To explore and understand the SARS-CoV-2 seroprevalence of convalescents, the association between antibody levels and demographic factors, and the seroepidemiology of convalescents of COVID-19 till March 2021.

Methods: We recruited 517 voluntary COVID-19 convalescents in Sichuan Province and collected 1,707 serum samples till March 2021. Then we reported the seroprevalence and analyzed the associated factors.

Results: Recent travel history was associated with IgM levels. Convalescents who had recent travel history were less likely to be IgM antibody negative [OR = 0.232, 95% CI: (0.128, 0.420)]. Asymptomatic cases had, approximately, twice the odds of being IgM antibody negative compared with symptomatic cases [OR = 2.583, 95% CI: (1.554, 4.293)]. Participants without symptoms were less likely to be IgG seronegative than those with symptoms [OR = 0.511, 95% CI: (0.293, 0.891)]. Convalescents aged 40–59 were less likely to be IgG seronegative than those aged below 20 [OR = 0.364, 95% CI: (0.138, 0.959)]. The duration of positive IgM antibodies persisted 365 days while the IgG persisted more than 399 days.

Conclusions: Our findings suggested that recent travel history might be associated with the antibody levels of IgM, while age could be associated with the antibody levels of IgG. Infection type could be associated with both antibody levels of IgM and IgG that declined quicker in asymptomatic cases.

An outlook on coronavirus disease 2019 detection methods

Diagnostic testing plays a fundamental role in the mitigation and containment of coronavirus disease 2019 (COVID-19), as it enables immediate quarantine of those who are infected and contagious and is essential for the epidemiological characterization of the virus and estimating the number of infected cases worldwide. Confirmation of viral infections, such as COVID-19, can be achieved through two general approaches: nucleic acid amplification tests (NAATs) or molecular tests, and serological or antibody-based tests. The genetic material of the pathogen is detected in NAAT, and in serological tests, host antibodies produced in response to the pathogen are identified. Other methods of diagnosing COVID-19 include radiological imaging of the lungs and in vitro detection of viral antigens. This review covers different approaches available to diagnosing COVID-19 by outlining their advantages and shortcomings, as well as appropriate indications for more accurate testing.

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Diagnostic tests to detect coronavirus disease 2019 (COVID-19).

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Advantages and disadvantages associated with each detection method.

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Implications for a more accurate and rapid testing of COVID-19 or other similar future emergent viruses.

Human IgM and IgG Responses to an Inactivated SARS-CoV-2 Vaccine

Objective

The ongoing COVID-19 pandemic warrants accelerated efforts to test vaccine candidates. To explore the influencing factors on vaccine-induced effects, antibody responses to an inactivated SARS-CoV-2 vaccine in healthy individuals who were not previously infected by COVID-19 were assessed.

Methods

All subjects aged 18–60 years who did not have SARS-CoV-2 infection at the time of screening from June 19, 2021, to July 02, 2021, were approached for inclusion. All participants received two doses of inactivated SARS-CoV-2 vaccine. Serum IgM and IgG antibodies were detected using a commercial kit after the second dose of vaccination. A positive result was defined as 10 AU/mL or more and a negative result as less than 10 AU/mL. This retrospective study included 97 infection-naïve individuals (mean age 35.6 years; 37.1% male, 62.9% female).

Results

The seropositive rates of IgM and IgG antibody responses elicited after the second dose of inactivated SARS-CoV-2 vaccine were 3.1% and 74.2%, respectively. IgG antibody levels were significantly higher than IgM levels (P<0.0001). Sex had no effect on IgM and IgG antibody response after the second dose. The mean anti-IgG level in older persons (⩾42 years) was significantly lower than that of younger recipients. There was a significantly lower antibody level at > 42 days compared to that at 0–20 days (P<0.05) and 21–31 days (P<0.05) after the second dose.

Conclusion

IgG antibody response could be induced by inactivated SARS-CoV-2 vaccine in healthy individuals (>18 years), which can be influenced by age and detection time after the second dose of vaccination.

Feasibility of Rapid Diagnostic Technology for SARS-CoV-2 Virus Using a Trace Amount of Saliva

Containment of SARS-CoV-2 has become an urgent global issue. To overcome the problems of conventional quantitative polymerase chain reaction (qPCR) tests, we verified the usefulness of a mobile qPCR device that utilizes mouthwash to obtain a saliva sample with the aim of developing a rapid diagnostic method for SARS-CoV-2. First, we examined whether anyone could easily operate this device. Then, we examined whether RNA in the mouthwash could be detected in a short time. In addition, we investigated whether it was possible to diagnose SARS-CoV-2 infection using mouthwash obtained from COVID-19 patients undergoing hospitalization. The results revealed that all subjects were able to complete the operation properly without error. In addition, RNase P was detected in the mouthwash without pretreatment. The average detection time was 18 min, which is significantly shorter than conventional qPCR devices. Furthermore, this device detected SARS-CoV-2 in the mouthwash of a COVID-19 patient undergoing hospitalization. The above findings verified the efficacy of this diagnostic method, which had a low risk of infection, was technically simple, and provided stable results. Therefore, this method is useful for the rapid detection of SARS-CoV-2.

Electrochemical Biosensor with Enhanced Antifouling Capability Based on Amyloid-like Bovine Serum Albumin and a Conducting Polymer for Ultrasensitive Detection of Proteins in Human Serum

Biofouling has been a substantial burden on biomarker analysis in complex biological media, leading to poor sensitivity and selectivity or even malfunction of the sensing devices. In this work, an electrochemical biosensor with excellent antifouling ability and high stability was fabricated based on amyloid-like bovine serum albumin (AL-BSA) crosslinked with the conducting polymer polyaniline (PANI). Compared with the crosslinked conventional bovine serum albumin (BSA), the crosslinked AL-BSA exhibited enhanced antifouling capability, and it was able to form an effective antifouling film within a significantly short reaction time. With further immobilization of immunoglobulin M (IgM) antibodies onto the prepared AL-BSA surface via the formation of amide bonds, an electrochemical biosensor capable of assaying IgM in human serum samples with superior selectivity and sensitivity was constructed. The biosensor exhibited excellent antifouling performance even in 100% human serum, a low limit of detection down to 2.32 pg mL^-1, and acceptable accuracy for real sample analysis compared with the standard enzyme-linked immunosorbent assay for IgM detection. This strategy of using AL-BSA to construct antifouling sensing interfaces provided a reliable diagnostic method for the detection of a series of protein biomarkers in complex biological media.

Pre-evaluation assessment of serological-based COVID-19 point-of-care lateral flow assays in Kenya

Background

Timely testing is a key determinant of management outcomes of coronavirus disease 2019 (COVID-19). Real-time reverse transcription polymerase chain reaction tests are currently the mainstay for COVID-19 testing. However, serological point-of-care tests (PoCTs) can be useful in identifying asymptomatic and recovered cases, as well as herd immunity.

Objective

The aim of this study was to assess COVID-19 PoCTs in Kenya to support the emergency use authorisation of these tests.

Methods

Between March 2020 and May 2020, 18 firms, of which 13 were from China, submitted their PoCTs to the national regulatory authority, the Pharmacy and Poison Board, who in turn forwarded them to the Kenya Medical Research Institute for pre-evaluation assessment. The tests were run with real-time reverse transcription polymerase chain reaction COVID-19-positive samples. Pre-COVID-19 plasma samples that were collected in June 2019 were used as negative samples. The shelf lives of the PoCTs ranged from 6 to 24 months.

Results

Only nine (50%) tests had sensitivities ≥ 40% (range: 40% - 60%) and the ability of these tests to detect IgM ranged from 0% to 50%. Many (7/18; 38.9%) of the kits had very weak IgM and IgG band intensities (range: 2-3).

Conclusion

Serological-based PoCTs available in Kenya can only detect COVID-19 in up to 60% of the infected population.

SARS-CoV-2 antibodies in employees working in non-medical contact-intensive professions in the Netherlands: Baseline data from the prospective COco-study

COVID-19 has made a global impact since early 2020, requiring characterization of the SARS-CoV-2 virus, including transmission risk. The COco-study aims to evaluate the risk for COVID-19 infections in two non-medical contact-intensive professions. COco is a prospective cohort study evaluating SARS-CoV-2 antibodies in hairdressers and hospitality personnel in the province of North-Brabant in the Netherlands, using a total antibody enzyme-linked immunosorbent assay. Baseline data from June/July 2020 were analyzed. Participants filled out a questionnaire, providing information on demographics, health, work situation, and risk factors for COVID-19. Odds ratios (OR) and 95% confidence intervals (95% CI) were calculated using logistic regression. In June/July 2020, 497 participants were enrolled: 236 hairdressers, 259 hospitality employees, and two participants worked in both industries. Hospitality staff was more frequently seropositive than hairdressers (14.2% versus 8.0%, respectively; OR 1.9, 95% CI 1.1-3.4). Furthermore, a high education level (OR 3.0, 95% CI: 1.7-5.6) and increased alcohol use (OR, 7 glasses per week increment: 1.3, 95% CI: 1.1-1.5) were associated with seropositivity. Of the 56 seropositive participants, 18 (32%) had not experienced any COVID-19 symptoms. The symptoms anosmia/ageusia differed most evidently between seropositive and seronegative participants (53.6% versus 5.7%, respectively; P < 0.001 (chi-squared test)). In conclusion, four months after the first identified COVID-19 patient in the Netherlands, employees in the hospitality industry had significantly more frequently detectable SARS-CoV-2 antibodies than hairdressers.

People living with HIV easily lose their immune response to SARS-CoV-2: result from a cohort of COVID-19 cases in Wuhan, China

BACKGROUND

To date, whether the immune response for SARS-CoV-2 infection among people living with HIV(PLWH) is different from HIV-naïve individuals is still not clear.

METHODS

In this cohort study, COVID-19 patients admitted to hospitals in Wuhan between January 15 and April 1, 2020, were enrolled. Patients were categorized into PLWH and HIV-naïve group. All patients were followed up regularly (every 15 days) until November 30, 2020, and the immune response towards SARS-CoV-2 was observed.

RESULTS

Totally, 18 PLWH and 185 HIV-naïve individuals with COVID-19 were enrolled. The positive conversion rates of IgG were 56% in PLWH and 88% in HIV-naïve patients respectively, and the peak was on the 45th day after COVID-19 onset. However, the positive rate of IgG dropped to 12% in PLWH and 33% among HIV-naïve individuals by the end of the study. The positive conversion rate of IgG among asymptomatic carriers is significantly lower than that among patients with moderate disease (AOR = 0.24, 95% CI 0.07-0.85). PLWH had a lower IgG seroconversion rate (AOR = 0.11, 95% CI 0.03-0.39) and shorter IgG duration (AHR = 3.99, 95% CI 1.43-11.13) compared to HIV-naïve individuals. Patients with higher lymphocyte counts at onset had a lower positive conversion rate (AOR = 0.30, 95% CI 0.10-0.87) and shorter duration for IgG (AHR = 4.01, 95% CI 1.78-9.02).

CONCLUSIONS

The positive conversion rate of IgG for SARS-CoV-2 was relatively lower and quickly lost in PLWH.

COVID-19 Testing and Diagnostics: A Review of Commercialized Technologies for Cost, Convenience and Quality of Tests

Population-scale and rapid testing for SARS-CoV-2 continues to be a priority for several parts of the world. We revisit the in vitro technology platforms for COVID-19 testing and diagnostics-molecular tests and rapid antigen tests, serology or antibody tests, and tests for the management of COVID-19 patients. Within each category of tests, we review the commercialized testing platforms, their analyzing systems, specimen collection protocols, testing methodologies, supply chain logistics, and related attributes. Our discussion is essentially focused on test products that have been granted emergency use authorization by the FDA to detect and diagnose COVID-19 infections. Different strategies for scaled-up and faster screening are covered here, such as pooled testing, screening programs, and surveillance testing. The near-term challenges lie in detecting subtle infectivity profiles, mapping the transmission dynamics of new variants, lowering the cost for testing, training a large healthcare workforce, and providing test kits for the masses. Through this review, we try to understand the feasibility of universal access to COVID-19 testing and diagnostics in the near future while being cognizant of the implicit tradeoffs during the development and distribution cycles of new testing platforms.

Application of Nanomaterials as an Advanced Strategy for the Diagnosis, Prevention, and Treatment of Viral Diseases

The coronavirus disease (COVID-19) pandemic poses serious global health concerns with the continued emergence of new variants. The periodic outbreak of novel emerging and re-emerging infectious pathogens has elevated concerns and challenges for the future. To develop mitigation strategies against infectious diseases, nano-based approaches are being increasingly applied in diagnostic systems, prophylactic vaccines, and therapeutics. This review presents the properties of various nanoplatforms and discusses their role in the development of sensors, vectors, delivery agents, intrinsic immunostimulants, and viral inhibitors. Advanced nanomedical applications for infectious diseases have been highlighted. Moreover, physicochemical properties that confer physiological advantages and contribute to the control and inhibition of infectious diseases have been discussed. Safety concerns limit the commercial production and clinical use of these technologies in humans; however, overcoming these limitations may enable the use of nanomaterials to resolve current infection control issues via application of nanomaterials as a platform for the diagnosis, prevention, and treatment of viral diseases.

Immunological assessment of SARS-CoV-2 infection in pregnancy from diagnosis to delivery: A multicentre prospective study

BACKGROUND

Background Population-based data on SARS-CoV-2 infection in pregnancy and assessment of passive immunity to the neonate, is lacking. We profiled the maternal and fetal response using a combination of viral RNA from naso-pharyngeal swabs and serological assessment of antibodies against SARS-CoV-2.

METHODS

This multicentre prospective observational study was conducted between March 24th and August 31st 2020. Two independent cohorts were established, a symptomatic SARS-CoV-2 cohort and a cohort of asymptomatic pregnant women attending two of the largest maternity hospitals in Europe. Symptomatic women were invited to provide a serum sample to assess antibody responses. Asymptomatic pregnant women provided a nasopharyngeal swab and serum sample. RT-PCR for viral RNA was performed using the Cobas SARS-CoV-2 6800 platform (Roche). Umbilical cord bloods were obtained at delivery. Maternal and fetal serological response was measured using both the Elecsys® Anti-SARS-CoV-2 immunoassay (Roche), Abbott SARS-CoV-2 IgG Assay and the IgM Architect assay. Informed written consent was obtained from all participants.

RESULTS

Ten of twenty three symptomatic women had SARS-CoV-2 RNA detected on nasopharyngeal swabs. Five (5/23, 21.7%) demonstrated serological evidence of anti-SARS-CoV-2 IgG antibodies and seven (30.4%, 7/23) were positive for IgM antibodies. In the asymptomatic cohort, the prevalence of SARS-CoV-2 infection in RNA was 0.16% (1/608). IgG SARS-CoV-2 antibodies were detected in 1·67% (10/598, 95% CI 0·8%-3·1%) and IgM in 3·51% (21/598, 95% CI 2·3-5·5%). Nine women had repeat testing post the baseline test. Four (4/9, 44%) remained IgM positive and one remained IgG positive. 3 IgG anti-SARS-CoV-2 antibodies were detectable in cord bloods from babies born to five seropositive women who delivered during the study. The mean gestation at serological test was 34 weeks. The mean time between maternal serologic positivity and detection in umbilical cord samples was 28 days.

CONCLUSION

Using two independent serological assays, we present a comprehensive illustration of the antibody response to SARS-CoV-2 in pregnancy, and show a low prevalence of asymptomatic SARS-CoV2. Transplacental migration of anti-SARS-CoV-2 antibodies was identified in cord blood of women who demonstrated antenatal anti-SARS-CoV-2 antibodies, raising the possibility of passive immunity.

[Herd immunity to SARS-CoV-2 in the Novosibirsk Region population amid the COVID-19 pandemic]

AIM

To determine the level of SARS-CoV-2 seroprevalence among the Novosibirsk Region population against the background of the COVID-19 pandemic.

MATERIAL AND METHODS

The work was carried out in 2 phases: 1) a cross-sectional cohort study performed 28.06- 15.07.2020; 2) longitudinal cohort 3-stage seromonitoring: 1st stage 28.06-15.07.2020; 2nd 14.09-04.10.2020; 3rd 10-30.12.2020 The work was carried out according to a unified methodology developed by Rospotrebnadzor with the participation of St-Petersburg Pasteur Institute, taking into account the recommendations of the WHO. IgG antibodies to the SARS-CoV-2 nucleocapsid protein were detected by ELISA using a kit of reagents produced by the SRCMSB (Obolensk) according to the manufacturer's instructions. Statistical analysis was performed using Microsoft Excel 2010 and other programs.

RESULTS

The seroprevalence in the region's population was 9.1% (95% CI 8.0-10.2): maximum in children 14-17 years old (17.6%, 95% CI 12.3-23.9) and persons over 75 years (14.8%, 95% CI 11.4-18.8), minimum among persons 30-39 years old (4.9%, 95% CI 3.0-8.0). Increased rate was noted among the unemployed (15.4%, 95% CI 9.9-17.1) and other individuals (13.0%, 95% CI 8.6-18.5). Seroprevalence was 33.3% (95% CI 16.3-59.0) in COVID-19 convalescents and 19.0% (95% CI 13.9-25.0) in contact persons. More than 94.7% (95% CI 91.2-97.2) of seropositive individuals were asymptomatic. During the serological monitoring, seroprevalence increased from 7.4% (95% CI 6.2-8.9) at 1st stage 1 to 12.4% (95% CI 10.6-14.3) at 2nd , and 31% (95% CI 28.8-33.3) at 3rd stage.

CONCLUSION

SARS-CoV-2 herd immunity has not reached the threshold level, this does not exclude exacerbation of the epidemic process.

Immunologic memory to SARS-CoV-2 in convalescent COVID-19 patients at 1 year postinfection

Background

Understanding the complexities of immune memory to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is key to gain insights into the durability of protective immunity against reinfection.

Objective

We sought to evaluate the immune memory to SARS-CoV-2 in convalescent patients with longer follow-up time.

Methods

SARS-CoV-2–specific humoral and cellular responses were assessed in convalescent patients with coronavirus disease 2019 (COVID-19) at 1 year postinfection.

Results

A total of 78 convalescent patients with COVID-19 (26 moderate, 43 severe, and 9 critical) were recruited after 1 year of recovery. The positive rates of both anti–receptor-binding domain and antinucleocapsid antibodies were 100%, whereas we did not observe a statistical difference in antibody levels among different severity groups. Accordingly, the prevalence of neutralizing antibodies (nAbs) reached 93.59% in convalescent patients. Although nAb titers displayed an increasing trend in convalescent patients with increased severity, the difference failed to achieve statistical significance. Notably, there was a significant correlation between nAb titers and anti–receptor-binding domain levels. Interestingly, SARS-CoV-2–specific T cells could be robustly maintained in convalescent patients, and their number was positively correlated with both nAb titers and anti–receptor-binding domain levels. Amplified SARS-CoV-2–specific CD4⁺ T cells mainly produced a single cytokine, accompanying with increased expression of exhaustion markers including PD-1, Tim-3, TIGIT, CTLA-4, and CD39, while the proportion of multifunctional cells was low.

Conclusions

Robust SARS-CoV-2–specific humoral and cellular responses are maintained in convalescent patients with COVID-19 at 1 year postinfection. However, the dysfunction of SARS-CoV-2–specific CD4⁺ T cells supports the notion that vaccination is needed in convalescent patients for preventing reinfection.

Risk factors for SARS-CoV-2 seroprevalence following the first pandemic wave in UK healthcare workers in a large NHS Foundation Trust

Background: We aimed to measure SARS-CoV-2 seroprevalence in a cohort of healthcare workers (HCWs) during the first UK wave of the COVID-19 pandemic, explore risk factors associated with infection, and investigate the impact of antibody titres on assay sensitivity. Methods: HCWs at Sheffield Teaching Hospitals NHS Foundation Trust were prospectively enrolled and sampled at two time points. SARS-CoV-2 antibodies were tested using an in-house assay for IgG and IgA reactivity against Spike and Nucleoprotein (sensitivity 99·47%, specificity 99·56%). Data were analysed using three statistical models: a seroprevalence model, an antibody kinetics model, and a heterogeneous sensitivity model. Results: As of 12th June 2020, 24·4% (n=311/1275) of HCWs were seropositive. Of these, 39·2% (n=122/311) were asymptomatic. The highest adjusted seroprevalence was measured in HCWs on the Acute Medical Unit (41·1%, 95% CrI 30·0-52·9) and in Physiotherapists and Occupational Therapists (39·2%, 95% CrI 24·4-56·5). Older age groups showed overall higher median antibody titres. Further modelling suggests that, for a serological assay with an overall sensitivity of 80%, antibody titres may be markedly affected by differences in age, with sensitivity estimates of 89% in those over 60 years but 61% in those ≤30 years. Conclusions:  HCWs in acute medical units working closely with COVID-19 patients were at highest risk of infection, though whether these are infections acquired from patients or other staff is unknown. Current serological assays may underestimate seroprevalence in younger age groups if validated using sera from older and/or more symptomatic individuals.

Olfactory dysfunction in SARS-CoV-2 infection: Focus on odorant specificity and chronic persistence

BACKGROUND

Smell dysfunction has been recognized as an early symptom of SARS-CoV-2 infection, often occurring before the onset of core symptoms of the respiratory tract, fever or muscle pain. In most cases, olfactory dysfunction is accompanied by reduced sense of taste, is partial (microsmia) and seems to normalize after several weeks, however, especially in cases of virus-induced complete smell loss (anosmia), there are indications of persisting deficits even 2 months after recovery from the acute disease, pointing towards the possibility of chronic or even permanent smell reduction for a significant part of the patient population. To date, we have no knowledge on the specificity of anosmia towards specific odorants or chemicals and about the longer-term timeline of its persistence or reversal.

METHODS

In this longitudinal study, 70 participants from a community in Lower Austria that had been tested positive for either IgG or IgM SARS-CoV-2 titers in June 2020 and a healthy control cohort (N = 348) underwent smell testing with a 12-item Cross-Cultural Smell Identification Test (CC-SIT), based upon items from the University of Pennsylvania Smell Identification Test (UPSIT). The test was performed in October 2020, i.e. 4 months after initial diagnosis via antibody testing. Results were analyzed using statistical tests for contingency for each smell individually in order to detect whether reacquisition of smell is dependent on specific odorant types.

RESULTS

For all odorants tested, except the odor "smoke", even 4 months or more after acute SARS-CoV-2 infection, participants with a positive antibody titer had a reduced sense of smell when compared to the control group. On average, while the control cohort detected a set of 12 different smells with 88.0% accuracy, the antibody-positive group detected 80.0% of tested odorants. A reduction of accuracy of detection by 9.1% in the antibody-positive cohort was detected. Recovery of the ability to smell was particularly delayed for three odorants: strawberry (encoded by the aldehyde ethylmethylphenylglycidate), lemon (encoded by citronellal, a monoterpenoid aldehyde), and soap (alkali metal salts of the fatty acids plus odorous additives) exhibit a sensitivity of detection of an infection with SARS-CoV-2 of 31.0%, 41.0% and 40.0%, respectively.

CONCLUSION

Four months or more after acute infection, smell performance of SARS-CoV-2 positive patients with mild or no symptoms is not fully recovered, whereby the ability to detect certain odors (strawberry, lemon and soap) is particularly affected, suggesting the possibility that these sensitivity to these smells may not only be lagging behind but may be more permanently affected.

Development of a high-sensitivity ELISA detecting IgG, IgA and IgM antibodies to the SARS-CoV-2 spike glycoprotein in serum and saliva

Detecting antibody responses during and after SARS-CoV-2 infection is essential in determining the seroepidemiology of the virus and the potential role of antibody in disease. Scalable, sensitive and specific serological assays are essential to this process. The detection of antibody in hospitalized patients with severe disease has proven relatively straightforward; detecting responses in subjects with mild disease and asymptomatic infections has proven less reliable. We hypothesized that the suboptimal sensitivity of antibody assays and the compartmentalization of the antibody response may contribute to this effect. We systematically developed an ELISA, optimizing different antigens and amplification steps, in serum and saliva from non-hospitalized SARS-CoV-2-infected subjects. Using trimeric spike glycoprotein, rather than nucleocapsid, enabled detection of responses in individuals with low antibody responses. IgG1 and IgG3 predominate to both antigens, but more anti-spike IgG1 than IgG3 was detectable. All antigens were effective for detecting responses in hospitalized patients. Anti-spike IgG, IgA and IgM antibody responses were readily detectable in saliva from a minority of RT-PCR confirmed, non-hospitalized symptomatic individuals, and these were mostly subjects who had the highest levels of anti-spike serum antibodies. Therefore, detecting antibody responses in both saliva and serum can contribute to determining virus exposure and understanding immune responses after SARS-CoV-2 infection.

Dynamic Antibody Responses in Patients with Different Severity of COVID-19: A Retrospective Study

INTRODUCTION

The coronavirus disease 2019 (COVID-19) pandemic is a serious public health event and poses a global health threat. To study the specific antibody responses would contribute to a better understanding of COVID-19.

METHODS

We collected complete follow-up data from 777 patients with pathogen-confirmed COVID-19 with corresponding immunoglobulin G and M (IgG/IgM) testing results.

RESULTS

Overall, the positive rates of IgG and IgM in severe patients were slightly higher than those in non-severe patients. In addition, higher IgG levels were detected in severe patients compared to non-severe patients (P = 0.026). Through further analysis, differences in IgG were only significant in serum samples taken in the first 14 days of disease onset (P < 0.001). On the basis of analysis of antibody expression levels at different time points in 74 patients who had undergone more than three detection tests, we found that the differences in IgG levels between the severe/non-severe patients were more pronounced than those of IgM. On multivariate logistic regression, after adjusting for cofactors, the higher anti-SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) IgG levels observed in the first 14 days of disease onset were independently associated with severe COVID-19 disease (odds ratio (OR) = 1.368, 95% confidence interval (CI) 1.138-1.645).

CONCLUSION

We observed differences in antibody responses among patients with different severity of COVID-19. A high IgG level in the first 14 days of disease may be positively associated with disease severity.

Applications of laboratory findings in the prevention, diagnosis, treatment, and monitoring of COVID-19

The worldwide pandemic of coronavirus disease 2019 (COVID-19) presents us with a serious public health crisis. To combat the virus and slow its spread, wider testing is essential. There is a need for more sensitive, specific, and convenient detection methods of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Advanced detection can greatly improve the ability and accuracy of the clinical diagnosis of COVID-19, which is conducive to the early suitable treatment and supports precise prophylaxis. In this article, we combine and present the latest laboratory diagnostic technologies and methods for SARS-CoV-2 to identify the technical characteristics, considerations, biosafety requirements, common problems with testing and interpretation of results, and coping strategies of commonly used testing methods. We highlight the gaps in current diagnostic capacity and propose potential solutions to provide cutting-edge technical support to achieve a more precise diagnosis, treatment, and prevention of COVID-19 and to overcome the difficulties with the normalization of epidemic prevention and control.

SARS-CoV-2 Seroprevalence Structure of the Russian Population during the COVID-19 Pandemic

The SARS-CoV-2 pandemic, which came to Russia in March 2020, is accompanied by morbidity level changes and can be tracked using serological monitoring of a representative population sample from Federal Districts (FDs) and individual regions. In a longitudinal cohort study conducted in 26 model regions of Russia, distributed across all FDs, we investigated the distribution and cumulative proportions of individuals with antibodies (Abs) to the SARS-CoV-2 nucleocapsid antigen (Ag), in the period from June to December 2020, using a three-phase monitoring process. In addition, during the formation of the cohort of volunteers, the number of seropositive convalescents, persons who had contact with patients or COVID-19 convalescents, and the prevalence of asymptomatic forms of infection among seropositive volunteers were determined. According to a uniform methodology, 3 mL of blood was taken from the examined individuals, and plasma was separated, from which the presence of Abs to nucleocapsid Ag was determined on a Thermo Scientific Multiascan FC device using the "ELISA anti-SARS-CoV-2 IgG" reagent set (prod. Scientific Center for Applied Microbiology and Biotechnology), in accordance with the developer's instructions. Volunteers (74,158) were surveyed and divided into seven age groups (1-17, 18-29, 30-39, 40-49, 59-59, 60-69, and 70+ years old), among whom 14,275 were identified as having antibodies to SARS-CoV-2. The average percent seropositive in Russia was 17.8% (IQR: 8.8-23.2). The largest proportion was found among children under 17 years old (21.6% (IQR: 13.1-31.7). In the remaining groups, seroprevalence ranged from 15.6% (IQR: 8-21.1) to 18.0% (IQR: 13.4-22.6). During monitoring, three (immune) response groups were found: (A) groups with a continuous increase in the proportion of seropositive; (B) those with a slow rate of increase in seroprevalence; and (C) those with a two-phase curve, wherein the initial increase was replaced by a decrease in the percentage of seropositive individuals. A significant correlation was revealed between the number of COVID-19 convalescents and contact persons, and between the number of contacts and healthy seropositive volunteers. Among the seropositive volunteers, more than 93.6% (IQR: 87.1-94.9) were asymptomatic. The results show that the COVID-19 pandemic is accompanied by an increase in seroprevalence, which may be important for the formation of herd immunity.

Serological Testing for COVID-19, Immunological Surveillance, and Exploration of Protective Antibodies

Serological testing is a powerful tool in epidemiological studies for understanding viral circulation and assessing the effectiveness of virus control measures, as is the case of SARS-CoV-2, the pathogenic agent of COVID-19. Immunoassays can quantitatively reveal the concentration of antiviral antibodies. The assessment of antiviral antibody titers may provide information on virus exposure, and changes in IgG levels are also indicative of a reduction in viral circulation. In this work, we describe a serological study for the evaluation of antiviral IgG and IgM antibodies and their correlation with antiviral activity. The serological assay for IgG detection used two SARS-CoV-2 proteins as antigens, the nucleocapsid N protein and the 3CL protease. Cross-reactivity tests in animals have shown high selectivity for detection of antiviral antibodies, using both the N and 3CL antigens. Using samples of human serum from individuals previously diagnosed by PCR for COVID-19, we observed high sensitivity of the ELISA assay. Serological results with human samples also suggest that the combination of higher titers of antiviral IgG antibodies to different antigen targets may be associated with greater neutralization activity, which can be enhanced in the presence of antiviral IgM antibodies.

SARS-CoV-2 Seroprevalence Structure of the Russian Population during the COVID-19 Pandemic

The SARS-CoV-2 pandemic, which came to Russia in March 2020, is accompanied by morbidity level changes and can be tracked using serological monitoring of a representative population sample from Federal Districts (FDs) and individual regions. In a longitudinal cohort study conducted in 26 model regions of Russia, distributed across all FDs, we investigated the distribution and cumulative proportions of individuals with antibodies (Abs) to the SARS-CoV-2 nucleocapsid antigen (Ag), in the period from June to December 2020, using a three-phase monitoring process. In addition, during the formation of the cohort of volunteers, the number of seropositive convalescents, persons who had contact with patients or COVID-19 convalescents, and the prevalence of asymptomatic forms of infection among seropositive volunteers were determined. According to a uniform methodology, 3 mL of blood was taken from the examined individuals, and plasma was separated, from which the presence of Abs to nucleocapsid Ag was determined on a Thermo Scientific Multiascan FC device using the “ELISA anti-SARS-CoV-2 IgG” reagent set (prod. Scientific Center for Applied Microbiology and Biotechnology), in accordance with the developer’s instructions. Volunteers (74,158) were surveyed and divided into seven age groups (1–17, 18–29, 30–39, 40–49, 59–59, 60–69, and 70+ years old), among whom 14,275 were identified as having antibodies to SARS-CoV-2. The average percent seropositive in Russia was 17.8% (IQR: 8.8–23.2). The largest proportion was found among children under 17 years old (21.6% (IQR: 13.1–31.7). In the remaining groups, seroprevalence ranged from 15.6% (IQR: 8–21.1) to 18.0% (IQR: 13.4–22.6). During monitoring, three (immune) response groups were found: (A) groups with a continuous increase in the proportion of seropositive; (B) those with a slow rate of increase in seroprevalence; and (C) those with a two-phase curve, wherein the initial increase was replaced by a decrease in the percentage of seropositive individuals. A significant correlation was revealed between the number of COVID-19 convalescents and contact persons, and between the number of contacts and healthy seropositive volunteers. Among the seropositive volunteers, more than 93.6% (IQR: 87.1–94.9) were asymptomatic. The results show that the COVID-19 pandemic is accompanied by an increase in seroprevalence, which may be important for the formation of herd immunity.

COVID-19 and Progesterone: Part 1.SARS-CoV-2, Progesterone and its potential clinical use

SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) infection is a global medical challenge. Experience based medicines and therapies are being attempted and vaccines are being developed. SARS-CoV-2 exhibits varied patterns of infection and clinical presentations with varied disease outcomes. These attributes are strongly suggestive of some variables that differ among individuals and that affect the course of SARS-CoV-2 infection and symptoms of COVID-19 (Corona Virus Disease of 2019). Sex hormones vary with ageing, between the sexes, among individuals and populations. Sex hormones are known to play a role in immunity and infections. Progesterone is a critical host factor to promote faster recovery following Influenza A virus infection. Anti-inflammatory effects of progesterone are noted. In part 1 of the current study the regulatory role of progesterone for SARS-CoV-2 infection and COVID-19 is analyzed. The role of progesterone at different stages of the SARS CoV-2 infection is investigated with respect to two types of immunity status: immune regulation and immune dysregulation. Progesterone could have various alleviating impacts from SARS-CoV-2 entry till recovery: reversing of hypoxia, stabilizing of blood pressure, controlling thrombosis, balancing electrolytes, reducing the viral load, regulation of immune responses, damage repair, and clearance of debris among others. The present research adds to the available evidence by providing a comprehensive and thorough evaluation of the regulatory role of progesterone in SARS COV-2 infection, COVID-19 pathogenesis, and immune dysregulation. The available evidence has implications for upcoming studies about pathophysiology of COVID-19, as well as the roles of progesterone and other hormones in other infectious diseases.

The trans-omics landscape of COVID-19

The outbreak of coronavirus disease 2019 (COVID-19) is a global health emergency. Various omics results have been reported for COVID-19, but the molecular hallmarks of COVID-19, especially in those patients without comorbidities, have not been fully investigated. Here we collect blood samples from 231 COVID-19 patients, prefiltered to exclude those with selected comorbidities, yet with symptoms ranging from asymptomatic to critically ill. Using integrative analysis of genomic, transcriptomic, proteomic, metabolomic and lipidomic profiles, we report a trans-omics landscape for COVID-19. Our analyses find neutrophils heterogeneity between asymptomatic and critically ill patients. Meanwhile, neutrophils over-activation, arginine depletion and tryptophan metabolites accumulation correlate with T cell dysfunction in critical patients. Our multi-omics data and characterization of peripheral blood from COVID-19 patients may thus help provide clues regarding pathophysiology of and potential therapeutic strategies for COVID-19.

Risk factors for SARS-CoV-2 seroprevalence following the first pandemic wave in UK healthcare workers in a large NHS Foundation Trust

BACKGROUND

We aimed to measure SARS-CoV-2 seroprevalence in a cohort of healthcare workers (HCWs) during the first UK wave of the COVID-19 pandemic, explore risk factors associated with infection, and investigate the impact of antibody titres on assay sensitivity.

METHODS

HCWs at Sheffield Teaching Hospitals NHS Foundation Trust (STH) were prospectively enrolled and sampled at two time points. SARS-CoV-2 antibodies were tested using an in-house assay for IgG and IgA reactivity against Spike and Nucleoprotein (sensitivity 99·47%, specificity 99·56%). Data were analysed using three statistical models: a seroprevalence model, an antibody kinetics model, and a heterogeneous sensitivity model.

FINDINGS

As of 12th June 2020, 24·4% (n=311/1275) HCWs were seropositive. Of these, 39·2% (n=122/311) were asymptomatic. The highest adjusted seroprevalence was measured in HCWs on the Acute Medical Unit (41·1%, 95% CrI 30·0-52·9) and in Physiotherapists and Occupational Therapists (39·2%, 95% CrI 24·4-56·5). Older age groups showed overall higher median antibody titres. Further modelling suggests that, for a serological assay with an overall sensitivity of 80%, antibody titres may be markedly affected by differences in age, with sensitivity estimates of 89% in those over 60 years but 61% in those ≤30 years.

INTERPRETATION

HCWs in acute medical units working closely with COVID-19 patients were at highest risk of infection, though whether these are infections acquired from patients or other staff is unknown. Current serological assays may underestimate seroprevalence in younger age groups if validated using sera from older and/or more symptomatic individuals.

RESEARCH IN CONTEXT

Evidence before this study: We searched PubMed for studies published up to March 6th 2021, using the terms "COVID", "SARS-CoV-2", "seroprevalence", and "healthcare workers", and in addition for articles of antibody titres in different age groups against coronaviruses using "coronavirus", "SARS-CoV-2, "antibody", "antibody tires", "COVID" and "age". We included studies that used serology to estimate prevalence in healthcare workers. SARS-CoV-2 seroprevalence has been shown to be greater in healthcare workers working on acute medical units or within domestic services. Antibody levels against seasonal coronaviruses, SARS-CoV and SARS-CoV-2 were found to be higher in older adults, and patients who were hospitalised.Added value of this study: In this healthcare worker seroprevalence modelling study at a large NHS foundation trust, we confirm that those working on acute medical units, COVID-19 "Red Zones" and within domestic services are most likely to be seropositive. Furthermore, we show that physiotherapists and occupational therapists have an increased risk of COVID-19 infection. We also confirm that antibody titres are greater in older individuals, even in the context of non-hospitalised cases. Importantly, we demonstrate that this can result in age-specific sensitivity in serological assays, where lower antibody titres in younger individuals results in lower assay sensitivity.Implications of all the available evidence: There are distinct occupational roles and locations in hospitals where the risk of COVID-19 infection to healthcare workers is greatest, and this knowledge should be used to prioritise infection prevention control and other measures to protect healthcare workers. Serological assays may have different sensitivity profiles across different age groups, especially if assay validation was undertaken using samples from older and/or hospitalised patients, who tend to have higher antibody titres. Future seroprevalence studies should consider adjusting for age-specific assay sensitivities to estimate true seroprevalence rates.

AUTHOR CONTRIBUTIONS

Modulation of Host Immune Response Is an Alternative Strategy to Combat SARS-CoV-2 Pathogenesis

The novel SARS-CoV-2virus that caused the disease COVID-19 is currently a pandemic worldwide. The virus requires an alveolar type-2 pneumocyte in the host to initiate its life cycle. The viral S1 spike protein helps in the attachment of the virus on toACE-2 receptors present on type-2 pneumocytes, and the S2 spike protein helps in the fusion of the viral membrane with the host membrane. Fusion of the SARS-CoV-2virus and host membrane is followed by entry of viral RNA into the host cells which is directly translated into the replicase-transcriptase complex (RTC) following viral RNA and structural protein syntheses. As the virus replicates within type-2 pneumocytes, the host immune system is activated and alveolar macrophages start secreting cytokines and chemokines, acting as an inflammatory mediator, and chemotactic neutrophils, monocytes, natural NK cells, and CD8+ T cells initiate the local phagocytosis of infected cells. It is not the virus that kills COVID-19 patients; instead, the aberrant host immune response kills them. Modifying the response from the host immune system could reduce the high mortality due to SARS-CoV-2 infection. The present study examines the viral life cycle intype-2 pneumocytes and resultant host immune response along with possible therapeutic targets.

Diagnostic performance of COVID-19 serological assays during early infection: A systematic review and meta-analysis of 11 516 samples

OBJECTIVE

The use of coronavirus disease 2019 (COVID-19) serological testing to diagnose acute infection or determine population seroprevalence relies on understanding assay accuracy during early infection. We aimed to evaluate the diagnostic performance of serological testing in COVID-19 by providing summary sensitivity and specificity estimates with time from symptom onset.

METHODS

A systematic search of Ovid MEDLINE, Embase, Cochrane Central Register of Controlled Trials (CENTRAL) and PubMed was performed up to May 13, 2020. All English language, original peer-reviewed publications reporting the diagnostic performance of serological testing vis-à-vis virologically confirmed SARS-CoV-2 infection were included.

RESULTS

Our search yielded 599 unique publications. A total of 39 publications reporting 11 516 samples from 8872 human participants met eligibility criteria for inclusion in our study. Pooled percentages of IgM and IgG seroconversion by Day 7, 14, 21, 28 and after Day 28 were 37.5%, 73.3%, 81.3%, 72.3% and 73.3%, and 35.4%, 80.6%, 93.3%, 84.4% and 98.9%, respectively. By Day 21, summary estimate of IgM sensitivity was 0.872 (95% CI: 0.784-0.928) and specificity 0.973 (95% CI: 0.938-0.988), while IgG sensitivity was 0.913 (95% CI: 0.823-0.959) and specificity 0.960 (95% CI: 0.919-0.980). On meta-regression, IgM and IgG test accuracy was significantly higher at Day 14 using enzyme-linked immunosorbent assay (ELISA) compared to other methods.

CONCLUSIONS

Serological assays offer imperfect sensitivity for the diagnosis of acute SARS-CoV-2 infection. Estimates of population seroprevalence during or shortly after an outbreak will need to adjust for the delay between infection, symptom onset and seroconversion.

Metabolic reprogramming and immune regulation in viral diseases

The recent outbreak and transmission of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) worldwide and the ensuing coronavirus disease 2019 (COVID-19) pandemic has left us scrambling for ways to contain the disease and develop vaccines that are safe and effective. Equally important, understanding the impact of the virus on the host system in convalescent patients, healthy otherwise or with co-morbidities, is expected to aid in developing effective strategies in the management of patients afflicted with the disease. Viruses possess the uncanny ability to redirect host metabolism to serve their needs and also limit host immune response to ensure their survival. An ever-increasingly powerful approach uses metabolomics to uncover diverse molecular signatures that influence a wide array of host signalling networks in different viral infections. This would also help integrate experimental findings from individual studies to yield robust evidence. In addition, unravelling the molecular mechanisms harnessed by both viruses and tumours in their host metabolism will help broaden the repertoire of therapeutic tools available to combat viral disease.

Over 1-year duration and age difference of SARS-CoV-2 antibodies in convalescent COVID-19 patients

Anti‐severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) immunoglouilin G (IgG) and immunoglouilin M (IgM) antibodies have been widely used to assist clinical diagnosis. Our previous study reported a discrepancy in SARS‐CoV‐2 antibody response between male and female coronavirus disease 2019 (COVID‐19) patients. However, the duration and discrepancy between ages as well as sexes of SARS‐CoV‐2 antibody in convalescent COVID‐19 patients have not been clarified. In this study, a total of 538 health‐examination individuals who were confirmed with SARS‐CoV‐2 infection a year ago were enrolled. Blood samples were collected and detected for IgM and IgG antibodies. Among these convalescent patients, 12.80% were detected positive for IgM antibodies. The positive rates for IgM antibody were close between sexes: for males, this is 9.17% and for females 13.75%. However, the IgG antibody was detected positive in as much as 82.90% convalescent patients and the positive rates were nearly the same between males (82.57%) and females (82.98%). Besides this, the level of IgM and IgG antibodies showed no difference between male and female convalescent patients. The level of IgG antibodies showed a significant difference between ages. The elder patients (over 35 years old) maintained a higher level of IgG antibody than the younger patients (under or equal 35 years old) after recovering for 1 year. In addition, IgG antibody was more vulnerable to disappear in younger patients than in elder patients. Overall, our study identified over 1‐year duration of SARS‐CoV‐2 antibody and age difference of IgG antibody response in convalescent COVID‐19 patients. These findings may provide new insights into long‐term humoral immune response, vaccines efficacy and age‐based personalized vaccination strategies.

Anti‐SARS‐CoV‐2 IgG antibody could maintain over 1‐year in most convalescent COVID‐19 patients.

Anti‐SARS‐CoV‐2 IgG antibody responses may be different between young and elder convalescent COVID‐19 patients.

Development of spike protein-based fluorescence lateral flow assay for the simultaneous detection of SARS-CoV-2 specific IgM and IgG

The pandemic outbreak of the 2019 coronavirus disease (COVID-19), which is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is still spreading rapidly and poses a great threat to human health. As such, developing rapid and accurate immunodiagnostic methods for the identification of infected persons is needed. Here, we proposed a simple but sensitive on-site testing method based on spike protein-conjugated quantum dot (QD) nanotag-integrated lateral flow immunoassay (LFA) to simultaneously detect SARS-CoV-2-specific IgM and IgG in human serum. Advanced silica-core@dual QD-shell nanocomposites (SiO2@DQD) with superior luminescence and stability were prepared to serve as fluorescent nanotags in the LFA strip and guarantee high sensitivity and reliability of the assay. The performance of the SiO2@DQD-strip was fully optimized and confirmed by using 10 positive serum samples from COVID-19 patients and 10 negative samples from patients with other respiratory diseases. The practical clinical value of the assay was further evaluated by testing 316 serum samples (114 positive and 202 negative samples). The overall detection sensitivity and specificity reached 97.37% (111/114) and 95.54% (193/202), respectively, indicating the huge potential of our proposed method for the rapid and accurate detection of SARS-CoV-2-infected persons and asymptomatic carriers.

sMAdCAM: IL-6 Ratio Influences Disease Progression and Anti-Viral Responses in SARS-CoV-2 Infection

The role of sMAdCAM, an important gut immune migratory marker, remains unexplored in COVID-19 pathogenesis considering recent studies positing the gut as a sanctuary site for SARS-CoV-2 persistence. Thus, assimilating profiles of systemic inflammatory mediators with sMAdCAM levels may provide insights into the progression of COVID-19 disease. Also, the role of these markers in governing virus specific immunity following infection remains largely unexplored. A cohort (n = 84) of SARS-C0V-2 infected individuals included a group of in-patients (n = 60) at various stages of disease progression together with convalescent individuals (n = 24) recruited between April and June 2020 from Mumbai, India. Follow-up of 35 in-patients at day 7 post diagnosis was carried out. Th1/Th2/Th17 cytokines along with soluble MAdCAM (sMAdCAM) levels in plasma were measured. Also, anti-viral humoral response as measured by rapid antibody test (IgG, IgM), Chemiluminescent Immunoassay (IgG), and antibodies binding to SARS-CoV-2 proteins were measured by Surface Plasmon Resonance (SPR) from plasma. IL-6 and sMAdCAM levels among in-patients inversely correlated with one another. When expressed as a novel integrated marker—sMIL index (sMAdCAM/IL-6 ratio)—these levels were incrementally and significantly higher in various disease states with convalescents exhibiting the highest values. Importantly, sMAdCAM levels as well as sMIL index (fold change) correlated with peak association response units of receptor binding domain and fold change in binding to spike respectively as measured by SPR. Our results highlight key systemic and gut homing parameters that need to be monitored and investigated further to optimally guide therapeutic and prophylactic interventions for COVID-19.