Development and Evaluation of a Multiplexed Immunoassay for Simultaneous Detection of Serum IgG Antibodies to Six Human Coronaviruses

COVID-19 Virus Structural Details: Optical and Electrochemical Detection

The increasing viral species have ruined people's health and the world's economy. Therefore, it is urgent to design bio-responsive materials to provide a vast platform for detecting a different family's passive or active virus. One can design a reactive functional unit for that moiety based on the particular bio-active moieties in viruses. Nanomaterials as optical and electrochemical biosensors have enabled better tools and devices to develop rapid virus detection. Various material science platforms are available for real-time monitoring and detecting COVID-19 and other viral loads. In this review, we discuss the recent advances of nanomaterials in developing the tools for optical and electrochemical sensing COVID-19. In addition, nanomaterials used to detect other human viruses have been studied, providing insights for developing COVID-19 sensing materials. The basic strategies for nanomaterials develop as virus sensors, fabrications, and detection performances are studied. Moreover, the new methods to enhance the virus sensing properties are discussed to provide a gateway for virus detection in variant forms. The study will provide systematic information and working of virus sensors. In addition, the deep discussion of structural properties and signal changes will offer a new gate for researchers to develop new virus sensors for clinical applications.

Coronavirus spike protein-specific antibodies indicate frequent infections and reinfections in infancy and among BNT162b2-vaccinated healthcare workers

The prevalence of seasonal human coronavirus (HCoV) infections in early childhood and adults has not been well analyzed in longitudinal serological studies. Here we analyzed the changes in HCoV (229E, HKU1, NL63, OC43, MERS, and SARS-CoV-2) spike-specific antibody levels in follow-up serum specimens of 140 children at the age of 1, 2, and 3 years, and of 113 healthcare workers vaccinated for Covid-19 with BNT162b2-vaccine. IgG antibody levels against six recombinant HCoV spike subunit 1 (S1) proteins were measured by enzyme immunoassay. We show that by the age of three years the cumulative seropositivity for seasonal HCoVs increased to 38-81% depending on virus type. BNT162b2 vaccinations increased anti-SARS-CoV-2 S1 antibodies, but no increase in seasonal coronavirus antibodies associated with vaccinations. In healthcare workers (HCWs), during a 1-year follow-up, diagnostic antibody rises were seen in 5, 4 and 14% of the cases against 229E, NL63 and OC43 viruses, respectively, correlating well with the circulating HCoVs. In 6% of the HCWs, a diagnostic antibody rise was seen against S1 of HKU1, however, these rises coincided with anti-OC43 S1 antibody rises. Rabbit and guinea pig immune sera against HCoV S1 proteins indicated immunological cross-reactivity within alpha-CoV (229E and NL63) and beta-CoV (HKU1 and OC43) genera.

Recent advances in immunoassay technologies for the detection of human coronavirus infections

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is the seventh coronavirus (CoV) that has spread in humans and has become a global pandemic since late 2019. Efficient and accurate laboratory diagnostic methods are one of the crucial means to control the development of the current pandemic and to prevent potential future outbreaks. Although real-time reverse transcription-polymerase chain reaction (rRT-PCR) is the preferred laboratory method recommended by the World Health Organization (WHO) for diagnosing and screening SARS-CoV-2 infection, the versatile immunoassays still play an important role for pandemic control. They can be used not only as supplemental tools to identify cases missed by rRT-PCR, but also for first-line screening tests in areas with limited medical resources. Moreover, they are also indispensable tools for retrospective epidemiological surveys and the evaluation of the effectiveness of vaccination. In this review, we summarize the mainstream immunoassay methods for human coronaviruses (HCoVs) and address their benefits, limitations, and applications. Then, technical strategies based on bioinformatics and advanced biosensors were proposed to improve the performance of these methods. Finally, future suggestions and possibilities that can lead to higher sensitivity and specificity are provided for further research.

SARS-CoV-2-specicific humoral immunity in convalescent patients with mild COVID-19 is supported by CD4+ T-cell help and negatively correlated with Alphacoronavirus-specific antibody titer

This study aimed at investigating the nature of SARS-CoV-2-specific immunity in patients with mild COVID-19 and sought to identify parameters most relevant for the generation of neutralizing antibody responses in convalescent COVID-19 patients. In the majority of the examined patients a cellular as well as humoral immune response directed to SARS-CoV-2 was detected. The finding of an anti-SARS-CoV-2-reactive cellular immune response in healthy individuals suggests a pre-existing immunity to various common cold HCoVs which share close homology with SARS-CoV-2. The humoral immunity to the S protein of SARS-CoV-2 detected in convalescent COVID-19 patients correlates with the presence of SARS-CoV-2-reactive CD4⁺ T cells expressing T_h1 cytokines. Remarkably, an inverse correlation of SARS-CoV-2 S protein-specific IgGs with HCoV-NL63 and HCoV-229E S1 protein-specific IgGs suggests that pre-existing immunity to Alphacoronaviruses might have had an inhibitory imprint on the immune response to SARS-CoV-2-infection in the examined patients with mild COVID-19.

Association between IgG responses against the nucleocapsid proteins of alphacoronaviruses and COVID-19 severity

Understanding immune responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is crucial to contain the COVID-19 pandemic. Using a multiplex approach, serum IgG responses against the whole SARS-CoV-2 proteome and the nucleocapsid proteins of endemic human coronaviruses (HCoVs) were measured in SARS-CoV-2-infected donors and healthy controls. COVID-19 severity strongly correlated with IgG responses against the nucleocapsid (N) of SARS-CoV-2 and possibly with the number of viral antigens targeted. Furthermore, a strong correlation between COVID-19 severity and serum responses against N of endemic alpha- but not betacoronaviruses was detected. This correlation was neither caused by cross-reactivity of antibodies, nor by a general boosting effect of SARS-CoV-2 infection on pre-existing humoral immunity. These findings raise the prospect of a potential disease progression marker for COVID-19 severity that allows for early stratification of infected individuals.

Serological Follow-Up Study Indicates High Seasonal Coronavirus Infection and Reinfection Rates in Early Childhood

Seasonal human coronaviruses (HCoVs) cause respiratory infections, especially in children. Currently, the knowledge on early childhood seasonal coronavirus infections and the duration of antibody levels following the first infections is limited. Here we analyzed serological follow-up samples to estimate the rate of primary infection and reinfection(s) caused by seasonal coronaviruses in early childhood. Serum specimens were collected from 140 children at ages of 13, 24, and 36 months (1, 2, and 3 years), and IgG antibody levels against recombinant HCoV nucleoproteins (N) were measured by enzyme immunoassay (EIA). Altogether, 84% (118/140) of the children were seropositive for at least one seasonal coronavirus N by the age of 3 years. Cumulative seroprevalences for HCoVs 229E, HKU1, NL63, and OC43 increased by age, and they were 45%, 27%, 70%, and 44%, respectively, at the age of 3 years. Increased antibody levels between yearly samples indicated reinfections by 229E, NL63, and OC43 viruses in 20-48% of previously seropositive children by the age of 3 years. Antibody levels declined 54-73% or 31-77% during the year after seropositivity in children initially seropositive at 1 or 2 years of age, respectively, in case there was no reinfection. The correlation of 229E and NL63, and OC43 and HKU1 EIA results, suggested potential cross-reactivity between the N specific antibodies inside the coronavirus genera. The data shows that seasonal coronavirus infections and reinfections are common in early childhood and the antibody levels decline relatively rapidly. IMPORTANCE The rapid spread of COVID-19 requires better knowledge on the rate of coronavirus infections and coronavirus specific antibody responses in different population groups. In this work we analyzed changes in seasonal human coronavirus specific antibodies in young children participating in a prospective 3-year serological follow-up study. We show that based on seropositivity and changes in serum coronavirus antibody levels, coronavirus infections and reinfections are common in early childhood and the antibodies elicited by the infection decline relatively rapidly. These observations provide further information on the characteristics of humoral immune responses of coronavirus infections in children.

Visualization and analysis of mapping knowledge domains for coronavirus research

BACKGROUND

In recent years, many countries around the world have been threatened by COVs. The aim of this study was to better grasp developments and trends in research on coronavirus around the world and to promote theoretical research into their prevention and control.

METHODS

Research on coronavirus was reviewed and analyzed using bibliometrics based on a total of 4860 publications collected from the Web of Science Core Collection database. Yearly quantitative distribution of literature, country/region distribution, organization distribution, main source journal distribution, subject category distribution, research knowledge bases, and research hotspots and frontiers were all analyzed, and CiteSpace and VOSviewer were used to plot knowledge domain maps, Excel was used to plot keyword strategy diagram.

RESULTS

Coronavirus research could be roughly divided into 4 stages: preliminary development stage (before 2000), rapid growth stage (2000-2005), slow decline stage (2006-2011) and sustained growth stage (since 2012). America had taken the leading position in this field. The study of COVs involves many subject categories, mainly includes virology, veterinary sciences, biology, and immunology. At present, the key words in the field of coronavirus research were mainly divided into 6 major hot clusters, namely, the introduction and structure analysis of coronavirus, the research on the outbreak source and transmission of coronavirus, the research on the infection pathway of coronavirus in human body, the research on the pathogenesis of coronavirus, the research on the diagnosis and symptoms of coronavirus infection, and the research on the treatment of coronavirus.

CONCLUSION

Coronavirus, which occurs all over the world, often causes huge casualties and economic losses, and poses a serious threat to the safe and stable operation of the social and economic system. Objective literature review and analysis can help scholars in related fields to deepen their overall understanding. And, there are several key issues that should be further explored in future research.

Development of an Indirect ELISA for the Detection of SARS-CoV-2 Antibodies in Cats

Companion animals are susceptible to a variety of coronaviruses, and recent studies show that felines are highly susceptible to SARS-CoV-2 infection. RT-PCR diagnostic is currently the method of choice to detect the presence of SARS-CoV-2-specific viral nucleic acids in animal samples during an active infection; however, serological assays are critical to determine whether animals were exposed to the virus and to determine the seroprevalence of SARS-CoV-2-specific antibodies in a defined population. In this study, we utilized recombinant nucleocapsid (N) protein and the receptor-binding domain (RBD) of the spike protein of SARS-CoV-2 expressed in E. coli (N) and mammalian cells (N, RBD) to develop indirect ELISA (iELISA) tests using well-characterized SARS-CoV-2-positive and -negative cat serum panels from previous experimental cat challenge studies. The optimal conditions for the iELISA tests were established based on checkerboard dilutions of antigens and antibodies. The diagnostic sensitivity for the detection of feline antibodies specific for the N or RBD proteins of the iELISA tests was between 93.3 and 97.8%, respectively, and the diagnostic specificity 95.5%. The iELISAs developed here can be used for high-throughput screening of cat sera for both antigens. The presence of SARS-CoV-2-specific antibodies in a BSL-2 biocontainment environment, unlike virus neutralization tests with live virus which have to be performed in BSL-3 laboratories.

An all-in-one point-of-care testing device for multiplexed detection of respiratory infections

The impact of the COVID-19 pandemic has reinforced the need for rapid, cost-effective, and reliable point-of-care testing (POCT) devices for massive population screening. The co-circulation of SARS-CoV-2 with several seasonal respiratory viruses highlights the need for multiplexed biosensing approaches. Herein, we present a fast and robust all-in-one POCT device for parallel viral antigen and serological analysis. The biosensing approach consists of a functionalized polycarbonate disc-shaped surface with microfluidic structures, where specific bioreagents are immobilized in microarray format, and a portable optoelectronic analyzer. The biosensor quantifies the concentration of viral antigens and specific immunoglobulins G and M for SARS-CoV-2, influenza A/B, adenovirus, and respiratory syncytial virus, using 30 μL of a sample. The semi-automated analysis of 6 samples is performed in 30 min. Validation studies performed with 135 serum samples and 147 nasopharyngeal specimens reveal high diagnostic sensitivity (98–100%) and specificity (84–98%), achieving an excellent agreement (κ = 0.937) with commercial immunoassays, which complies with the World Health Organization criteria for POC COVID-19 diagnostic tests. The versatility of the POCT device paves the way for the detection of other pathogens and analytes in the incoming post-pandemic world, integrating specific bioreagents against different variants of concerns and interests.

Immunity to SARS-CoV-2 induced by infection or vaccination

Adaptive immune responses play critical roles in viral clearance and protection against re-infection, and SARS-CoV-2 is no exception. What is exceptional is the rapid characterization of the immune response to the virus performed by researchers during the first 20 months of the pandemic. This has given us a more detailed understanding of SARS-CoV-2 compared to many viruses that have been with us for a long time. Furthermore, effective COVID-19 vaccines were developed in record time, and their rollout worldwide is already making a significant difference, although major challenges remain in terms of equal access. The pandemic has engaged scientists and the public alike, and terms such as seroprevalence, neutralizing antibodies, antibody escape and vaccine certificates have become familiar to a broad community. Here, we review key findings concerning B cell and antibody (Ab) responses to SARS-CoV-2, focusing on non-severe cases and anti-spike (S) Ab responses in particular, the latter being central to protective immunity induced by infection or vaccination. The emergence of viral variants that have acquired mutations in S acutely highlights the need for continued characterization of both emerging variants and Ab responses against these during the evolving pathogen-immune system arms race.

Humoral immune response to COVID-19 infection or vaccination among celiac disease patients

Introduction

Celiac disease (CD) is the most common autoimmune disease (AD) of the small intestine, affecting 1-2% of the population globally. It is characterized by the serological presence of autoantibodies (Abs), tissue transglutaminase antibody (tTGA), immunoglobulin (Ig) A, and IgG. Production of antibodies against SARS-CoV-2 after infection with the virus or vaccination is not well understood, especially among CD patients. The goal of this study was to measure the IgG antibodies in Jordanian patients infected with or vaccinated against the SARS-CoV-2 virus with different types of vaccines (Pfizer- BioNTech BNT162b2, Sinopharm BBIBP-CorV or Oxford-AstraZeneca ChAdOx1-S) and compare them with the levels in non-celiac controls. IgG levels induced by different vaccines were also compared.

Material and methods

The data for this cross-sectional study were obtained via a survey, whereby respondents were identified through convenience sampling. The healthy controls were given Questionnaire A while CD patients completed Questionnaire B. The blood samples from all participants were tested for the COVID-19 nucleocapsid protein (NP) IgG serum levels for participants previously infected with SARS-CoV-2, and spike (S) protein (S1/S2) IgG serum levels for vaccine recipients.

Results

The study involved 116 individuals, 60 (51.7%) of whom were CD patients. The NP IgG serum levels in the infected and S1/S2 IgG levels in the vaccinated CD patients were significantly lower than the levels in controls (48.3 ±44.5 vs. 81.1 ±34.4 and 49 ±45.8 vs. 75.7 ±38.6, p = 0.002). Moreover, only the Pfizer vaccine induced significantly more IgG antibodies in controls compared to CD patients (88.8 ±29.1 vs. 58.3 ±45.4, p = 0.01). On the other hand, the IgG levels were significantly higher in CD patients who received the Pfizer relative to the AstraZeneca vaccine (58.3 ±45.5 vs. 13.0 ±23.6, p = 0.03). After adjusting for presence of CD, age, sex, body mass index (BMI), comorbidities, vaccine type, smoking, gluten adherence, and time since infection or vaccination, SARS-CoV-2 S1/S2 IgG Abs and/or NP IgG Abs positivity was significantly associated with CD absence and negatively with vaccine type (AstraZeneca) with the odds ratios (ORs) of 9.6 (95% CI = 1.5-59.2, p = 0.015) and 0.03 (95% CI = 0.004-0.244. p = 0.001), respectively.

Conclusions

We concluded that patients with CD had lower SARS-CoV-2 S1/S2 IgG Abs and NP IgG Abs levels than controls, and CD patients who received the Pfizer vaccine had higher IgG levels than patients who received the AstraZeneca vaccine. We recommend that further research be conducted to address the dynamics of the antibody responses in CD patients regarding COVID-19 infection.

A Highly Sensitive and Specific SARS-CoV-2 Spike- and Nucleoprotein-Based Fluorescent Multiplex Immunoassay (FMIA) to Measure IgG, IgA, and IgM Class Antibodies

Validation and standardization of accurate serological assays are crucial for the surveillance of the coronavirus disease 2019 (COVID-19) pandemic and population immunity. We describe the analytical and clinical performance of an in-house fluorescent multiplex immunoassay (FMIA) for simultaneous quantification of antibodies against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleoprotein and spike glycoprotein. Furthermore, we calibrated IgG-FMIA against World Health Organization (WHO) International Standard and compared FMIA results to an in-house enzyme immunoassay (EIA) and a microneutralization test (MNT). We also compared the MNT results of two laboratories. IgG-FMIA displayed 100% specificity and sensitivity for samples collected 13 to 150 days post-onset of symptoms (DPO). For IgA- and IgM-FMIA, 100% specificity and sensitivity were obtained for a shorter time window (13 to 36 and 13 to 28 DPO for IgA- and IgM-FMIA, respectively). FMIA and EIA results displayed moderate to strong correlation, but FMIA was overall more specific and sensitive. IgG-FMIA identified 100% of samples with neutralizing antibodies (NAbs). Anti-spike IgG concentrations correlated strongly (ρ = 0.77 to 0.84, P < 2.2 × 10-16) with NAb titers, and the two laboratories' NAb titers displayed a very strong correlation (ρ = 0.95, P < 2.2 × 10-16). Our results indicate good correlation and concordance of antibody concentrations measured with different types of in-house SARS-CoV-2 antibody assays. Calibration against the WHO international standard did not, however, improve the comparability of FMIA and EIA results. IMPORTANCE SARS-CoV-2 serological assays with excellent clinical performance are essential for reliable estimation of the persistence of immunity after infection or vaccination. In this paper we present a thoroughly validated SARS-CoV-2 serological assay with excellent clinical performance and good comparability to neutralizing antibody titers. Neutralization tests are still considered the gold standard for SARS-CoV-2 serological assays, but our assay can identify samples with neutralizing antibodies with 100% sensitivity and 96% specificity without the need for laborious and slow biosafety level 3 (BSL-3) facility-requiring analyses.

Relative Ratios of Human Seasonal Coronavirus Antibodies Predict the Efficiency of Cross-Neutralization of SARS-CoV-2 Spike Binding to ACE2

BACKGROUND

Antibodies raised against human seasonal coronaviruses (sCoVs), which are responsible for the common cold, are known to cross-react with SARS-CoV-2 antigens. This prompts questions about their protective role against SARS-CoV-2 infections and COVID-19 severity. However, the relationship between sCoVs exposure and SARS-CoV-2 correlates of protection are not clearly identified.

METHODS

We performed a cross-sectional analysis of cross-reactivity and cross-neutralization to SARS-CoV-2 antigens (S-RBD, S-trimer, N) using pre-pandemic sera from four different groups: pediatrics and adolescents, individuals 21 to 70 years of age, older than 70 years of age, and individuals living with HCV or HIV. Data was then further analysed using machine learning to identify predictive patterns of neutralization based on sCoVs serology.

FINDINGS

Antibody cross-reactivity to SARS-CoV-2 antigens varied between 1.6% and 15.3% depending on the cohort and the isotype-antigen pair analyzed. We also show a range of neutralizing activity (0-45%) with median inhibition ranging from 17.6 % to 23.3 % in serum that interferes with SARS-CoV-2 spike attachment to ACE2 independently of age group. While the abundance of sCoV antibodies did not directly correlate with neutralization, we show that neutralizing activity is rather dependent on relative ratios of IgGs in sera directed to all four sCoV spike proteins. More specifically, we identified antibodies to NL63 and OC43 as being the most important predictors of neutralization.

INTERPRETATION

Our data support the concept that exposure to sCoVs triggers antibody responses that influence the efficiency of SARS-CoV-2 spike binding to ACE2, which may potentially impact COVID-19 disease severity through other latent variables.

FUNDING

This study was supported by a grant by the CIHR (VR2 -172722) and by a grant supplement by the CITF, and by a NRC Collaborative R&D Initiative Grant (PR031-1).

Original antigenic sin responses to Betacoronavirus spike proteins are observed in a mouse model, but are not apparent in children following SARS-CoV-2 infection

Background

The effects of pre-existing endemic human coronavirus (HCoV) immunity on SARS-CoV-2 serologic and clinical responses are incompletely understood.

Objectives

We sought to determine the effects of prior exposure to HCoV Betacoronavirus HKU1 spike protein on serologic responses to SARS-CoV-2 spike protein after intramuscular administration in mice. We also sought to understand the baseline seroprevalence of HKU1 spike antibodies in healthy children and to measure their correlation with SARS-CoV-2 binding and neutralizing antibodies in children hospitalized with acute coronavirus disease 2019 (COVID-19) or multisystem inflammatory syndrome (MIS-C).

Methods

Groups of 5 mice were injected intramuscularly with two doses of alum-adjuvanted HKU1 spike followed by SARS-CoV-2 spike; or the reciprocal regimen of SARS-Cov-2 spike followed by HKU1 spike. Sera collected 21 days following each injection was analyzed for IgG antibodies to HKU1 spike, SARS-CoV-2 spike, and SARS-CoV-2 neutralization. Sera from children hospitalized with acute COVID-19, MIS-C or healthy controls (n = 14 per group) were analyzed for these same antibodies.

Results

Mice primed with SARS-CoV-2 spike and boosted with HKU1 spike developed high titers of SARS-CoV-2 binding and neutralizing antibodies; however, mice primed with HKU1 spike and boosted with SARS-CoV-2 spike were unable to mount neutralizing antibodies to SARS-CoV-2. HKU1 spike antibodies were detected in all children with acute COVID-19, MIS-C, and healthy controls. Although children with MIS-C had significantly higher HKU1 spike titers than healthy children (GMT 37239 vs. 7551, P = 0.012), these titers correlated positively with both SARS-CoV-2 binding (r = 0.7577, P<0.001) and neutralizing (r = 0.6201, P = 0.001) antibodies.

Conclusions

Prior murine exposure to HKU1 spike protein completely impeded the development of neutralizing antibodies to SARS-CoV-2, consistent with original antigenic sin. In contrast, the presence of HKU1 spike IgG antibodies in children with acute COVID-19 or MIS-C was not associated with diminished neutralizing antibody responses to SARS-CoV-2.

The next-generation coronavirus diagnostic techniques with particular emphasis on the SARS-CoV-2

The potential zoonotic coronaviruses (SARS-CoV, MERS-CoV, and SARS-CoV-2) are of global health concerns. Early diagnosis is the milestone in their mitigation, control, and eradication. Many diagnostic techniques are showing great success and have many advantages, such as the rapid turnover of the results, high accuracy, and high specificity and sensitivity. However, some of these techniques have several pitfalls if samples were not collected, processed, and transported in the standard ways and if these techniques were not practiced with extreme caution and precision. This may lead to false-negative/positive results. This may affect the downstream management of the affected cases. These techniques require regular fine-tuning, upgrading, and optimization. The continuous evolution of new strains and viruses belong to the coronaviruses is hampering the success of many classical techniques. There are urgent needs for next generations of coronaviruses diagnostic assays that overcome these pitfalls. This new generation of diagnostic tests should be able to do simultaneous, multiplex, and high-throughput detection of various coronavirus in one reaction. Furthermore, the development of novel assays and techniques that enable the in situ detection of the virus on the environmental samples, especially air, water, and surfaces, should be given considerable attention in the future. These approaches will have a substantial positive impact on the mitigation and eradication of coronaviruses, including the current SARS-CoV-2 pandemic.

Seroprevalence and SARS-CoV-2 cross-reactivity of endemic coronavirus OC43 and 229E antibodies in Finnish children and adults

Endemic human coronaviruses (hCoVs) are common causative agents of respiratory tract infections, affecting especially children. However, in the ongoing SARS-CoV-2 pandemic, children are the least affected age-group. The objective of this study was to investigate the magnitude of endemic hCoVs antibodies in Finnish children and adults, and pre-pandemic antibody cross-reactivity with SARS-CoV-2. Antibody levels against endemic hCoVs start to rise at a very early age, reaching to overall 100% seroprevalence. No difference in the antibody levels was detected for OC43 but the magnitude of 229E-specific antibodies was significantly higher in the sera of children. OC43 and 229E hCoV antibody levels of children correlated significantly with each other and with the level of cross-reactive SARS-CoV-2 antibodies, whereas these correlations completely lacked in adults. Although none of the sera showed SARS-CoV-2 neutralization, the higher overall hCoV cross-reactivity observed in children might, at least partially, contribute in controlling SARS-CoV-2 infection in this population.

Immunogenicity and crossreactivity of antibodies to the nucleocapsid protein of SARS-CoV-2: utility and limitations in seroprevalence and immunity studies

COVID-19 patients elicit strong responses to the nucleocapsid (N) protein of SARS-CoV-2 but binding antibodies are also detected in prepandemic individuals, indicating potential crossreactivity with common cold human coronaviruses (HCoV) and questioning its utility in seroprevalence studies. We investigated the immunogenicity of the full-length and shorter fragments of the SARS-CoV-2 N protein, and the crossreactivity of antibodies with HCoV. We identified a C-terminus region in SARS-CoV2 N of minimal sequence homology with HCoV that was more specific for SARS-CoV-2 and highly immunogenic. IgGs to the full-length SARS-CoV-2 N also recognized N229E N, and IgGs to HKU1 N recognized SARS-CoV-2 N. Crossreactivity with SARS-CoV-2 was stronger for alpha- rather than beta-HCoV despite having less sequence identity, revealing the importance of conformational recognition. Higher preexisting IgG to OC43 N correlated with lower IgG to SARS-CoV-2 N in rRT-PCR negative individuals, reflecting less exposure and indicating a potential protective association. Antibodies to SARS-CoV-2 N were higher in patients with more severe and longer duration of symptoms and in females. IgGs remained stable for at least 3 months, while IgAs and IgMs declined faster. In conclusion, N protein is a primary target of SARS-CoV-2-specific and HCoV crossreactive antibodies, both of which may affect the acquisition of immunity to COVID-19.

Seroprevalence of COVID-19 and associated factors in a medical institution in Pakistan

Objective

This study investigates the association of preventive measures with coronavirus disease (COVID-19) seropositivity.

Methods

This cross-sectional study was conducted at the Combined Military Hospital Kharian Medical College, Pakistan, in September 2020. A total of 442 participants from three different strata (faculty, students, and administration/technical staff) were enrolled using a convenient sampling technique. A rapid antibody testing method was used to detect antibodies. The Ichroma™ COVID-19 Ab test is an in vitro diagnostic device that helps in the rapid identification of COVID-19 by measuring the levels of IgG and IgM antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the blood. An automated fluorescent immunoassay system (AFIAS-6), with a clinical sensitivity of 95.8% and specificity of 96.7%, was used for qualitative analysis. A self-administered questionnaire was used to collect data, and data analysis was performed using SPSS version 25.

Results

In total, 442 participants were included in the study: 40 (9%) faculty members, 299 (67%) students, and 103 (23.3%) administrative/technical staff. As many as 14.9% of the participants were symptomatic; 32.4% always used masks, and 14% never wore masks. Furthermore, 69.7% of participants frequently washed their hands for 20 s, and 75.6% were aware of social distancing. A total of 16.96% of participants tested positive for IgG antibodies. Moreover, most of the administration/technical staff who tested positive for IgG were asymptomatic (68.42%). A significant association (p < 0.001) was found between following the safety guidelines (wearing masks, handwashing, and social distancing) and the occurrence of COVID-19.

Conclusion

This study showed a higher seroprevalence rate than other studies as it was conducted toward the end of the first wave of the COVID-19 pandemic. However, we are still far from achieving herd immunity. Furthermore, strict compliance with preventive measures is the only way to ensure safety until an effective vaccine is developed.

Automated, flow-based chemiluminescence microarray immunoassay for the rapid multiplex detection of IgG antibodies to SARS-CoV-2 in human serum and plasma (CoVRapid CL-MIA)

In the face of the COVID-19 pandemic, the need for rapid serological tests that allow multiplexing emerged, as antibody seropositivity can instruct about individual immunity after an infection with SARS-CoV-2 or after vaccination. As many commercial antibody tests are either time-consuming or tend to produce false negative or false positive results when only one antigen is considered, we developed an automated, flow-based chemiluminescence microarray immunoassay (CL-MIA) that allows for the detection of IgG antibodies to SARS-CoV-2 receptor-binding domain (RBD), spike protein (S1 fragment), and nucleocapsid protein (N) in human serum and plasma in less than 8 min. The CoVRapid CL-MIA was tested with a set of 65 SARS-CoV-2 serology positive or negative samples, resulting in 100% diagnostic specificity and 100% diagnostic sensitivity, thus even outcompeting commercial tests run on the same sample set. Additionally, the prospect of future quantitative assessments (i.e., quantifying the level of antibodies) was demonstrated. Due to the fully automated process, the test can easily be operated in hospitals, medical practices, or vaccination centers, offering a valuable tool for COVID-19 serosurveillance. Graphical abstract.

Current methods for diagnosis of human coronaviruses: pros and cons

The current global fight against coronavirus disease (COVID-19) to flatten the transmission curve is put forth by the World Health Organization (WHO) as there is no immediate diagnosis or cure for COVID-19 so far. In order to stop the spread, researchers worldwide are working around the clock aiming to develop reliable tools for early diagnosis of severe acute respiratory syndrome (SARS-CoV-2) understanding the infection path and mechanisms. Currently, nucleic acid-based molecular diagnosis (real-time reverse transcription polymerase chain reaction (RT-PCR) test) is considered the gold standard for early diagnosis of SARS-CoV-2. Antibody-based serology detection is ineffective for the purpose of early diagnosis, but a potential tool for serosurveys, providing people with immune certificates for clearance from COVID-19 infection. Meanwhile, there are various blooming methods developed these days. In this review, we summarise different types of coronavirus discovered which can be transmitted between human beings. Methods used for diagnosis of the discovered human coronavirus (SARS, MERS, COVID-19) including nucleic acid detection, gene sequencing, antibody detection, antigen detection, and clinical diagnosis are presented. Their merits, demerits and prospects are discussed which can help the researchers to develop new generation of advanced diagnostic tools for accurate and effective control of human coronavirus transmission in the communities and hospitals.

Accurate SARS-CoV-2 seroprevalence surveys require robust multi-antigen assays

There is a plethora of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) serological tests based either on nucleocapsid phosphoprotein (N), S1-subunit of spike glycoprotein (S1) or receptor binding domain (RBD). Although these single-antigen based tests demonstrate high clinical performance, there is growing evidence regarding their limitations in epidemiological serosurveys. To address this, we developed a Luminex-based multiplex immunoassay that detects total antibodies (IgG/IgM/IgA) against the N, S1 and RBD antigens and used it to compare antibody responses in 1225 blood donors across Greece. Seroprevalence based on single-antigen readouts was strongly influenced by both the antigen type and cut-off value and ranged widely [0.8% (95% CI 0.4-1.5%)-7.5% (95% CI 6.0-8.9%)]. A multi-antigen approach requiring partial agreement between RBD and N or S1 readouts (RBD&N|S1 rule) was less affected by cut-off selection, resulting in robust seroprevalence estimation [0.6% (95% CI 0.3-1.1%)-1.2% (95% CI 0.7-2.0%)] and accurate identification of seroconverted individuals.

Canakinumab as treatment for COVID-19-related pneumonia: A prospective case-control study

OBJECTIVES

Canakinumab is an IL-1β antibody that neutralises the activity of IL-1β. This study examined the efficacy and safety of canakinumab in patients with moderate COVID-19-related pneumonia.

DESIGN

This study aimed to evaluate the reduction in duration of hospitalisation with adequate oxygen status. Forty-eight patients with moderate COVID-19-related pneumonia were asked to participate in the prospective case-control study: 33 patients (cases) signed informed consent and received canakinumab (Cohort 1) and 15 patients (Controls) refused to receive the experimental drug and received institutional standard of care (Cohort 2).

RESULTS

Hospital discharge within 21 days was seen in 63% of patients in Cohort 1 vs. 0% in Cohort 2 (median 14 vs. 26 days, respectively; p < 0.001). There was significant clinical improvement in ventilation regimes following administration of canakinumab compared with Cohort 2 (Stuart-Maxwell test for paired data, p < 0.001). Patients treated with canakinumab experienced a significant increase in PaO2:FiO2 (p < 0.001) and reduction in lung damage by CT (p = 0.01), along with significant decreases in immune/inflammation markers that were not observed in Cohort 2. Only mild side-effects were seen in patients treated with canakinumab; survival at 60 days was 90.0% (95% CI 71.9-96.7) in patients treated with canakinumab and 73.3% (95% CI 43.6-89.1) for Cohort 2.

CONCLUSIONS

Treatment with canakinumab in patients with COVID-19-related pneumonia rapidly restored normal oxygen status, decreased the need for invasive mechanical ventilation, and was associated with earlier hospital discharge and favourable prognosis versus standard of care.

On the Challenges for the Diagnosis of SARS-CoV-2 Based on a Review of Current Methodologies

Diagnosis of COVID-19 has been challenging owing to the need for mass testing and for combining distinct types of detection to cover the different stages of the infection. In this review, we have surveyed the most used methodologies for diagnosis of COVID-19, which can be basically categorized into genetic-material detection and immunoassays. Detection of genetic material with real-time polymerase chain reaction (RT-PCR) and similar techniques has been achieved with high accuracy, but these methods are expensive and require time-consuming protocols which are not widely available, especially in less developed countries. Immunoassays for detecting a few antibodies, on the other hand, have been used for rapid, less expensive tests, but their accuracy in diagnosing infected individuals has been limited. We have therefore discussed the strengths and limitations of all of these methodologies, particularly in light of the required combination of tests owing to the long incubation periods. We identified the bottlenecks that prevented mass testing in many countries, and proposed strategies for further action, which are mostly associated with materials science and chemistry. Of special relevance are the methodologies which can be integrated into point-of-care (POC) devices and the use of artificial intelligence that do not require products from a well-developed biotech industry.

Humoral Responses and Serological Assays in SARS-CoV-2 Infections

In December 2019, the novel betacoronavirus Severe Acute Respiratory Disease Coronavirus 2 (SARS-CoV-2) was first detected in Wuhan, China. SARS-CoV-2 has since become a pandemic virus resulting in hundreds of thousands of deaths and deep socioeconomic implications worldwide. In recent months, efforts have been directed towards detecting, tracking, and better understanding human humoral responses to SARS-CoV-2 infection. It has become critical to develop robust and reliable serological assays to characterize the abundance, neutralization efficiency, and duration of antibodies in virus-exposed individuals. Here we review the latest knowledge on humoral immune responses to SARS-CoV-2 infection, along with the benefits and limitations of currently available commercial and laboratory-based serological assays. We also highlight important serological considerations, such as antibody expression levels, stability and neutralization dynamics, as well as cross-reactivity and possible immunological back-boosting by seasonal coronaviruses. The ability to accurately detect, measure and characterize the various antibodies specific to SARS-CoV-2 is necessary for vaccine development, manage risk and exposure for healthcare and at-risk workers, and for monitoring reinfections with genetic variants and new strains of the virus. Having a thorough understanding of the benefits and cautions of standardized serological testing at a community level remains critically important in the design and implementation of future vaccination campaigns, epidemiological models of immunity, and public health measures that rely heavily on up-to-date knowledge of transmission dynamics.

Array-based analysis of SARS-CoV-2, other coronaviruses, and influenza antibodies in convalescent COVID-19 patients

Detection of antibodies to upper respiratory pathogens is critical to surveillance, assessment of the immune status of individuals, vaccine development, and basic biology. The urgent need for antibody detection tools has proven particularly acute in the COVID-19 era. We report a multiplex label-free antigen microarray on the Arrayed Imaging Reflectometry (AIR) platform for detection of antibodies to SARS-CoV-2, SARS-CoV-1, MERS, three circulating coronavirus strains (HKU1, 229E, OC43) and three strains of influenza. We find that the array is readily able to distinguish uninfected from convalescent COVID-19 subjects, and provides quantitative information about total Ig, as well as IgG- and IgM-specific responses.

Nanobiosensors for the Detection of Novel Coronavirus 2019-nCoV and Other Pandemic/Epidemic Respiratory Viruses: A Review

The coronavirus disease 2019 (COVID-19) pandemic is considered a public health emergency of international concern. The 2019 novel coronavirus (2019-nCoV) or severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that caused this pandemic has spread rapidly to over 200 countries, and has drastically affected public health and the economies of states at unprecedented levels. In this context, efforts around the world are focusing on solving this problem in several directions of research, by: (i) exploring the origin and evolution of the phylogeny of the SARS-CoV-2 viral genome; (ii) developing nanobiosensors that could be highly effective in detecting the new coronavirus; (iii) finding effective treatments for COVID-19; and (iv) working on vaccine development. In this paper, an overview of the progress made in the development of nanobiosensors for the detection of human coronaviruses (SARS-CoV, SARS-CoV-2, and Middle East respiratory syndrome coronavirus (MERS-CoV) is presented, along with specific techniques for modifying the surface of nanobiosensors. The newest detection methods of the influenza virus responsible for acute respiratory syndrome were compared with conventional methods, highlighting the newest trends in diagnostics, applications, and challenges of SARS-CoV-2 (COVID-19 causative virus) nanobiosensors.

A systematic review of antibody mediated immunity to coronaviruses: kinetics, correlates of protection, and association with severity

Many public health responses and modeled scenarios for COVID-19 outbreaks caused by SARS-CoV-2 assume that infection results in an immune response that protects individuals from future infections or illness for some amount of time. The presence or absence of protective immunity due to infection or vaccination (when available) will affect future transmission and illness severity. Here, we review the scientific literature on antibody immunity to coronaviruses, including SARS-CoV-2 as well as the related SARS-CoV, MERS-CoV and endemic human coronaviruses (HCoVs). We reviewed 2,452 abstracts and identified 491 manuscripts relevant to 5 areas of focus: 1) antibody kinetics, 2) correlates of protection, 3) immunopathogenesis, 4) antigenic diversity and cross-reactivity, and 5) population seroprevalence. While further studies of SARS-CoV-2 are necessary to determine immune responses, evidence from other coronaviruses can provide clues and guide future research.

Improved Detection of Antibodies against SARS-CoV-2 by Microsphere-Based Antibody Assay

Currently available COVID-19 antibody tests using enzyme immunoassay (EIA) or immunochromatographic assay have variable sensitivity and specificity. Here, we developed and evaluated a novel microsphere-based antibody assay (MBA) for detecting immunoglobulin G (IgG) against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleoprotein (NP) and spike protein receptor binding domain (RBD). The seropositive cutoff value was set using a cohort of 294 anonymous serum specimens collected in 2018. The specificity was assessed using serum specimens collected from organ donors or influenza patients before 2020. Seropositive rate was determined among COVID-19 patients. Time-to-seropositivity and signal-to-cutoff (S/CO) ratio were compared between MBA and EIA. MBA had a specificity of 100% (93/93; 95% confidence interval (CI), 96-100%) for anti-NP IgG, 98.9% (92/93; 95% CI 94.2-100%) for anti-RBD IgG. The MBA seropositive rate for convalescent COVID-19 patients was 89.8% (35/39) for anti-NP IgG and 79.5% (31/39) for anti-RBD IgG. The time-to-seropositivity was shorter with MBA than EIA. MBA could better differentiate between COVID-19 patients and negative controls with higher S/CO ratio for COVID-19 patients, lower S/CO ratio with negative controls and fewer specimens in the equivocal range. MBA is robust, simple and is suitable for clinical microbiology laboratory for the accurate determination of anti-SARS-CoV-2 antibodies for diagnosis, serosurveillance, and vaccine trials.

Point-of-Care Diagnostics of COVID-19: From Current Work to Future Perspectives

Coronaviruses have received global concern since 2003, when an outbreak caused by SARS-CoV emerged in China. Later on, in 2012, the Middle-East respiratory syndrome spread in Saudi Arabia, caused by MERS-CoV. Currently, the global crisis is caused by the pandemic SARS-CoV-2, which belongs to the same lineage of SARS-CoV. In response to the urgent need of diagnostic tools, several lab-based and biosensing techniques have been proposed so far. Five main areas have been individuated and discussed in terms of their strengths and weaknesses. The cell-culture detection and the microneutralization tests are still considered highly reliable methods. The genetic screening, featuring the well-established Real-time polymerase chain reaction (RT-PCR), represents the gold standard for virus detection in nasopharyngeal swabs. On the other side, immunoassays were developed, either by screening/antigen recognition of IgM/IgG or by detecting the whole virus, in blood and sera. Next, proteomic mass-spectrometry (MS)-based methodologies have also been proposed for the analysis of swab samples. Finally, virus-biosensing devices were efficiently designed. Both electrochemical immunosensors and eye-based technologies have been described, showing detection times lower than 10 min after swab introduction. Alternative to swab-based techniques, lateral flow point-of-care immunoassays are already commercially available for the analysis of blood samples. Such biosensing devices hold the advantage of being portable for on-site testing in hospitals, airports, and hotspots, virtually without any sample treatment or complicated lab precautions.

Rapid and Sensitive Detection of anti-SARS-CoV-2 IgG, Using Lanthanide-Doped Nanoparticles-Based Lateral Flow Immunoassay

The outbreak of 2019 coronavirus disease (COVID-19) has been a challenge for hospital laboratories because of the huge number of samples that must be tested for the presence of the causative pathogen, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Simple and rapid immunodiagnostic methods are urgently needed to identify positive cases. Here we report the development of a rapid and sensitive lateral flow immunoassay (LFIA) that uses lanthanide-doped polysterene nanoparticles (LNPs) to detect anti-SARV-CoV-2 IgG in human serum. A recombinant nucleocapsid phosphoprotein of SARS-CoV-2 was dispensed onto a nitrocellulose membrane to capture specific IgG. Mouse anti-human IgG antibody was labeled with self-assembled LNPs that served as a fluorescent reporter. A 100-μL aliquot of serum samples (1:1000 dilution) was used for this assay and the whole detection process took 10 min. The results of the validation experiment met the requirements for clinical diagnostic reagents. A value of 0.0666 was defined as the cutoff value by assaying 51 normal samples. We tested 7 samples that were positive by reverse-transcription (RT-)PCR and 12 that were negative but clinically suspicious for the presence of anti-SARS-CoV-2 IgG. One of the negative samples was determined to be SARS-CoV-2 IgG positive, while the results for the other samples were consistent with those obtained by RT-PCR. Thus, this assay can achieve rapid and sensitive detection of anti-SARS-CoV-2 IgG in human serum and allow positive identification in suspicious cases; it can also be useful for monitoring the progression COVID-19 and evaluating patients' response to treatment.

Rapid and Sensitive Detection of anti-SARS-CoV-2 IgG, Using Lanthanide-Doped Nanoparticles-Based Lateral Flow Immunoassay

The outbreak of 2019 coronavirus disease (COVID-19) has been a challenge for hospital laboratories because of the huge number of samples that must be tested for the presence of the causative pathogen, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Simple and rapid immunodiagnostic methods are urgently needed to identify positive cases. Here we report the development of a rapid and sensitive lateral flow immunoassay (LFIA) that uses lanthanide-doped polysterene nanoparticles (LNPs) to detect anti-SARV-CoV-2 IgG in human serum. A recombinant nucleocapsid phosphoprotein of SARS-CoV-2 was dispensed onto a nitrocellulose membrane to capture specific IgG. Mouse anti-human IgG antibody was labeled with self-assembled LNPs that served as a fluorescent reporter. A 100-μL aliquot of serum samples (1:1000 dilution) was used for this assay and the whole detection process took 10 min. The results of the validation experiment met the requirements for clinical diagnostic reagents. A value of 0.0666 was defined as the cutoff value by assaying 51 normal samples. We tested 7 samples that were positive by reverse-transcription (RT-)PCR and 12 that were negative but clinically suspicious for the presence of anti-SARS-CoV-2 IgG. One of the negative samples was determined to be SARS-CoV-2 IgG positive, while the results for the other samples were consistent with those obtained by RT-PCR. Thus, this assay can achieve rapid and sensitive detection of anti-SARS-CoV-2 IgG in human serum and allow positive identification in suspicious cases; it can also be useful for monitoring the progression COVID-19 and evaluating patients' response to treatment.

Validation of a SARS-CoV-2 spike protein ELISA for use in contact investigations and serosurveillance

Since emergence of SARS-CoV-2 in late 2019, there has been a critical need to understand prevalence, transmission patterns, to calculate the burden of disease and case fatality rates. Molecular diagnostics, the gold standard for identifying viremic cases, are not ideal for determining true case counts and rates of asymptomatic infection. Serological detection of SARS-CoV-2 specific antibodies can contribute to filling these knowledge gaps. In this study, we describe optimization and validation of a SARS-CoV-2-specific-enzyme linked immunosorbent assay (ELISA) using the prefusion-stabilized form of the spike protein [1]. We performed receiver operator characteristic (ROC) analyses to define the specificities and sensitivities of the optimized assay and examined cross reactivity with immune sera from persons confirmed tohave had infections with other coronaviruses. These assays will be used to perform contact investigations and to conduct large-scale, cross sectional surveillance to define disease burden in the population.

A systematic review of antibody mediated immunity to coronaviruses: antibody kinetics, correlates of protection, and association of antibody responses with severity of disease

The duration and nature of immunity generated in response to SARS-CoV-2 infection is unknown. Many public health responses and modeled scenarios for COVID-19 outbreaks caused by SARSCoV-2 assume that infection results in an immune response that protects individuals from future infections or illness for some amount of time. The timescale of protection is a critical determinant of the future impact of the pathogen. The presence or absence of protective immunity due to infection or vaccination (when available) will affect future transmission and illness severity. The dynamics of immunity and nature of protection are relevant to discussions surrounding therapeutic use of convalescent sera as well as efforts to identify individuals with protective immunity. Here, we review the scientific literature on antibody immunity to coronaviruses, including SARS-CoV-2 as well as the related SARS-CoV-1, MERS-CoV and human endemic coronaviruses (HCoVs). We reviewed 1281 abstracts and identified 322 manuscripts relevant to 5 areas of focus: 1) antibody kinetics, 2) correlates of protection, 3) immunopathogenesis, 4) antigenic diversity and cross-reactivity, and 5) population seroprevalence. While studies of SARS-CoV-2 are necessary to determine immune responses to it, evidence from other coronaviruses can provide clues and guide future research.

A novel luciferase immunosorbent assay performs better than a commercial enzyme-linked immunosorbent assay to detect MERS-CoV specific IgG in humans and animals

The Middle East respiratory syndrome (MERS) is a lethal zoonosis caused by MERS coronavirus (MERS-CoV) and poses a significant threat to public health worldwide. Therefore, a rapid, sensitive, and specific serologic test for detecting anti-MERS-CoV antibodies in both humans and animals is urgently needed for the successful management of this illness. Here, we evaluated various novel luciferase immunosorbent assays (LISA) based on nucleocapsid protein (NP) as well as fragments derived from spike protein (S) including subunit 1 (S1), N terminal domain (NTD), receptor-binding domain (RBD) and subunit 2 (S2) of S for the detection of MERS-CoV-specific IgG. Fusion proteins, including nanoluciferase (NLuc) and various fragments derived from the NP or S protein of MERS-CoV, were expressed in human embryonic kidney 293 T cells. LISAs that detected anti-MERS-CoV IgG were further developed using cell lysates expressing various fusion proteins. Panels of human or animal samples infected with MERS-CoV were used to analyze the sensitivity and specificity of various LISAs in reference to a MERS-CoV RT-PCR, commercial S1-based ELISA, and pseudovirus particle neutralization test (ppNT). Our results showed that the S1-, RBD-, and NP-LISAs were more sensitive than the NTD- and S2-LISAs for the detection of anti-MERS-CoV IgG. Furthermore, the S1-, RBD-, and NP-LISAs were more sensitive (by at least 16-fold) than the commercially available S1-ELISA. Moreover, the S1-, RBD-, and NP-LISA specifically recognized anti-MERS-CoV IgG and did not cross-react with samples derived from other human CoV (OC43, 229E, HKU1, NL63)-infected patients. More importantly, these LISAs proved their applicability and reliability for detecting anti-MERS-CoV IgG in samples from camels, monkeys, and mice, among which the RBD-LISA exhibited excellent performance. The results of this study suggest that the novel MERS-CoV RBD- and S1- LISAs are highly effective platforms for the rapid and sensitive detection of anti-MERS-CoV IgG in human and animal samples. These assays have the potential to be used as serologic tests for the management and control of MERS-CoV infection.

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Scientific question

This study evaluated novel luciferase immunosorbent assays (LISAs) based on nucleocapsid protein (NP) as well as fragments derived from spike protein (S) for detection of MERS-CoV-specific IgG in humans and animals.

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Evidence before this study

Enzyme-linked immunosorbent assay (ELISA), microneutralization (MN), immunofluorescence assay (IFA), and pseudovirus particle neutralization test (ppNT) have been performed to detect serum antibodies against MERS-CoV. There remains a need to develop novel serological assays independent of protein purification, special secondary antibody, virus cultivation and Biosafety Level 3 (BSL-3) laboratory.

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New findings

In this study, novel LISAs based on the MERS-CoV S fragments and NP were developed. Human and animal samples infected with MERS-CoV were measured by the newly developed LISAs as well as reference methods including commercial S1-ELISA and ppNT. The results showed that the S1-, RBD-, and NP-LISAs were able to specifically distinguish MERS-CoV-infected samples from samples infected by other HCoV as consistent as the reference methods. Comparing with the commercially available S1-ELISA, the S1- and RBD-LISAs were 64-folds more sensitive. Moreover, the applicability and reliability of the LISAs were verified by detecting anti-MERS-CoV IgG in samples from camels, monkeys, and mice. The RBD-LISA exhibited superior sensitivity and specificity.

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Significance of the study

The novel MERS-CoV RBD- and S1-LISAs were developed independent of protein purification and special secondary antibody, and showed super specificity and efficiency for the detection of anti-MERS-CoV IgG in human and animal samples. These assays are recommended for serological diagnosis of MERS-CoV infection in the investigation of epidemic characteristic, origin tracing and vaccine study of MERS-CoV, they would contribute to the scientific control and prevention of MERS.