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

Determinants of Systemic SARS-CoV-2-Specific Antibody Responses to Infection and to Vaccination: A Secondary Analysis of Randomised Controlled Trial Data

SARS-CoV-2 infections elicit antibodies against the viral spike (S) and nucleocapsid (N) proteins; COVID-19 vaccines against the S-protein only. The BCG-Corona trial, initiated in March 2020 in SARS-CoV-2-naïve Dutch healthcare workers, captured several epidemic peaks and the introduction of COVID-19 vaccines during the one-year follow-up. We assessed determinants of systemic anti-S1 and anti-N immunoglobulin type G (IgG) responses using trial data. Participants were randomised to BCG or placebo vaccination, reported daily symptoms, SARS-CoV-2 test results, and COVID-19 vaccinations, and donated blood for SARS-CoV-2 serology at two time points. In the 970 participants, anti-S1 geometric mean antibody concentrations (GMCs) were much higher than anti-N GMCs. Anti-S1 GMCs significantly increased with increasing number of immune events (SARS-CoV-2 infection or COVID-19 vaccination): 104.7 international units (IU)/mL, 955.0 IU/mL, and 2290.9 IU/mL for one, two, and three immune events, respectively (p < 0.001). In adjusted multivariable linear regression models, anti-S1 and anti-N log10 concentrations were significantly associated with infection severity, and anti-S1 log10 concentration with COVID-19 vaccine type/dose. In univariable models, anti-N log10 concentration was also significantly associated with acute infection duration, and severity and duration of individual symptoms. Antibody concentrations were not associated with long COVID or long-term loss of smell/taste.

Boosting the immunogenicity of the CoronaVac SARS-CoV-2 inactivated vaccine with Huoxiang Suling Shuanghua Decoction: a randomized, double-blind, placebo-controlled study

Introduction

In light of the public health burden of the COVID-19 pandemic, boosting the safety and immunogenicity of COVID-19 vaccines is of great concern. Numerous Traditional Chinese medicine (TCM) preparations have shown to beneficially modulate immunity. Based on pilot experiments in mice that showed that supplementation with Huoxiang Suling Shuanghua Decoction (HSSD) significantly enhances serum anti-RBD IgG titers after inoculation with recombinant SARS-CoV-2 S-RBD protein, we conducted this randomized, double-blind, placebo-controlled clinical trial aimed to evaluate the potential immunogenicity boosting effect of oral HSSD after a third homologous immunization with Sinovac's CoronaVac SARS-CoV-2 (CVS) inactivated vaccine.

Methods

A total of 70 participants were randomly assigned (1:1 ratio) to receive a third dose of CVS vaccination and either oral placebo or oral HSSD for 7 days. Safety aspects were assessed by recording local and systemic adverse events, and by blood and urine biochemistry and liver and kidney function tests. Main outcomes evaluated included serum anti-RBD IgG titer, T lymphocyte subsets, serum IgG and IgM levels, complement components (C3 and C4), and serum cytokines (IL-6 and IFN-γ). In addition, metabolomics technology was used to analyze differential metabolite expression after supplementation with HSSD.

Results

Following a third CVS vaccination, significantly increased serum anti-RBD IgG titer, reduced serum IL-6 levels, increased serum IgG, IgM, and C3 and C4 levels, and improved cellular immunity, evidenced by reduce balance deviations in the distribution of lymphocyte subsets, was observed in the HSSD group compared with the placebo group. No serious adverse events were recorded in either group. Serum metabolomics results suggested that the mechanisms by which HSSD boosted the immunogenicity of the CVS vaccine are related to differential regulation of purine metabolism, vitamin B6 metabolism, folate biosynthesis, arginine and proline metabolism, and steroid hormone biosynthesis.

Conclusion

Oral HSSD boosts the immunogenicity of the CVS vaccine in young and adult individuals. This trial provides clinical reference for evaluation of TCM immunomodulators to improve the immune response to COVID-19 vaccines.

Approaches to evaluate the specific immune responses to SARS-CoV-2

The SARS-CoV-2 pandemic has a huge impact on public health and global economy, meaning an enormous scientific, political, and social challenge. Studying how infection or vaccination triggers both cellular and humoral responses is essential to know the grade and length of protection generated in the population. Nowadays, scientists and authorities around the world are increasingly concerned about the arrival of new variants, which have a greater spread, due to the high mutation rate of this virus. The aim of this review is to summarize the different techniques available for the study of the immune responses after exposure or vaccination against SARS-CoV-2, showing their advantages and limitations, and proposing suitable combinations of different techniques to achieve extensive information in these studies. We wish that the information provided here will helps other scientists in their studies of the immune response against SARS-CoV-2 after vaccination with new vaccine candidates or infection with upcoming variants.

Immunological responses and adverse reactions of the heterologous second booster dose of BNT162b2 after two-dose CoronaVac for COVID-19 vaccination in healthcare workers of Faculty of Medicine, Naresuan University

BACKGROUND

The first COVID-19 vaccination campaign in Thailand began in April 2020, with healthcare workers receiving two doses of inactivated COVID-19 vaccine (CoronaVac). However, the emergence of the delta and omicron variants raised concerns about vaccine effectiveness. The Thai Ministry of Public Health provided the first booster dose (third dose) and second booster dose (fourth dose) of the mRNA vaccine (BNT162b2) for healthcare workers. This study investigated the immunity and adverse reactions elicited by a heterologous second booster dose of BNT162b2 after a two-dose CoronaVac vaccination for COVID-19 in healthcare workers of the Faculty of Medicine, Naresuan University.

METHODS

IgG titres against the SARS-CoV-2-spike protein were measured four and 24 weeks after the second booster dose of BNT162b2 in the study participants. Adverse reactions were recorded during the first three days, four weeks and 24 weeks after the second booster dose of BNT162b2.

RESULTS

IgG against the SARS-CoV-2-spike protein was positive (>10 U/ml) in 246 of 247 participants (99.6 %) at both four and 24 weeks after the second booster dose of BNT162b2. The median specific IgG titres at four and 24 weeks after the second booster dose of BNT162b2 were 299 U/ml (min: 2, max: 29,161) and 104 U/ml (min: 1, max: 17,920), respectively. The median IgG level declined significantly 24 weeks after the second booster dose of the BNT162b2 vaccine. Of the 247 participants, 179 (72.5 %) experienced adverse reactions in the first three days after the second booster dose of BNT162b2. Myalgia, fever, headache, injection site pain and fatigue were the most common adverse reactions.

CONCLUSION

This study demonstrated that a heterologous second booster dose of BNT162b2 after two doses of CoronaVac induced elevated IgG against the SARS-CoV-2-spike protein and caused minor adverse reactions in healthcare workers of the Faculty of Medicine, Naresuan University. This study was registered as Thailand Clinical Trials No. TCTR20221112001.

Rapid, early, and potent Spike-directed IgG, IgM, and IgA distinguish asymptomatic from mildly symptomatic COVID-19 in Uganda, with IgG persisting for 28 months

Introduction

Understanding how spike (S)-, nucleoprotein (N)-, and RBD-directed antibody responses evolved in mild and asymptomatic COVID-19 in Africa and their interactions with SARS-CoV-2 might inform development of targeted treatments and vaccines.

Methods

Here, we used a validated indirect in-house ELISA to characterise development and persistence of S- and N-directed IgG, IgM, and IgA antibody responses for 2430 SARS-CoV-2 rt-PCR-diagnosed Ugandan specimens from 320 mild and asymptomatic COVID-19 cases, 50 uninfected contacts, and 54 uninfected non-contacts collected weekly for one month, then monthly for 28 months.

Results

During acute infection, asymptomatic patients mounted a faster and more robust spike-directed IgG, IgM, and IgA response than those with mild symptoms (Wilcoxon rank test, p-values 0.046, 0.053, and 0.057); this was more pronounced in males than females. Spike IgG antibodies peaked between 25 and 37 days (86.46; IQR 29.47-242.56 BAU/ml), were significantly higher and more durable than N- and RBD IgG antibodies and lasted for 28 months. Anti-spike seroconversion rates consistently exceeded RBD and nucleoprotein rates. Spike- and RBD-directed IgG antibodies were positively correlated until 14 months (Spearman's rank correlation test, p-values 0.0001 to 0.05), although RBD diminished faster. Significant anti-spike immunity persisted without RBD. 64% and 59% of PCR-negative, non-infected non-contacts and suspects, exhibited baseline SARS-CoV-2 N-IgM serological cross-reactivity, suggesting undetected exposure or abortive infection. N-IgG levels waned after 787 days, while N-IgM levels remained undetectable throughout.

Discussion

Lower N-IgG seroconversion rates and the absence of N-IgM indicate that these markers substantially underestimate the prior exposure rates. Our findings provide insights into the development of S-directed antibody responses in mild and asymptomatic infections, with varying degrees of symptoms eliciting distinct immune responses, suggesting distinct pathogenic pathways. These longer-lasting data inform vaccine design, boosting strategies, and surveillance efforts in this and comparable settings.

Portable high-throughput multimodal immunoassay platform for rapid on-site COVID-19 diagnostics

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as a causal agent of Coronavirus Disease 2019 (COVID-19) has led to the global pandemic. Though the real-time reverse transcription polymerase chain reaction (RT-PCR) acting as a gold-standard method has been widely used for COVID-19 diagnostics, it can hardly support rapid on-site applications or monitor the stage of disease development as well as to identify the infection and immune status of rehabilitation patients. To suit rapid on-site COVID-19 diagnostics under various application scenarios with an all-in-one device and simple detection reagents, we propose a high-throughput multimodal immunoassay platform with fluorescent, colorimetric, and chemiluminescent immunoassays on the same portable device and a multimodal reporter probe using quantum dot (QD) microspheres modified with horseradish peroxidase (HRP) coupled with goat anti-human IgG. The recombinant nucleocapsid protein fixed on a 96-well plate works as the capture probe. In the condition with the target under detection, both reporter and capture probes can be bound by such target. When illuminated by excitation light, fluorescence signals from QD microspheres can be collected for target quantification often at a fast speed. Additionally, when pursuing simple detection without using any sensing devices, HRP-catalyzed TMB colorimetric immunoassay is employed; and when pursuing highly sensitive detection, HRP-catalyzed luminol chemiluminescent immunoassay is established. Verified by the anti-SARS-CoV-2 N humanized antibody, the sensitivities of colorimetric, fluorescent, and chemiluminescent immunoassays are respectively 20, 80, and 640 times more sensitive than that of the lateral flow colloidal gold immunoassay strip. Additionally, such a platform can simultaneously detect multiple samples at the same time thus supporting high-throughput sensing; and all these detecting operations can be implemented on-site within 50 min relying on field-operable processing and field-portable devices. Such a high-throughput multimodal immunoassay platform can provide a new all-in-one solution for rapid on-site diagnostics of COVID-19 for different detecting purposes.

Strong Neutralizing Antibody Responses to SARS-CoV-2 Variants Following a Single Vaccine Dose in Subjects With Previous SARS-CoV-2 Infection

BACKGROUND

Previous severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection primes the immune system; thus individuals who have recovered from infection have enhanced immune responses to subsequent vaccination (hybrid immunity). However, it remains unclear how well hybrid immunity induced by severe or mild infection can cross-neutralize emerging variants. We aimed to compare the strength and breadth of antibody responses in vaccinated recovered and uninfected subjects.

METHODS

We measured spike-specific immunoglobulin (Ig)G and neutralizing antibodies (NAbs) from vaccinated subjects including 320 with hybrid immunity and 20 without previous infection. From 29 subjects with a previous severe or mild infection, we also measured NAb responses against Alpha (B.1.1.7), Beta (B.1.351), Delta (B.1.617.2), and Omicron (B.1.1.529/BA.1) variants following vaccination.

RESULTS

A single vaccine dose induced 2-fold higher anti-spike IgG concentrations and up to 4-fold higher neutralizing potency of antibodies in subjects with a previous infection compared with vaccinated subjects without a previous infection. Hybrid immunity was more enhanced after a severe than a mild infection, with sequentially decreasing NAb titers against Alpha, Beta, Delta, and Omicron variants. We found similar IgG concentrations in subjects with a previous infection after 1 or 2 vaccine doses.

CONCLUSIONS

Hybrid immunity induced strong IgG responses, particularly after severe infection. However, the NAb titers were low against heterologous variants, especially against Omicron.

Impaired immunity and high attack rates caused by SARS-CoV-2 variants among vaccinated long-term care facility residents

INTRODUCTION

Long-term care facilities (LTCF) residents are at high risk for severe coronavirus disease 2019 (COVID-19), and therefore, COVID-19 vaccinations were prioritized for residents and personnel in Finland at the beginning of 2021.

METHODS

We investigated COVID-19 outbreaks in two LTCFs, where residents were once or twice vaccinated. After the outbreaks we measured immunoglobulin G (IgG) antibodies to severe acute respiratory syndrome coronavirus 2 spike glycoprotein, neutralizing antibody (NAb) titers, and cell-mediated immunity markers from residents and healthcare workers (HCWs).

RESULTS

In LTFC-1, the outbreak was caused by an Alpha variant (B.1.1.7) and the attack rate (AR) among once vaccinated residents was 23%. In LTCF-2 the outbreak was caused by a Beta variant (B.1.351). Its AR was 47% although all residents had received their second dose 1 month before the outbreak. We observed that vaccination had induced lower IgG concentrations, NAb titers and cell-mediated immune responses in residents compared to HCWs. Only 1/8 residents had NAb to the Beta variant after two vaccine doses.

CONCLUSIONS

The vaccinated elderly remain susceptible to breakthrough infections caused by Alpha and Beta variants. The weaker vaccine response in the elderly needs to be addressed in vaccination protocols, while new variants capable of evading vaccine-induced immunity continue to emerge.

High secondary attack rate and persistence of SARS-CoV-2 antibodies in household transmission study participants, Finland 2020–2021

Background

Household transmission studies offer the opportunity to assess both secondary attack rate (SAR) and persistence of SARS-CoV-2 antibodies over time.

Methods

In Spring 2020, we invited confirmed COVID-19 cases and their household members to four visits, where we collected nasopharyngeal and serum samples over 28 days after index case onset. We calculated SAR based on the presence of SARS-CoV-2 neutralizing antibodies (NAb) and assessed the persistence of NAb and IgG antibodies (Ab) against SARS-CoV-2 spike glycoprotein and nucleoprotein.

Results

SAR was 45% (39/87), including 35 symptomatic secondary cases. During the initial 28-day follow-up, 62% (80/129) of participants developed NAb. Of those that seroconverted, 90% (63/70), 85% (63/74), and 78% (45/58) still had NAb to early B-lineage SARS-CoV-2 3, 6, and 12 months after the onset of the index case. Anti-spike IgG Ab persisted in 100% (69/69), 97% (72/74), and 93% (55/59) of seroconverted participants after 3, 6, and 12 months, while anti-nucleoprotein IgG Ab levels waned faster, persisting in 99% (68/69), 78% (58/74), and 55% (39/71) of participants, respectively.

Conclusion

Following detection of a COVID-19 case in a household, other members had a high risk of becoming infected. NAb to early B-lineage SARS-CoV-2 persisted for at least a year in most cases.

Harmonization of Multiple SARS-CoV-2 Reference Materials Using the WHO IS (NIBSC 20/136): Results and Implications

Background

There is an urgent need for harmonization between severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serology platforms and assays prior to defining appropriate correlates of protection and as well inform the development of new rapid diagnostic tests that can be used for serosurveillance as new variants of concern (VOC) emerge. We compared multiple SARS-CoV-2 serology reference materials to the WHO International Standard (WHO IS) to determine their utility as secondary standards, using an international network of laboratories with high-throughput quantitative serology assays. This enabled the comparison of quantitative results between multiple serology platforms.

Methods

Between April and December 2020, 13 well-characterized and validated SARS-CoV-2 serology reference materials were recruited from six different providers to qualify as secondary standards to the WHO IS. All the samples were tested in parallel with the National Institute for Biological Standards and Control (NIBSC) 20/136 and parallel-line assays were used to calculate the relevant potency and binding antibody units.

Results

All the samples saw varying levels of concordance between diagnostic methods at specific antigen–antibody combinations. Seven of the 12 candidate materials had high concordance for the spike-immunoglobulin G (IgG) analyte [percent coefficient of variation (%CV) between 5 and 44%].

Conclusion

Despite some concordance between laboratories, qualification of secondary materials to the WHO IS using arbitrary international units or binding antibody units per milliliter (BAU/ml) does not provide any benefit to the reference materials overall, due to the lack of consistent agreeable international unit (IU) or BAU/ml conversions between laboratories. Secondary standards should be qualified to well-characterized reference materials, such as the WHO IS, using serology assays that are similar to the ones used for the original characterization of the WHO IS.

Neutralizing antibodies to SARS-CoV-2 Omicron variant after third mRNA vaccination in health care workers and elderly subjects

The emergence of SARS-CoV-2 Omicron variant (B.1.1.529) with major spike protein mutations has raised concern over potential neutralization escape and breakthrough infections among vaccinated and previously SARS-CoV-2-infected subjects. We measured cross-protective antibodies against variants in health care workers (HCW, n = 20) and nursing home residents (n = 9) from samples collected at 1-2 months, following the booster (3rd) dose. We also assessed the antibody responses in subjects infected before the Omicron era (n = 38) with subsequent administration of a single mRNA vaccine dose. Following booster vaccination, HCWs had high IgG antibody concentrations to the spike protein and neutralizing antibodies (NAb) were detectable against all variants. IgG concentrations among the elderly remained lower, and some lacked NAbs against the Beta and Omicron variants. NAb titers were significantly reduced against Delta, Beta, and Omicron compared to WT virus regardless of age. Vaccination induced high IgG concentrations and variable titers of cross-reactive NAbs in previously infected subjects, whereas NAb titers against Omicron were barely detectable 1 month postinfection. High IgG concentrations with cross-protective neutralizing activity were detected after three Coronavirus Disease 2019 (COVID-19) vaccine doses in HCWs. However, lower NAb titers seen in the frail elderly suggest inadequate protection against Omicron breakthrough infections, yet protection against severe COVID-19 is expected.

Limited Variation between SARS-CoV-2-Infected Individuals in Domain Specificity and Relative Potency of the Antibody Response against the Spike Glycoprotein

The spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is arranged as a trimer on the virus surface, composed of three S1 and three S2 subunits. Infected and vaccinated individuals generate antibodies against spike, which can neutralize the virus. Most antibodies target the receptor-binding domain (RBD) and N-terminal domain (NTD) of S1; however, antibodies against other regions of spike have also been isolated. The interhost variability in domain specificity and relative neutralization efficacy of the antibodies is still poorly characterized. To this end, we tested serum and plasma samples collected from 85 coronavirus disease 2019 (COVID-19) convalescent subjects. Samples were analyzed using seven immunoassays that employ different domains, subunits, and oligomeric forms of spike to capture the antibodies. Samples were also tested for their neutralization of pseudovirus containing SARS-CoV-2 spike and of replication-competent SARS-CoV-2. While the total amount of anti-spike antibodies produced varied among convalescent subjects, we observed an unexpectedly fixed ratio of RBD- to NTD-targeting antibodies. The relative potency of the response (defined as the measured neutralization efficacy relative to the total level of spike-targeting antibodies) also exhibited limited variation between subjects and was not associated with the overall amount of antispike antibodies produced. These studies suggest that host-to-host variation in the polyclonal response elicited against SARS-CoV-2 spike in early pandemic subjects is primarily limited to the quantity of antibodies generated rather than their domain specificity or relative neutralization potency. IMPORTANCE Infection by SARS-CoV-2 elicits antibodies against various domains of the spike protein, including the RBD and NTD of subunit S1 and against subunit S2. The antibody responses of different infected individuals exhibit different efficacies to inactivate (neutralize) the virus. Here, we show that the observed variation in the neutralizing activity of the antibody responses in COVID-19 convalescent subjects is caused by differences in the amounts of antibodies rather than their recognition properties or the potency of their antiviral activity. These findings suggest that COVID-19 vaccine strategies that focus on enhancing the overall level of the antibodies will likely elicit a more uniformly efficacious protective response.

Development of Serological Assays and Seroprevalence Studies of the New Coronavirus 2019 (COVID-19): Reports from Saudi Arabia

Serological assays are valuable tools for tracking COVID-19 spread, estimation of herd immunity, and evaluation of vaccine effectiveness. Several reports from Saudi Arabia describe optimized in-house protocols that enable detection of SARS-CoV-2 specific antibodies and measurement of their neutralizing activity. Notably, there were variations in the approaches utilized to develop and validate these immunoassays in term of sample size, validation methodologies, and statistical analyses. The developed enzyme-linked immunoassays (ELISAs) were based on the viral full-length spike (S), S1 subunit, and nucleocapsid (NP), and enabled detection of IgM and/or IgG. ELISAs were evaluated and validated against a microneutralization assay utilizing a local SARS-CoV-2 clinical isolate, FDA-approved commercially available immunoassays, and/or real-time polymerase chain reaction (RT-PCR). Overall, the performance of the described assays was high, reaching up to 100% sensitivity and 98.9% specificity with no cross-reactivity with other coronaviruses. In-house immunoassays, along with commercially available kits, were subsequently applied in a number of sero-epidemiological studies aiming to estimate sero-positivity status among local populations including healthcare workers, COVID-19 patients, non-COVID-19 patients, and healthy blood donors. The reported seroprevalence rates differed widely among these studies, ranging from 0.00% to 32.2%. These variations are probably due to study period, targeted population, sample size, and performance of the immunoassays utilized. Indeed, lack of sero-positive cases were reported among healthy blood donors during the lockdown, while the highest rates were reported when the number of COVID-19 cases peaked in the country, particularly among healthcare workers working in referral hospitals and quarantine sites. In this review, we aim to (1) provide a critical discussion about the developed in-house immunoassays, and (2) summarize key findings of the sero-epidemiological studies and highlight strengths and weaknesses of each study.

Persistence of neutralizing antibodies a year after SARS-CoV-2 infection in humans

Most subjects develop antibodies to SARS-CoV-2 following infection. In order to estimate the duration of immunity induced by SARS-CoV-2 it is important to understand for how long antibodies persist after infection in humans. Here, we assessed the persistence of serum antibodies following WT SARS-CoV-2 infection at 8 and 13 months after diagnosis in 367 individuals. The SARS-CoV-2 spike IgG (S-IgG) and nucleoprotein IgG (N-IgG) concentrations and the proportion of subjects with neutralizing antibodies (NAb) were assessed. Moreover, the NAb titers among a smaller subset of participants (n = 78) against a WT virus (B) and variants of concern (VOCs): Alpha (B.1.1.7), Beta (B.1.351), and Delta (B.1.617.2) were determined. We found that NAb against the WT virus persisted in 89% and S-IgG in 97% of subjects for at least 13 months after infection. Only 36% had N-IgG by 13 months. The mean S-IgG concentrations declined from 8 to 13 months by less than one third; N-IgG concentrations declined by two-thirds. Subjects with severe infection had markedly higher IgG and NAb levels and are expected to remain seropositive for longer. Significantly lower NAb titers against the variants compared to the WT virus, especially after a mild disease, suggests reduced protection against VOCs.