mRNA vaccination boosts cross-variant neutralizing antibodies elicited by SARS-CoV-2 infection

The comprehensive insights into the B-cells-mediated immune response against COVID-19 infection amid the ongoing evolution of SARS-CoV-2

The antibody-mediated immune response is crucial for the development of protective immunity against SARS-CoV-2, the virus responsible for the COVID-19 pandemic. Understanding the interaction between SARS-CoV-2 and the immune system is critical because new variants emerge as a result of the virus's ongoing evolution. Understanding the function of B cells in the SARS-CoV-2 infection process is critical for developing effective and long-lasting vaccines against this virus. Triggered by the innate immune response, B cells transform into memory B cells (MBCs). It is fascinating to observe how MBCs provide enduring immune defence, not only eradicating the infection but also safeguarding against future reinfection. If there is a lack of B cell activation or if the B cells are not functioning properly, it can lead to a serious manifestation of the disease and make immunisation less effective. Individuals with disruptions in the B cells have shown increased production of cytokines and chemokines, resulting in a poor prognosis for the disease. Therefore, we have developed an updated review article to gain insight into the involvement of B cells in SARS-CoV-2 infection. The discussion has covered the generation, functioning, and dynamics of neutralising antibodies (nAbs). Furthermore, we have emphasised immunotherapeutics that rely on nAbs.

Persistence and decay of neutralizing antibody responses elicited by SARS-CoV-2 infection and hybrid immunity in a Canadian cohort

A major challenge with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), has been assessing the intensity, dynamics, and determinants of the antibody responses after infection and/or vaccination. Therefore, we aimed to characterize the longitudinal dynamics of the antibody responses among naturally infected individuals and individuals who achieved hybrid immunity in a large Canadian cohort. We demonstrate that anti-Spike IgGs and neutralizing antibody dynamics vary greatly among individuals with COVID-19, in peak antibody levels, rate of waning, and longevity of the antibody response. Additionally, we found an association between robust antibody responses and individuals with severe COVID-19 clinical symptoms during the first-month post-symptom onset. For individuals who achieved hybrid immunity, a robust increase in anti-S1 IgGs and neutralizing antibodies followed the first vaccination dose; however, there was a minimal increase in the anti-S1 IgGs and neutralizing antibody titers after administration of the second dose of the vaccine. Furthermore, neutralizing antibodies elicited by the wild-type virus alone were largely ineffective against emerging variants of concern in our natural infection-only cohort, in contrast to a much broader and more robust neutralization profile observed in individuals who achieved hybrid immunity. Our findings emphasize the need for global SARS-CoV-2 vaccination efforts to further sustain protective immune responses required to minimize viral spread and disease severity in the population. As SARS-CoV-2 variants continue to emerge, understanding the interplay between previous infections, vaccine durability, and virus evolution will be critical for guiding ongoing vaccination strategies.

IMPORTANCE

A major challenge with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), has been assessing the intensity, dynamics, and determinants of the antibody response after infection and/or vaccination. Our paper addresses this in a large Canadian cohort with antibody responses that were generated by natural infection as well as vaccine in some persons studied.

Nucleocapsid-directed antibody testing is unsuitable to estimate hybrid immunity against SARS-CoV-2, a longitudinal cross-border study in the Meuse-Rhine Euroregion

INTRODUCTION

Understanding immunity from previous natural SARS-CoV-2 infection is important for booster vaccination strategies. A longitudinal study conducted in 2021 within the Meuse-Rhine Euroregion, bordering the Netherlands, Belgium, and Germany, aimed to assess seroprevalence of spike-directed (anti-S) and nucleocapsid-directed (anti-N) antibodies to demonstrate immunity as a result of both vaccination and natural infection (hybrid immunity), and to evaluate the dynamics of the anti-N response.

MATERIALS AND METHODS

Questionnaires and self-finger-prick blood samples from 3110 participants were collected at two time points: weeks 22-29 (June-July, round 1) and weeks 40-45 (October-November, round 2) of 2021. Individuals with anti-S antibodies were additionally tested for anti-N antibodies.

RESULTS

In total, 4366 samples tested positive for anti-S; n = 1291 for round 1 and n = 3075 for round 2. Of these, 10.1 % of Dutch (32/316), 3.1 % of Belgian (9/294), and 2.8 % of German participants (13/466) were anti-N positive in round 1 (p < 0.001). In round 2, this was 4.6 % (69/1510), 3.3 % (20/607), and 1.5 % (14/912), respectively (p < 0.001). In 45.1 % (23/51) of anti-N positive participants in round 1, the result reversed to negative in round 2. In 42.1 % (16/38) of anti-N positive participants with a self-reported positive PCR result, anti-N reversed to negative in round 2.

CONCLUSION

Variations in anti-N seroprevalence across EMR countries may reflect differences in vaccination campaign enrollment. Over 40 % of participants experienced seroreversion of anti-N within six months, indicating anti-N testing is unsuitable for diagnosing past infection or estimating hybrid immunity within a population. However, anti-N testing may be used as a proxy for increased circulation of SARS-CoV-2 in a population.

RBD-depleted SARS-CoV-2 spike generates protective immunity in cynomolgus macaques

The SARS-CoV-2 pandemic revealed the rapid evolution of circulating strains. This led to new variants carrying mostly mutations within the receptor binding domain, which is immunodominant upon immunization and infection. In order to steer the immune response away from RBD epitopes to more conserved domains, we generated S glycoprotein trimers without RBD and stabilized them by formaldehyde cross-linking. The cryoEM structure demonstrated that SΔRBD folds into the native prefusion conformation, stabilized by one specific cross-link between S2 protomers. SΔRBD was coated onto lipid vesicles, to produce synthetic virus-like particles, SΔRBD-LV, which were utilized in a heterologous prime-boost strategy. Immunization of cynomolgus macaques either three times with the mRNA Comirnaty vaccine or two times followed by SΔRBD-LV showed that the SΔRBD-LV boost induced similar antibody titers and neutralization of different variants, including omicron. Upon challenge with omicron XBB.3, both the Comirnaty only and Comirnaty/SΔRBD-LV vaccination schemes conferred similar overall protection from infection for both the Comirnaty only and Comirnaty/SΔRBD-LV vaccination schemes. However, the SΔRBD-LV boost indicated better protection against lung infection than the Comirnaty strategy alone. Together our findings indicate that SΔRBD is highly immunogenic and provides improved protection compared to a third mRNA boost indicative of superior antibody-based protection.

Viral Transmission in Sea Food Systems: Strategies for Control and Emerging Challenges

The SARS-CoV-2 pandemic had widespread and severe impacts on both the global economy and human health. Facing the continuously mutating virus, this crisis has heightened concerns among consumers and businesses regarding viral transmission through seafood, particularly in the face of emerging, unknown viruses, underscoring our preparedness gaps. This review provides a succinct overview of the survival mechanisms of prevalent viruses in seafood, examines potential transmission pathways to humans during seafood processing, and discusses strategies for mitigating their spread throughout the seafood supply chain. Furthermore, the discussion highlights emerging trends in innovative antiviral technologies aimed at enhancing food safety. Person-to-person transmission remains the most likely source of infection within the supply chain. Therefore, it is still imperative to adhere to the implementation of standard processes, namely good manufacturing practices (GMP) and good hygiene practices (GHP), in the seafood business. In light of the significant losses caused by this crisis and the persistent presence of various viruses within the seafood supply chain, efforts are needed to implement predictive and preventive measures against potential emerging viruses. Future research should focus on monitoring and limiting viral transmission by integrating Industry 4.0 applications, smart technologies, and antiviral packaging, maximizing the potential of these emerging solutions.

Cell-Based Relative Potency of a Respiratory Syncytial Virus mRNA Vaccine Correlates with In Vivo Immunogenicity

Background/Objectives: Potency is a critical quality attribute for vaccine development as well as clinical drug product (DP) lot release and stability testing. Animal studies have the potential to offer conclusive insights about the potency of vaccines by demonstrating technical relevance with respect to the hypothesized vaccine mode of action. However, animal studies are expensive, time-consuming, labor intensive, and, most importantly, involve the use of animals. Therefore, alternative in vitro potency assays should be explored. Methods: In this study, female BALB/c mice were immunized intramuscularly with various doses of a respiratory syncytial virus (RSV) mRNA vaccine V171 lots at day 0 and day 21. Vaccine-elicited immune responses were determined by ELISA (post-dose 1) and neutralizing assay (post-dose 2). These vaccine lots were also tested in a cell-based relative potency assay in which the ability of each lot to express the RSV F protein in Hep G2 cells was measured against a reference standard. Results: Effective Dose 50s (ED50s) of the vaccine lots were determined with probit models based on dichotomized ELISA or neutralizing titers. Statistical analysis demonstrated that the post-dose 2 neutralizing ED50 correlates with cell-based relative potency (Pearson's correlation test ln (RP) and ln (ED50): correlation coefficient = -0.82; p-value = 0.047). Conclusions: These data merit the use of a cell-based potency assay to replace the animal study to support V171 vaccine development and to use for DP lot release and stability testing. This study also establishes proof-of-concept of using cell-based potency assays as an alternative to animal immunogenicity studies for mRNA-based vaccines.

T and B cell responses in different immunization scenarios for COVID-19: a narrative review

Vaccines against COVID-19 have high efficacy and low rates of adverse events. However, none of the available vaccines provide sterilizing immunity, and reinfections remain possible. This review aims to summarize the immunological responses elicited by different immunization strategies, examining the roles of homologous and heterologous vaccination and hybrid immunity. Homologous vaccination regimens exhibit considerable variation in immune responses depending on the vaccine platform, particularly concerning antibody titers, B cell activation, and T cell responses. mRNA vaccines, such as mRNA-1273 and BNT162b2, consistently generate higher and more durable levels of neutralizing antibodies and memory B cells compared to adenovirus-based vaccines like Ad26.COV2.S and ChAdOx1. The combination of two distinct vaccine platforms, each targeting different immune pathways, seems to be more effective in promoting long-lasting B cell responses and potent T cell responses. The high heterogeneity of the available studies, the different dosing schemes, the succession of new variants, and the subjects' immunological background do not allow for a definitive conclusion. Overall, heterologous vaccination strategies, combining sequentially viral vector and mRNA may deliver a more balanced and robust humoral and cellular immune response compared to homologous regimens. Hybrid immunity, which arises from SARS-CoV-2 infection preceded or followed by vaccination produces markedly stronger immune responses than either vaccination or infection alone. The immune response to SARS-CoV-2 variants of concern varies depending on both the vaccine platform and prior infection status. Hybrid immunity leads to a broader antibody repertoire, providing enhanced neutralization of variants of concern. Heterologous vaccination and hybrid immunity may provide further opportunities to enhance immune responses, offering broader protection and greater durability of immunity. However, from all-cause mortality, symptomatic or severe COVID, and serious adverse events at present it is not possible to infer different effects between homologous and heterologous schemes. Next-generation vaccines could involve tweaks to these designs or changes to delivery mechanisms that might improve performance.

Design of SARS-CoV-2 RBD Immunogens to Focus Immune Responses Towards Conserved Coronavirus Epitopes

SARS-CoV-2 continues to evolve, with new variants emerging that evade pre-existing immunity and limit the efficacy of existing vaccines. One approach towards developing superior, variant-proof vaccines is to engineer immunogens that preferentially elicit antibodies with broad cross-reactivity against SARS-CoV-2 and its variants by targeting conserved epitopes on spike. The inner and outer faces of the Receptor Binding Domain (RBD) are two such conserved regions targeted by antibodies that recognize diverse human and animal coronaviruses. To promote the elicitation of such antibodies by vaccination, we engineered "resurfaced" RBD immunogens that contained mutations at exposed RBD residues outside the target epitopes. In the context of pre-existing immunity, these vaccine candidates aim to disfavor the elicitation of strain-specific antibodies against the immunodominant Receptor Binding Motif (RBM) while boosting the induction of inner and outer face antibodies. The engineered resurfaced RBD immunogens were stable, lacked binding to monoclonal antibodies with limited breadth, and maintained strong interactions with target broadly neutralizing antibodies. When used as vaccines, they limited humoral responses against the RBM as intended. Multimerization on nanoparticles further increased the immunogenicity of the resurfaced RBDs immunogens, thus supporting resurfacing as a promising immunogen design approach to rationally shift natural immune responses to develop more protective vaccines.

Distinct response patterns of endothelial markers to the BNT162b2 mRNA COVID-19 booster vaccine are associated with the spike-specific IgG antibody production

Introduction

Despite the efficacy and safety of SARS-CoV-2 vaccines, inflammatory and/or thrombotic episodes have been reported. Since the impact of COVID-19 vaccines on the endothelium remains uncertain, our objective was to assess endothelial activation status before and 90 days after the third dose of the BNT162b2 mRNA COVID-19 vaccine.

Methods

A prospective longitudinal study was conducted at University General Hospital of Albacete, involving 38 healthy health-care workers. Serum levels of endothelial markers (endocan and sVCAM-1) and spike S1-specific IgG antibodies were determined before and at 7, 15, 24 and 90days following vaccination. To analyze each participant´s individual response, we calculated relative increases/decreases (delta values) in endothelial markers and antibodies concentrations compared to their pre-vaccination levels.

Results

We identified two significantly distinct profiles of endothelial markers response, characterized by either increased or decreased serum levels of endocan and sVCAM. Incremental and decremental response groups did not differ in terms of age, sex, cardiovascular risk factors, previous SARS-CoV-2 infection and influenza vaccine co-administration. However, these responses were significantly associated with the relative spike-specific antibody production. Specifically, the greatest relative increase in antibodies was found in the decremental responders. Additionally, the higher delta antibody production was observed in non-previously infected individuals.

Conclusion

Administration of the BNT162b2 booster vaccine triggered a non-homogenous response of endothelial function markers among the study participants. Our findings improve the understanding of individual responses to the mRNA COVID-19 booster vaccine, which could be useful in assessing the need for booster doses, particularly in population at risk of vascular complications.

Real-world assessment of reinfection with SARS-CoV-2: Implications for vaccines

BACKGROUND

There have been over 670 million confirmed cases of SARS-CoV-2 infection globally, resulting in over 6.87 million deaths. With approximately 0.1 %-6.8 % experiencing reinfection. This retrospective cohort study aimed to compare the risk of short-term circulatory and respiratory sequelae between SARS-CoV-2 reinfection and initial infection, and assess the impact of vaccination.

METHOD

Data from the TriNetX US Collaborative network (2020-2022) were used to create two cohorts based on reinfection status. The main outcome assessed were medical utilization, circulatory and respiratory symptoms, and circulatory and respiratory diseases. The Kaplan-Meier method was used to compare the risks between two cohorts. Four subgroup analyses (vaccination status, age, sex, race) and six sensitivity analyses (rigorous definition, modified exclusion criteria, treatment, different COVID-19 variants timeline, address survivorship bias, and E-value calculation) were also conducted.

RESULTS

The reinfection cohort showed a significant reduction in medical utilization [ Hazard ratio, HR: 0.867, (95 % confidence interval, CI:0.839-0.896) for hospitalization, 0.488 (0.418-0.570) for critical care services, and 0.476 (0.360-0.629) for mechanical ventilation], lower risk of circulatory diseases [ HR: 0.701 (95 % CI:0.637-0.772), 0.695 (0.583-0.829), 0.660 (0.605-0.719), 0.741 (0.644-0.854), 0.614 (0.535-0.705), and 0.758 (0.656-0.876) for ischemic heart disease, inflammatory heart disease, dysrhythmias, venous thromboembolism, other cardiac disorders, and cerebrovascular diseases, respectively], and lower risk of respiratory diseases such as pneumonia, other acute lower respiratory infections, asthma, and hypoxemia [HR: 0.302 (95 % CI: 0.273-0.333), 0.811 (0.686-0.958), 0.791 (0.735-0.850), and 0.392 (0.338-0.455), respectively]. The vaccinated reinfection cohort showed no significant differences in medical utilization, circulatory diseases, or respiratory conditions but had a higher risk of breathing abnormalities. breathing abnormalities [HR: 1.195 (95 % CI:1.087-1.313)].

CONCLUSIONS

The individuals who experienced reinfection exhibited milder short-term sequelae in the circulatory and respiratory systems. Vaccine administration protects against cardiovascular or respiratory systems.

The Second Round of a Population-Based Seroprevalence Study of Anti-SARS-CoV-2 Antibodies and COVID-19 Vaccination Assessment in the Republika Srpska, Bosnia and Herzegovina

INTRODUCTION

The aim of the study was to assess the seroprevalence of SARS-CoV-2 in the Republika Srpska, Bosnia and Herzegovina, after five waves of COVID-19 and 1 year after introduction of vaccination to better understand the true extent of the COVID-19 pandemic in the population of the Republika Srpska and role of vaccination in achieving herd immunity.

METHODS

The population-based study was conducted from December 2021 to February 2022 in a group of 4463 individuals in the Republika Srpska. Total anti-SARS-CoV-2 antibodies were determined in serum specimens using the Wantai total antibody ELISA assay. Quantitative analysis, using Kantaro IgG assays, was performed in subsamples (1273 specimens) to asses and compare levels of IgG among vaccinated, recovered and participants with hybrid immunity. To adjust for age and gender distribution in sample, poststratification method is applied.

RESULTS

The overall cumulative seroprevalence was 94.6% (95% CI = 93.9-95.3). Significantly higher seroprevalence rates were observed among vaccinated 97.8% (95% CI = 97.3-98.4) comparing to unvaccinated participants (89.5%, 95% CI = 88.0-91.0). Seroprevalence increases with the number of received doses. Among various professions, the highest seroprevalence was found in the service industry (98.1%), education (98.0%) and healthcare (96.9%). We found that 2.2% of vaccinated and 3.6% of participants with SARS-CoV-2 positivity during 2021 had no detectable IgG antibodies. Both seroprevalence (98.6%) and antibody titres (1094.4 AU/mL) were significantly higher among people with hybrid immunity.

CONCLUSION

Our findings reveal a 2.3-fold increase in seroprevalence of SARS-CoV-2 antibodies due to infection and vaccination, comparing to the first study performed 1 year earlier. This study provides better understanding of the SARS-CoV-2 transmission and highlights the important role of the vaccination in achieving the population immunity. Periodically conducted population-based seroprevalence studies are important to understand temporal trends and assess surveillance system performance and public compliance with vaccination policies.

COVID-19 vaccines: Immune correlates and clinical outcomes

Severe disease due to COVID-19 has declined dramatically as a result of widespread vaccination and natural immunity in the population. With the emergence of SARS-CoV-2 variants that largely escape vaccine-elicited neutralizing antibody responses, the efficacy of the original vaccines has waned and has required vaccine updating and boosting. Nevertheless, hospitalizations and deaths due to COVID-19 have remained low. In this review, we summarize current knowledge of immune responses that contribute to population immunity and the mechanisms how vaccines attenuate COVID-19 disease severity.

Protein nanoparticle vaccines induce potent neutralizing antibody responses against MERS-CoV

Middle East respiratory syndrome coronavirus (MERS-CoV) is a betacoronavirus that causes severe respiratory illness in humans. There are no licensed vaccines against MERS-CoV and only a few candidates in phase I clinical trials. Here, we develop MERS-CoV vaccines utilizing a computationally designed protein nanoparticle platform that has generated safe and immunogenic vaccines against various enveloped viruses, including a licensed vaccine for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Two-component nanoparticles displaying spike (S)-derived antigens induce neutralizing responses and protect mice against challenge with mouse-adapted MERS-CoV. Epitope mapping reveals the dominant responses elicited by immunogens displaying the prefusion-stabilized S-2P trimer, receptor binding domain (RBD), or N-terminal domain (NTD). An RBD nanoparticle elicits antibodies targeting multiple non-overlapping epitopes in the RBD. Our findings demonstrate the potential of two-component nanoparticle vaccine candidates for MERS-CoV and suggest that this platform technology could be broadly applicable to betacoronavirus vaccine development.

Isolation and escape mapping of broadly neutralizing antibodies against emerging delta-coronaviruses

Porcine delta-coronavirus (PDCoV) spillovers were recently detected in febrile children, underscoring the recurrent zoonoses of divergent CoVs. To date, no vaccines or specific therapeutics are approved for use in humans against PDCoV. To prepare for possible future PDCoV epidemics, we isolated PDCoV spike (S)-directed monoclonal antibodies (mAbs) from humanized mice and found that two, designated PD33 and PD41, broadly neutralized a panel of PDCoV variants. Cryoelectron microscopy (cryo-EM) structures of PD33 and PD41 in complex with the S receptor-binding domain (RBD) and ectodomain trimer revealed the epitopes recognized by these mAbs, rationalizing their broad inhibitory activity. We show that both mAbs competitively interfere with host aminopeptidase N binding to neutralize PDCoV and used deep-mutational scanning epitope mapping to associate RBD antigenic sites with mAb-mediated neutralization potency. Our results indicate a PD33-PD41 mAb cocktail may heighten the barrier to escape. PD33 and PD41 are candidates for clinical advancement against future PDCoV outbreaks.

Super broad and protective nanobodies against Sarbecoviruses including SARS-CoV-1 and the divergent SARS-CoV-2 subvariant KP.3.1.1

The ongoing evolution and immune escape of SARS-CoV-2, alongside the potential threat of SARS-CoV-1 and other sarbecoviruses, underscore the urgent need for effective strategies against their infection and transmission. This study highlights the discovery of nanobodies from immunized alpacas, which demonstrate exceptionally broad and potent neutralizing capabilities against the recently emerged and more divergent SARS-CoV-2 Omicron subvariants including JD.1.1, JN.1, KP.3, KP.3.1.1, as well as SARS-CoV-1 and coronaviruses from bats and pangolins utilizing receptor ACE2. Among these, Tnb04-1 emerges as the most broad and potent, binding to a conserved hydrophobic pocket in the spike's receptor-binding domain, distinct from the ACE2 binding site. This interaction disrupts the formation of a proteinase K-resistant core, crucial for viral-cell fusion. Notably, intranasal administration of Tnb04-1 in Syrian hamsters effectively prevented respiratory infection and transmission of the authentic Omicron XBB.1.5 subvariant. Thus, Thb04-1 holds promise in combating respiratory acquisition and transmission of diverse sarbecoviruses.

Evaluating the Quality of Studies Assessing COVID-19 Vaccine Neutralizing Antibody Immunogenicity

Objective: COVID-19 vaccine-neutralizing antibodies provide early data on potential vaccine effectiveness, but their usefulness depends on study reliability and reporting quality. Methods: We systematically evaluated 50 published post-vaccination neutralizing antibody studies for key parameters that determine study and data quality regarding sample size, SARS-CoV-2 infection, vaccination regimen, sample collection period, demographic characterization, clinical characterization, experimental protocol, live virus and pseudo-virus details, assay standardization, and data reporting. Each category was scored from very high to low or unclear quality, with the lowest score determining the overall study quality score. Results: None of the studies attained an overall high or very high score, 8% (n = 4) attained moderate, 42% (n = 21) low, and 50% (n = 25) unclear. The categories with the fewest studies assessed as ≥ high quality were SARS-CoV-2 infection (42%), sample size (30%), and assay standardization (14%). Overall quality was similar over time. No association between journal impact factor and quality score was found. Conclusions: We found that reporting in neutralization studies is widely incomplete, limiting their usefulness for downstream analyses.

Humoral and cellular immune responses in vaccinated and unvaccinated children following SARS-CoV-2 Omicron infection

Objectives

The immune response in children elicited by SARS-CoV-2 Omicron infection alone or in combination with COVID-19 vaccination (hybrid immunity) is poorly understood. We examined the humoral and cellular immune response following SARS-CoV-2 Omicron infection in unvaccinated children and children who were previously vaccinated with COVID-19 mRNA vaccine.

Methods

Participants were recruited as part of a household cohort study conducted during the Omicron predominant wave (Jan to July 2022) in Victoria, Australia. Blood samples were collected at 1, 3, 6 and 12 months following COVID-19 diagnosis. Humoral immune responses to SARS-CoV-2 Spike proteins from Wuhan, Omicron BA.1, BA.4/5 and JN.1, as well as cellular immune responses to Wuhan and BA.1 were assessed.

Results

A total of 43 children and 113 samples were included in the analysis. Following Omicron infection, unvaccinated children generated low antibody responses but elicited Spike-specific CD4 and CD8 T-cell responses. In contrast, vaccinated children infected with the Omicron variant mounted robust humoral and cellular immune responses to both ancestral strain and Omicron subvariants. Hybrid immunity persisted for at least 6 months post infection, with cellular immune memory characterised by the generation of Spike-specific polyfunctional CD8 T-cell responses.

Conclusion

SARS-CoV-2 hybrid immunity in children is characterised by persisting SARS-CoV-2 antibodies and robust CD4 and CD8 T-cell activation and polyfunctional responses. Our findings contribute to understanding hybrid immunity in children and may have implications regarding COVID-19 vaccination and SARS-CoV-2 re-infections.

Diversified humoral immunity and impacts of booster vaccines: SARS-CoV-2 antibody profile and Omicron BA.2 neutralization before and after first or second boosters

This study aims to investigate humoral immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and assess the impact of booster vaccines. We recruited individuals scheduled to receive either the first (original formula) or the second (bivalent) booster following the initial two-dose SARS-CoV-2 vaccination. We tested for IgG antibodies targeting the spike protein receptor-binding domain (RBD), S1, S2, and nucleocapsid protein, as well as for neutralizing antibodies against Omicron BA.2, before and 14-28 days after receiving the boosters. One year after receiving the initial series of vaccinations, all participants maintained anti-RBD/S1 antibodies. However, levels were lower in individuals who were vaccinated only compared to those who had both vaccination and prior infection (hybrid immunity). Participants with hybrid immunity also showed higher retention of neutralizing antibodies (93% compared to 24% in vaccine-only individuals). Even before receiving any booster shots, participants with hybrid immunity had antibody levels similar to those of vaccine-only individuals after their first booster. After receiving booster shots, antibody levels at 14-28 days were similar regardless of the number of boosters or the type of immunity. About 1 year after the first booster, all participants maintained neutralizing antibodies, and vaccine-only individuals retained about 10 times higher levels of binding antibodies than those without a booster. Humoral immunity varies widely among individuals, and vaccination planning should consider both vaccination and infection history. Boosters are beneficial for increasing antibody levels to ensure sufficient protection against infection and helping bridge the immunity gap between vaccine-only and hybrid immunity.IMPORTANCEAs we move into the era of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine boosters and shifting from pandemic to endemic, the landscape has changed for both the circulating SARS-CoV-2 variants and population immunity. Even though recent waves of infection have been clinically milder than earlier variants due to the high levels of population immunity and the properties of the Omicron subvariants, vaccination remains crucial for managing COVID-19 in the post-pandemic era. Our study unveils significant variations in the retention of anti-SARS-CoV-2 binding antibody profiles and neutralizing antibody levels 1 year after the primary and the first booster mRNA vaccination. It adds new information regarding how boosters change antibody levels and durability in individuals with hybrid (vaccination plus infection) or vaccine-only (never-infected) immunity. The findings can shed light on future vaccination planning.

T-Cell Immune Responses to SARS-CoV-2 Infection and Vaccination

The innate and adaptive immune systems collaborate to detect SARS-CoV-2 infection, minimize the viral spread, and kill infected cells, ultimately leading to the resolution of the infection. The adaptive immune system develops a memory of previous encounters with the virus, providing enhanced responses when rechallenged by the same pathogen. Such immunological memory is the basis of vaccine function. Here, we review the current knowledge on the immune response to SARS-CoV-2 infection and vaccination, focusing on the pivotal role of T cells in establishing protective immunity against the virus. After providing an overview of the immune response to SARS-CoV-2 infection, we describe the main features of SARS-CoV-2-specific CD4+ and CD8+ T cells, including cross-reactive T cells, generated in patients with different degrees of COVID-19 severity, and of Spike-specific CD4+ and CD8+ T cells induced by vaccines. Finally, we discuss T-cell responses to SARS-CoV-2 variants and hybrid immunity and conclude by highlighting possible strategies to improve the efficacy of COVID-19 vaccination.

SARS-CoV-2 infection prior to vaccination amplifies Fc-mediated humoral profiles in an age-dependent manner

Immunity acquired by vaccination following infection, termed hybrid immunity, has been shown to confer enhanced protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by enhancing the breadth and potency of immune responses. Here, we assess Fc-mediated humoral profiles in hybrid immunity and their association with age and vaccine type. Participants are divided into three groups: infection only, vaccination only, and vaccination following infection (i.e., hybrid immunity). Using systems serology, we profile humoral immune responses against spikes and subdomains of SARS-CoV-2 variants. We find that hybrid immunity is characterized by superior Fc receptor binding and natural killer (NK) cell-, neutrophil-, and complement-activating antibodies, which is higher than what can be expected from the sum of the vaccination and infection. These differences between hybrid immunity and vaccine-induced immunity are more pronounced in aged adults, especially for immunoglobulin (Ig)G1, IgG2, and Fcγ receptor-binding antibodies. Our findings suggest that vaccination strategies that aim to mimic hybrid immunity should consider age as an important modifier.

Longevity of hybrid immunity against SARS-CoV-2 in adults vaccinated with an adenovirus-based COVID-19 vaccine

BACKGROUND

Hybrid immunity provides better protection against COVID-19 than vaccination or prior natural infection alone. It induces high magnitude and broadly cross-reactive neutralising anti-Spike IgG antibodies. However, it is not clear how long these potent antibodies last, especially in the context of adenovirus-based COVID-19 vaccines.

METHODS

We conducted a longitudinal cohort study and enrolled 20 adults who had received an adenovirus-based COVID-19 vaccine before a laboratory-confirmed SARS-CoV-2 infection. We followed up the study participants for 390 days post the initial breakthrough infection. We assessed the longevity and cross-reactive breadth of serum antibodies against SARS-CoV-2 variants of concern (VOCs), including Omicron.

RESULTS

The binding anti-Spike IgG antibodies remained within the reported putative levels for at least 360 days and were cross-neutralising against Beta, Gamma, Delta, and Omicron. During the follow up period, a median of one SARS-CoV-2 re-infection event was observed across the cohort, but none resulted in severe COVID-19. Moreover, the re-exposure events were associated with augmented anti-Spike and anti-RBD IgG antibody titres.

CONCLUSIONS

This study confirms that hybrid immunity provides durable broadly cross-reactive antibody immunity against SARS-CoV-2 variants of concern for at least a year (360 days), and that it is further augment by SARS-CoV-2 re-exposure.

Omicron COVID-19 immune correlates analysis of a third dose of mRNA-1273 in the COVE trial

In the phase 3 Coronavirus Efficacy (COVE) trial (NCT04470427), post-dose two Ancestral Spike-specific binding (bAb) and neutralizing (nAb) antibodies were shown to be correlates of risk (CoR) and of protection against Ancestral-lineage COVID-19 in SARS-CoV-2 naive participants. In the SARS-CoV-2 Omicron era, Omicron subvariants with varying degrees of immune escape now dominate, seropositivity rates are high, and booster doses are administered, raising questions on whether and how these developments affect the bAb and nAb correlates. To address these questions, we assess post-boost BA.1 Spike-specific bAbs and nAbs as CoRs and as correlates of booster efficacy in COVE. For naive individuals, bAbs and nAbs inversely correlate with Omicron COVID-19: hazard ratios (HR) per 10-fold marker increase (95% confidence interval) are 0.16 (0.03, 0.79) and 0.31 (0.10, 0.96), respectively. In non-naive individuals the analogous results are similar: 0.15 (0.04, 0.63) and 0.28 (0.07, 1.08). For naive individuals, three vs two-dose booster efficacy correlates with predicted nAb titer at exposure, with estimates -8% (-126%, 48%), 50% (25%, 67%), and 74% (49%, 87%), at 56, 251, and 891 Arbitrary Units/ml. These results support the continued use of antibody as a surrogate endpoint.

The role of convalescent plasma and hyperimmune immunoglobulins in the COVID-19 pandemic, including implications for future preparedness

Introduction

When Coronavirus Disease-19 (COVID-19) struck the world in December 2019, initiatives started to investigate the efficacy of convalescent plasma, a readily available source of passive antibodies, collected from recovered patients as a therapeutic option. This was based on historical observational data from previous virus outbreaks.

Methods

A scoping review was conducted on the efficacy and safety of convalescent plasma and hyperimmune immunoglobulins for COVID-19 treatment. This review included the latest Cochrane systematic review update on 30-day mortality and safety. We also covered use in pediatric and immunocompromised patients, as well as the logistic challenges faced in donor recruitment and plasma collection in general. Challenges for low resource countries were specifically highlighted.

Results

A major challenge is the high donation frequency required from first-time donors to ensure a safe product, which minimizes the risk of transfusion-transmitted infectious. This is particularly difficult in low- and middle- income countries due to inadequate infrastructure and insufficient blood product supplies. High-certainty evidence indicates that convalescent plasma does not reduce mortality or significantly improve clinical outcomes in patients with moderate to severe COVID-19 infection. However, CCP may provide a viable treatment for patients unable to mount an endogenous immune response to SARS-CoV-2, based on mostly observational studies and subgroup data of published and ongoing randomized trials. Convalescent plasma has been shown to be safe in adults and children with COVID-19 infection. However, the efficacy in pediatric patients remains unclear.

Discussion

Data on efficacy and safety of CCP are still underway in ongoing (randomized) studies and by reporting the challenges, limitations and successes encountered to-date, research gaps were identified to be addressed for the future.

Conclusion

This experience serves as a valuable example for future pandemic preparedness, particularly when therapeutic options are limited, and vaccines are either being developed or ineffective due to underlying immunosuppression.

Natural malaria infection elicits rare but potent neutralizing antibodies to the blood-stage antigen RH5

Plasmodium falciparum reticulocyte-binding protein homolog 5 (RH5) is the most advanced blood-stage malaria vaccine candidate and is being evaluated for efficacy in endemic regions, emphasizing the need to study the underlying antibody response to RH5 during natural infection, which could augment or counteract responses to vaccination. Here, we found that RH5-reactive B cells were rare, and circulating immunoglobulin G (IgG) responses to RH5 were short-lived in malaria-exposed Malian individuals, despite repeated infections over multiple years. RH5-specific monoclonal antibodies isolated from eight malaria-exposed individuals mostly targeted non-neutralizing epitopes, in contrast to antibodies isolated from five RH5-vaccinated, malaria-naive UK individuals. However, MAD8-151 and MAD8-502, isolated from two malaria-exposed Malian individuals, were among the most potent neutralizers out of 186 antibodies from both cohorts and targeted the same epitopes as the most potent vaccine-induced antibodies. These results suggest that natural malaria infection may boost RH5-vaccine-induced responses and provide a clear strategy for the development of next-generation RH5 vaccines.

Long-Term Immunity against SARS-CoV-2 Wild-Type and Omicron XBB.1.5 in Indonesian Residents after Vaccination and Infection

In the post-pandemic era, evaluating long-term immunity against COVID-19 has become increasingly critical, particularly in light of continuous SARS-CoV-2 mutations. This study aimed to assess the long-term humoral immune response in sera collected in Makassar. We measured anti-RBD IgG levels and neutralization capacity (NC) against both the Wild-Type (WT) Wuhan-Hu and Omicron XBB.1.5 variants across groups of COVID-19-vaccinated individuals with no booster (NB), single booster (SB), and double booster (DB). The mean durations since the last vaccination were 25.11 months, 19.24 months, and 16.9 months for the NB, SB, and DB group, respectively. Additionally, we evaluated the effect of breakthrough infection (BTI) history, with a mean duration since the last confirmed infection of 21.72 months. Our findings indicate fair long-term WT antibody (Ab) titers, with the DB group showing a significantly higher level than the other groups. Similarly, the DB group demonstrated the highest anti-Omicron XBB.1.5 Ab titer, yet it was insignificantly different from the other groups. Although the level of anti-WT Ab titers was moderate, we observed near-complete (96-97%) long-term neutralization against the WT pseudo-virus for all groups. There was a slight decrease in NC against Omicron XBB.1.5 compared to the WT among all groups, as DB group, SB group, and NB group showed 80.71 ± 3.9%, 74.29 ± 6.7%, and 67.2 ± 6.3% neutralization activity, respectively. A breakdown analysis based on infection and vaccine status showed that booster doses increase the NC against XBB.1.5, particularly in individuals without BTI. Individuals with BTI demonstrate a better NC compared to their counterpart uninfected individuals with the same number of booster doses. Our findings suggest that long-term immunity against SARS-CoV-2 persists and is effective against the mutant variant. Booster doses enhance the NC, especially among uninfected individuals.

Hybrid immunity to SARS-CoV-2 arises from serological recall of IgG antibodies distinctly imprinted by infection or vaccination

We describe the molecular-level composition of polyclonal immunoglobulin G (IgG) anti-spike antibodies from ancestral severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, vaccination, or their combination ("hybrid immunity") at monoclonal resolution. Infection primarily triggers S2/N-terminal domain (NTD)-reactive antibodies, whereas vaccination mainly induces anti-receptor-binding domain (RBD) antibodies. This imprint persists after secondary exposures wherein >60% of ensuing hybrid immunity derives from the original IgG pool. Monoclonal constituents of the original IgG pool can increase breadth, affinity, and prevalence upon secondary exposures, as exemplified by the plasma antibody SC27. Following a breakthrough infection, vaccine-induced SC27 gained neutralization breadth and potency against SARS-CoV-2 variants and zoonotic viruses (half-maximal inhibitory concentration [IC50] ∼0.1-1.75 nM) and increased its binding affinity to the protective RBD class 1/4 epitope (dissociation constant [KD] < 5 pM). According to polyclonal escape analysis, SC27-like binding patterns are common in SARS-CoV-2 hybrid immunity. Our findings provide a detailed molecular definition of immunological imprinting and show that vaccination can produce class 1/4 (SC27-like) IgG antibodies circulating in the blood.

Protective mucosal SARS-CoV-2 antibodies in the majority of the general population in the Netherlands

Antibodies to SARS-CoV-2 on the mucosal surfaces of the respiratory tract are understood to contribute to protection against SARS-CoV-2 infection. We aimed to describe the prevalence, levels, and functionality of mucosal antibodies in the general Dutch population. Nasal samples were collected from 778 randomly selected participants, 1-90 years of age, nested within the nationwide prospective SARS-CoV-2 PIENTER corona serosurvey in the Netherlands. Spike-specific immunoglobulin (Ig)G was detected in the nasal samples of 94.6% (in case of the wild-type S1 variant) and 94.9% (Omicron BA.1) of the individuals, whereas 44.2% and 62.7% of the individuals were positive for wild-type and Omicron BA.1 S1 IgA, respectively. The lowest prevalence of mucosal antibodies was observed in children under 12 years of age. The prevalence and levels of IgA and IgG were higher in individuals with a history of SARS-CoV-2 infection. Mucosal antibodies inhibited the binding of Wuhan, Delta, and Omicron BA.1 receptor binding domain to human angiotensin-converting enzyme 2 in 94.4%, 95.4%, and 92.6% of the participants, respectively. Higher levels of mucosal antibodies were associated with a lower risk of future infection.

Deciphering Fc-effector functions against SARS-CoV-2

Major efforts were deployed to study the antibody response against SARS-CoV-2. Antibodies neutralizing SARS-CoV-2 have been extensively studied in the context of infections, vaccinations, and breakthrough infections. Antibodies, however, are pleiotropic proteins that have many functions in addition to neutralization. These include Fc-effector functions such as antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). Although important to combat viral infections, these Fc-effector functions were less studied in the context of SARS-CoV-2 compared with binding and neutralization. This is partly due to the difficulty in developing reliable assays to measure Fc-effector functions compared to antibody binding and neutralization. Multiple assays have now been developed and can be used to measure different Fc-effector functions. Here, we review these assays and what is known regarding anti-SARS-CoV-2 Fc-effector functions. Overall, this review summarizes and updates our current state of knowledge regarding anti-SARS-CoV-2 Fc-effector functions.

Persistent differences in the immunogenicity of the two COVID-19 primary vaccines series, modulated by booster mRNA vaccination and breakthrough infection

INTRODUCTION

The long-term impact of initial immunogenicity induced by different primary COVID-19 vaccine series remains unclear.

METHODS

A prospective cohort study was conducted at 10 tertiary hospitals in Korea from March 2021 to September 2022. Immunogenicity assessments included anti-spike protein antibody (Sab), SARS-CoV-2-specific interferon-gamma releasing assay (IGRA), and multiplex cytokine assays for spike protein-stimulated plasma. Spike proteins derived from wild-type SARS-CoV-2 and alpha variant (Spike1) and beta and gamma variant (Spike2) were utilized.

RESULTS

A total of 235 healthcare workers who had received a two-dose primary vaccine series of either ChAdOx1 or BNT162b2, followed by a third booster dose of BNT162b2 (166 in the ChAdOx1/ChAdOx1/BNT162b2 (CCB) group and 69 in the BNT162b2/BNT162b2/BNT162b2 (BBB) group, based on the vaccine series) were included. Following the primary vaccine series, the BBB group exhibited significantly higher increases in Sab levels, IGRA responses, and multiple cytokines (CCL2/MCP-1, CCL3/MIP-1α, CCL4/MIP-1β, interleukin (IL)-1ra, IFN-γ, IL-2, IL-4, and IL-10) compared to the CCB group (all P < 0.05). One month after the third BNT162b2 booster, the CCB group showed Sab levels comparable to those of the BBB group, and both groups exhibited lower levels after six months without breakthrough infections (BIs). However, among those who experienced BA.1/2 BIs after the third booster, Sab levels increased significantly more in the BBB group than in the CCB group (P < 0.001). IGRA responses to both Spike1 and Spike2 proteins were significantly stronger in the BBB group than the CCB group after the third booster, while only the Spike2 response were higher after BIs (P = 0.007). The BBB group exhibited stronger enhancement of T-cell cytokines (IL-2, IL-4, and IL-17A) after BIs than in the CCB group (P < 0.05).

CONCLUSION

Differences in immunogenicity induced by the two primary vaccine series persisted, modulated by subsequent booster vaccinations and BIs.

Aerosol Inhalation of Gene Delivery Therapy for Pulmonary Diseases

Gene delivery therapy has emerged as a popular approach for the treatment of various diseases. However, it still poses the challenges of accumulation in target sites and reducing off-target effects. Aerosol gene delivery for the treatment of pulmonary diseases has the advantages of high lung accumulation, specific targeting and fewer systemic side effects. However, the key challenge is selecting the appropriate formulation for aerosol gene delivery that can overcome physiological barriers. There are numerous existing gene carriers under study, including viral vectors and non-viral vectors. With the development of biomaterials, more biocompatible substances have applied gene delivery via inhalation. Furthermore, many types of genes can be delivered through aerosol inhalation, such as DNA, mRNA, siRNA and CRISPR/Cas9. Aerosol delivery of different types of genes has proven to be efficient in the treatment of many diseases such as SARS-CoV-2, cystic fibrosis and lung cancer. In this paper, we provide a comprehensive review of the ongoing research on aerosol gene delivery therapy, including the basic respiratory system, different types of gene carriers, different types of carried genes and clinical applications.

Diversification of the VH3-53 immunoglobulin gene segment by somatic hypermutation results in neutralization of SARS-CoV-2 virus variants

COVID-19 induces re-circulating long-lived memory B cells (MBC) that, upon re-encounter with the pathogen, are induced to mount immunoglobulin responses. During convalescence, antibodies are subjected to affinity maturation, which enhances the antibody binding strength and generates new specificities that neutralize virus variants. Here, we performed a single-cell RNA sequencing analysis of spike-specific B cells from a SARS-CoV-2 convalescent subject. After COVID-19 vaccination, matured infection-induced MBC underwent recall and differentiated into plasmablasts. Furthermore, the transcriptomic profiles of newly activated B cells transiently shifted toward the ones of atypical and CXCR3+ B cells and several B-cell clonotypes massively expanded. We expressed monoclonal antibodies (mAbs) from all B-cell clones from the largest clonotype that used the VH3-53 gene segment. The in vitro analysis revealed that some somatic hypermutations enhanced the neutralization breadth of mAbs in a putatively stochastic manner. Thus, somatic hypermutation of B-cell clonotypes generates an anticipatory memory that can neutralize new virus variants.

A broad neutralizing nanobody against SARS-CoV-2 engineered from an approved drug

SARS-CoV-2 infection is initiated by Spike glycoprotein binding to the human angiotensin-converting enzyme 2 (ACE2) receptor via its receptor binding domain. Blocking this interaction has been proven to be an effective approach to inhibit virus infection. Here we report the discovery of a neutralizing nanobody named VHH60, which was directly produced from an engineering nanobody library based on a commercialized nanobody within a very short period. VHH60 competes with human ACE2 to bind the receptor binding domain of the Spike protein at S351, S470-471and S493-494 as determined by structural analysis, with an affinity of 2.56 nM. It inhibits infections of both ancestral SARS-CoV-2 strain and pseudotyped viruses harboring SARS-CoV-2 wildtype, key mutations or variants at the nanomolar level. Furthermore, VHH60 suppressed SARS-CoV-2 infection and propagation 50-fold better and protected mice from death for twice as long as the control group after SARS-CoV-2 nasal infections in vivo. Therefore, VHH60 is not only a powerful nanobody with a promising profile for disease control but also provides evidence for a highly effective and rapid approach to generating therapeutic nanobodies.

Characteristics and Functions of Infection-enhancing Antibodies to the N-terminal Domain of SARS-CoV-2

Background

Fcγ-receptor (FcγR)-independent enhancement of SARS-CoV-2 infection mediated by N-terminal domain (NTD)-binding monoclonal antibodies (mAbs) has been observed in vitro, but the functional significance of these antibodies in vivo is less clear.

Methods

We characterized 1,213 SARS-CoV-2 spike (S)-binding mAbs derived from COVID-19 convalescent patients for binding specificity to the SARS-CoV-2 S protein, VH germ-line usage, and affinity maturation. Infection enhancement in a vesicular stomatitis virus (VSV)-SARS-CoV-2 S pseudovirus (PV) assay was characterized in respiratory and intestinal epithelial cell lines, and against SARS-CoV-2 variants of concern (VOC). Proteomic deconvolution of the serum antibody repertoire was used to determine functional attributes of secreted NTD-binding mAbs.

Results

We identified 72/1213 (5.9%) mAbs that enhanced SARS-CoV-2 infection in a PV assay. The majority (68%) of these mAbs recognized the NTD, were identified in patients with mild and severe disease, and persisted for at least 5 months post-infection. Infection enhancement by NTD-binding mAbs was not observed in intestinal and respiratory epithelial cell lines and was diminished or lost against SARS-CoV-2 VOC. Proteomic deconvolution of the serum antibody repertoire from 2 of the convalescent patients identified, for the first time, NTD-binding, infection-enhancing mAbs among the circulating immunoglobulins directly isolated from serum. Functional analysis of these mAbs demonstrated robust activation of FcγRIIIa associated with antibody binding to recombinant S proteins.

Conclusions

Functionally active NTD-specific mAbs arise frequently during natural infection and can last as major serum clonotypes during convalescence. These antibodies display functional attributes that include FcγR activation, and may be selected against by mutations in NTD associated with SARS-CoV-2 VOC.

Immunogenicity of Monovalent mRNA-1273 and BNT162b2 Vaccines in Children <5 Years of Age

BACKGROUND AND OBJECTIVES

The messenger RNA (mRNA)-based coronavirus disease 2019 vaccines approved for use in children <5 years of age have different antigen doses and administration schedules that could affect vaccine immunogenicity and effectiveness. We sought to compare the strength and breadth of serum binding and neutralizing antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) elicited by monovalent mRNA-based coronavirus disease 2019 vaccines in young children.

METHODS

We conducted a prospective cohort study of children 6 months to 4 years of age who completed primary series vaccination with monovalent mRNA-1273 or BNT162b2 vaccines. Serum was collected 1 month after primary vaccine series completion for the measurement of SARS-CoV-2-specific humoral immune responses, including antibody binding responses to Spike proteins from an ancestral strain (D614G) and major variants of SARS-CoV-2 and antibody neutralizing activity against D614G and Omicron subvariants (BA.1, BA.4/5).

RESULTS

Of 75 participants, 40 (53%) received mRNA-1273 and 35 (47%) received BNT162b2. Children receiving either primary vaccine series developed robust and broad SARS-CoV-2-specific binding and neutralizing antibodies, including to Omicron subvariants. Children with a previous history of SARS-CoV-2 infection developed significantly higher antibody binding responses and neutralization titers to Omicron subvariants, which is consistent with the occurrence of identified infections during the circulation of Omicron subvariants in the region.

CONCLUSIONS

Monovalent mRNA-1273 and BNT162b2 elicited similar antibody responses 1 month after vaccination in young children. In addition, previous infection significantly enhanced the strength of antibody responses to Omicron subvariants. The authors of future studies should evaluate incorporation of these vaccines into the standard childhood immunization schedule.

Functional antibody responses targeting the Spike protein of SARS-CoV-2 Omicron XBB.1.5 in elderly nursing home residents following Wuhan-Hu-1-based mRNA booster vaccination

The immune effector mechanisms involved in protecting against severe COVID-19 infection in elderly nursing home residents following vaccination or natural infection are not well understood. Here, we measured SARS-CoV-2 Spike (S)-directed functional antibody responses, including neutralizing antibodies (NtAb) and antibody Fc-mediated NK cell activity (degranulation and IFNγ production), against the Wuhan-Hu-1, BA.4/5 (for NtAb), and Omicron XBB.1.5 variants in elderly nursing home residents (n = 39; median age, 91 years) before and following a third (pre- and post-3D) and a fourth (pre- and post-4D) mRNA COVID-19 vaccine dose. Both 3D and 4D boosted NtAb levels against both (sub)variants. Likewise, 3D and 4D increased the ability of sera to trigger both LAMP1- and IFNγ-producing NK cells, in particular against XBB.1.5. In contrast to NtAb titres, the frequencies of LAMP1- and IFNγ-producing NK cells activated by antibodies binding to Wuhan-Hu-1 and Omicron XBB.1.5 S were comparable at all testing times. Stronger functional antibody responses were observed in vaccine-experienced participants compared to vaccine-naïve at some testing times. These findings can contribute to identifying a reliable correlate of protection in elderly nursing home residents against severe COVID-19 and inform future vaccine strategies in this population group.

Impact of Prior COVID-19 Immunization and/or Prior Infection on Immune Responses and Clinical Outcomes

Cellular and humoral immunity exhibit dynamic adaptation to the mutating SARS-CoV-2 virus. It is noteworthy that immune responses differ significantly, influenced by whether a patient has received vaccination or whether there is co-occurrence of naturally acquired and vaccine-induced immunity, known as hybrid immunity. The different immune reactions, conditional on vaccination status and the viral variant involved, bear implications for inflammatory responses, patient outcomes, pathogen transmission rates, and lingering post-COVID conditions. Considering these developments, we have performed a review of recently published literature, aiming to disentangle the intricate relationships among immunological profiles, transmission, the long-term health effects post-COVID infection poses, and the resultant clinical manifestations. This investigation is directed toward understanding the variability in the longevity and potency of cellular and humoral immune responses elicited by immunization and hybrid infection.

Neutralizing antibody responses to the Delta variant of SARS-CoV-2 following vaccination with Ad5-nCoV (CanSino) in the Mexican population

During the COVID-19 pandemic, the Ad5-nCoV vaccine was applied to the Mexican population before the WHO approved it. In a transversal study, we compare the CanSino vaccine efficacy and a natural SARS-CoV-2 infection in eliciting neutralizing antibodies against the SARS-CoV-2 Delta variant in Guadalajara, Mexico. Participants between 30-60 years were included in the study and classified into three groups: 1) Natural immunity (unvaccinated), 2) Vaccine-induced immunity (vaccinated individuals without a COVID-19 history), and 3) Natural immunity + vaccine-induced immunity. These groups were matched by age and gender. We assessed the ability of individuals' serum to neutralize the Delta variant and compared the results of the different groups using a neutralization test followed by plaque-forming units. Results showed that 39% of individuals' serum with a history of COVID-19 (natural immunity, Group 1) could not neutralize the Delta variant, compared to 33% in vaccinated individuals without COVID-19 (vaccine immunity, Group 2). In contrast, only 7% of vaccinated individuals with a history of COVID-19 (natural + vaccine immunities) could not neutralize the Delta variant. We concluded that the effectiveness of the Ad5-nCoV vaccine to induce neutralizing antibodies against the Delta variant is comparable to that of natural infection (61% vs. 67%). However, in individuals with both forms of immunity (Group 3), it increased to 93%. Based on these results, despite the Ad5-nCoV vaccine originally being designed as a single-dose regimen, it could be recommended that even those who have recovered from COVID-19 should consider vaccination to boost their immunity against this variant.

Tracking the immune response profiles elicited by the BNT162b2 vaccine in COVID-19 unexperienced and experienced individuals

Multiple vaccines have been approved to control COVID-19 pandemic, with Pfizer/BioNTech (BNT162b2) being widely used. We conducted a longitudinal analysis of the immune response elicited after three doses of the BNT162b2 vaccine in individuals who have previously experienced SARS-CoV-2 infection and in unexperienced ones. We conducted immunological analyses and single-cell transcriptomics of circulating T and B lymphocytes, combined to CITE-seq or LIBRA-seq, and VDJ-seq. We found that antibody levels against SARS-CoV-2 Spike, NTD and RBD from wild-type, delta and omicron VoCs show comparable dynamics in both vaccination groups, with a peak after the second dose, a decline after six months and a restoration after the booster dose. The antibody neutralization activity was maintained, with lower titers against the omicron variant. Spike-specific memory B cell response was sustained over the vaccination schedule. Clonal analysis revealed that Spike-specific B cells were polyclonal, with a partial clone conservation from natural infection to vaccination. Spike-specific T cell responses were oriented towards effector and effector memory phenotypes, with similar trends in unexperienced and experienced individuals. The CD8 T cell compartment showed a higher clonal expansion and persistence than CD4 T cells. The first two vaccinations doses tended to induce new clones rather than promoting expansion of pre-existing clones. However, we identified a fraction of Spike-specific CD8 T cell clones persisting from natural infection that were boosted by vaccination and clones specifically induced by vaccination. Collectively, our observations revealed a moderate effect of the second dose in enhancing the immune responses elicited after the first vaccination. Differently, we found that a third dose was necessary to restore comparable levels of neutralizing antibodies and Spike-specific T and B cell responses in individuals who experienced a natural SARS-CoV-2 infection.

Broadly neutralizing antibodies against emerging delta-coronaviruses

Porcine deltacoronavirus (PDCoV) spillovers were recently detected in children with acute undifferentiated febrile illness, underscoring recurrent zoonoses of divergent coronaviruses. To date, no vaccines or specific therapeutics are approved for use in humans against PDCoV. To prepare for possible future PDCoV epidemics, we isolated human spike (S)-directed monoclonal antibodies from transgenic mice and found that two of them, designated PD33 and PD41, broadly neutralized a panel of PDCoV variants. Cryo-electron microscopy structures of PD33 and PD41 in complex with the PDCoV receptor-binding domain and S ectodomain trimer provide a blueprint of the epitopes recognized by these mAbs, rationalizing their broad inhibitory activity. We show that both mAbs inhibit PDCoV by competitively interfering with host APN binding to the PDCoV receptor-binding loops, explaining the mechanism of viral neutralization. PD33 and PD41 are candidates for clinical advancement, which could be stockpiled to prepare for possible future PDCoV outbreaks.

Comparative single-cell transcriptomic profile of hybrid immunity induced by adenovirus vector-based COVID-19 vaccines

In this study, antibody response and a single-cell RNA-seq analysis were conducted on peripheral blood mononuclear cells from five different groups: naïve subjects vaccinated with AZD1222 (AZ) or Ad5-nCoV (Cso), individuals previously infected and later vaccinated (hybrid) with AZD1222 (AZ-hb) or Ad5-nCoV (Cso-hb), and those who were infected and had recovered from COVID-19 (Inf). The results showed that AZ induced more robust neutralizing antibody responses than Cso. The single-cell RNA data revealed a high frequency of memory B cells in the Cso and Cso-hb. In contrast, AZ and AZ-hb groups exhibited the highest proportion of activated naïve B cells expressing CXCR4. Transcriptomic analysis of CD4+ and CD8+ T cells demonstrated a heterogeneous response following vaccination, hybrid immunity, or natural infection. However, a single dose of Ad5-nCoV was sufficient to strongly activate CD4+ T cells (naïve and memory) expressing ANX1 and FOS, similar to the hybrid response observed with AZ. An interesting finding was the robust activation of a subset of CD8+ T cells expressing GZMB, GZMH, and IFNG genes in the Cso-hb group. Our findings suggest that both vaccines effectively stimulated the cellular immune response; however, the Ad5-nCoV induced a more robust CD8+ T-cell response in previously infected individuals.

Protein nanoparticle vaccines induce potent neutralizing antibody responses against MERS-CoV

Middle East respiratory syndrome coronavirus (MERS-CoV) is a zoonotic betacoronavirus that causes severe and often lethal respiratory illness in humans. The MERS-CoV spike (S) protein is the viral fusogen and the target of neutralizing antibodies, and has therefore been the focus of vaccine design efforts. Currently there are no licensed vaccines against MERS-CoV and only a few candidates have advanced to Phase I clinical trials. Here we developed MERS-CoV vaccines utilizing a computationally designed protein nanoparticle platform that has generated safe and immunogenic vaccines against various enveloped viruses, including a licensed vaccine for SARS-CoV-2. Two-component protein nanoparticles displaying MERS-CoV S-derived antigens induced robust neutralizing antibody responses and protected mice against challenge with mouse-adapted MERS-CoV. Electron microscopy polyclonal epitope mapping and serum competition assays revealed the specificities of the dominant antibody responses elicited by immunogens displaying the prefusion-stabilized S-2P trimer, receptor binding domain (RBD), or N-terminal domain (NTD). An RBD nanoparticle vaccine elicited antibodies targeting multiple non-overlapping epitopes in the RBD, whereas anti-NTD antibodies elicited by the S-2P- and NTD-based immunogens converged on a single antigenic site. Our findings demonstrate the potential of two-component nanoparticle vaccine candidates for MERS-CoV and suggest that this platform technology could be broadly applicable to betacoronavirus vaccine development.

A tetravalent bispecific antibody outperforms the combination of its parental antibodies and neutralizes diverse SARS-CoV-2 variants

The devastating impact of COVID-19 on global health shows the need to increase our pandemic preparedness. Recombinant therapeutic antibodies were successfully used to treat and protect at-risk patients from COVID-19. However, the currently circulating Omicron subvariants of SARS-CoV-2 are largely resistant to therapeutic antibodies, and novel approaches to generate broadly neutralizing antibodies are urgently needed. Here, we describe a tetravalent bispecific antibody, A7A9 TVB, which actively neutralized many SARS-CoV-2 variants of concern, including early Omicron subvariants. Interestingly, A7A9 TVB neutralized more variants at lower concentration as compared to the combination of its parental monoclonal antibodies, A7K and A9L. A7A9 also reduced the viral load of authentic Omicron BA.1 virus in infected pseudostratified primary human nasal epithelial cells. Overall, A7A9 displayed the characteristics of a potent broadly neutralizing antibody, which may be suitable for prophylactic and therapeutic applications in the clinics, thus highlighting the usefulness of an effective antibody-designing approach.

Exploring the reported adverse effects of COVID-19 vaccines among vaccinated Arab populations: a multi-national survey study

The coronavirus disease 2019 (COVID-19) pandemic has been a major challenge worldwide for the past years with high morbidity and mortality rates. While vaccination was the cornerstone to control the pandemic and disease spread, concerns regarding safety and adverse events (AEs) have been raised lately. A cross-sectional study was conducted between January 1st and January 22nd, 2022, in six Arabic countries namely Saudi Arabia, Egypt, Syria, Libya, Iraq, and Algeria. We utilized a self-administered questionnaire validated in Arabic which encompassed two main parts. The first was regarding sociodemographic data while the second was about COVID-19 vaccination history, types, doses, and experienced AEs. A multistage sampling was employed in each country, involving the random selection of three governorates from each country, followed by the selection of one urban area and one rural area from each governorate. We included the responses of 1564 participants. The most common AEs after the first and second doses were local AEs (67.9% and 46.6%, respectively) followed by bone pain and myalgia (37.6% and 31.8%, respectively). After the third dose, the most common AEs were local AEs (45.7%) and fever (32.4%). Johnson and Johnson, Sputnik Light, and Moderna vaccines showed the highest frequency of AEs. Factors associated with AEs after the first dose included an increase in age (aOR of 61-75 years compared to the 12-18 years group: 2.60, 95% CI: 1.59-4.25, p = 0.001) and male gender (OR: 0.72, 95% CI: 0.63-0.82, p < 0.001). The cumulative post-vaccination COVID-19 disease was reported with Sinovac (16.1%), Sinopharm (15.8%), and Johnson and Johnson (14.9) vaccines. History of pre-vaccination SARS-CoV-2 infection significantly increases the risk of post-vaccination COVID-19 after the first, second, and booster doses (OR: 3.09, CI: 1.9-5.07, p < 0.0001; OR: 2.56, CI: 1.89-3.47, p < 0.0001; and OR: 2.94, CI: 1.6-5.39, p = 0.0005 respectively). In conclusion, AEs were common among our participants, especially local AEs. Further extensive studies are needed to generate more generalizable data regarding the safety of different vaccines.

To be remembered: B cell memory response against SARS-CoV-2 and its variants in vaccinated and unvaccinated individuals

COVID-19 disease has plagued the world economy and affected the overall well-being and life of most of the people. Natural infection as well as vaccination leads to the development of an immune response against the pathogen. This involves the production of antibodies, which can neutralize the virus during future challenges. In addition, the development of cellular immune memory with memory B and T cells provides long-lasting protection. The longevity of the immune response has been a subject of intensive research in this field. The extent of immunity conferred by different forms of vaccination or natural infections remained debatable for long. Hence, understanding the effectiveness of these responses among different groups of people can assist government organizations in making informed policy decisions. In this article, based on the publicly available data, we have reviewed the memory response generated by some of the vaccines against SARS-CoV-2 and its variants, particularly B cell memory in different groups of individuals.

B-cell and antibody responses to SARS-CoV-2: infection, vaccination, and hybrid immunity

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in 2019 prompted scientific, medical, and biotech communities to investigate infection- and vaccine-induced immune responses in the context of this pathogen. B-cell and antibody responses are at the center of these investigations, as neutralizing antibodies (nAbs) are an important correlate of protection (COP) from infection and the primary target of SARS-CoV-2 vaccine modalities. In addition to absolute levels, nAb longevity, neutralization breadth, immunoglobulin isotype and subtype composition, and presence at mucosal sites have become important topics for scientists and health policy makers. The recent pandemic was and still is a unique setting in which to study de novo and memory B-cell (MBC) and antibody responses in the dynamic interplay of infection- and vaccine-induced immunity. It also provided an opportunity to explore new vaccine platforms, such as mRNA or adenoviral vector vaccines, in unprecedented cohort sizes. Combined with the technological advances of recent years, this situation has provided detailed mechanistic insights into the development of B-cell and antibody responses but also revealed some unexpected findings. In this review, we summarize the key findings of the last 2.5 years regarding infection- and vaccine-induced B-cell immunity, which we believe are of significant value not only in the context of SARS-CoV-2 but also for future vaccination approaches in endemic and pandemic settings.

Sustained S-IgG and S-IgA antibodies to Moderna's mRNA-1273 vaccine in a Sub-Saharan African cohort suggests need for booster timing reconsiderations

Introduction

This study sought to elucidate the long-term antibody responses to the Moderna mRNA-1273 COVID-19 vaccine within a Ugandan cohort, aiming to contribute to the sparse data on m-RNA vaccine immunogenicity in Sub-Saharan Africa.

Methods

We tracked the development and persistence of the elicited antibodies in 19 participants aged 18 to 67, who received two doses of the mRNA-1273 vaccine. A validated enzyme-linked immunosorbent assay (ELISA) was used to quantify SARS-CoV-2-specific IgG, IgM, and IgA antibodies against the spike (S) and nucleoproteins (N). The study's temporal scope extended from the baseline to one year, capturing immediate and long-term immune responses. Statistical analyses were performed using the Wilcoxon test to evaluate changes in antibody levels across predetermined intervals with the Hochberg correction for multiple comparisons.

Results

Our results showed a significant initial rise in spike-directed IgG (S-IgG) and spike-directed IgA (S-IgA) levels, which remained elevated for the duration of the study. The S-IgG concentrations peaked 14 days afterboosting, while spike-directed IgM (S-IgM) levels were transient, aligning with their early response role. Notably, post-booster antibody concentrations did not significantly change. Prior S-IgG status influenced the post-priming S-IgA dynamics, with baseline S-IgG positive individuals maintaining higher S-IgA responses, a difference that did not reach statistical difference post-boost. Three instances of breakthrough infections: two among participants who exhibited baseline seropositivity for S-IgG, and one in a participant initially seronegative for S-IgG.

Discussion

In conclusion, the mRNA-1273 vaccine elicited robust and persistent S-IgG and S-IgA antibody responses, particularly after the first dose, indicating potential for long-term immunity. Prior viral exposure enhances post-vaccination S-IgA responses compared to naive individuals, which aligned with the prior-naïve, post-boost. The stable antibody levels observed post-booster dose, remaining high over an extended period, with no significant secondary rise, and no difference by baseline exposure, suggest that initial vaccination may sufficiently prime the immune system for prolonged protection in this population, allowing for potential to delay booster schedules as antibody responses remained high at the time of boosting. This finding calls for a reassessment of the booster dose scheduling in this demographic.

Hybrid immunity to SARS-CoV-2 arises from serological recall of IgG antibodies distinctly imprinted by infection or vaccination

We used plasma IgG proteomics to study the molecular composition and temporal durability of polyclonal IgG antibodies triggered by ancestral SARS-CoV-2 infection, vaccination, or their combination ("hybrid immunity"). Infection, whether primary or post-vaccination, mainly triggered an anti-spike antibody response to the S2 domain, while vaccination predominantly induced anti-RBD antibodies. Immunological imprinting persisted after a secondary (hybrid) exposure, with >60% of the ensuing serological response originating from the initial antibodies generated during the first exposure. We highlight one instance where hybrid immunity arising from breakthrough infection resulted in a marked increase in the breadth and affinity of a highly abundant vaccination-elicited plasma IgG antibody, SC27. With an intrinsic binding affinity surpassing a theoretical maximum (K D < 5 pM), SC27 demonstrated potent neutralization of various SARS-CoV-2 variants and SARS-like zoonotic viruses (IC 50 ∼0.1-1.75 nM) and provided robust protection in vivo . Cryo-EM structural analysis unveiled that SC27 binds to the RBD class 1/4 epitope, with both VH and VL significantly contributing to the binding interface. These findings suggest that exceptionally broad and potent antibodies can be prevalent in plasma and can largely dictate the nature of serological neutralization.

HIGHLIGHTS

▪ Infection and vaccination elicit unique IgG antibody profiles at the molecular level▪ Immunological imprinting varies between infection (S2/NTD) and vaccination (RBD)▪ Hybrid immunity maintains the imprint of first infection or first vaccination▪ Hybrid immune IgG plasma mAbs have superior neutralization potency and breadth.

Humoral and Cellular Immune Response after Three Doses of Sinopharm [Vero Cell]-Inactivated COVID-19 Vaccine in Combination with SARS-CoV-2 Infection Leads to Hybrid Immunity

BACKGROUND

Several vaccines against COVID-19 have been developed and licensed to enhance the immune response against SARS-CoV-2. Similarly, previous infection with SARS-CoV-2 has been shown to provide significant protection against severe infection and hospitalization.

METHODS

We investigated the effect of three doses of the Sinopharm vaccine and SARS-CoV-2 infection on the specific immune response in 103 volunteers, measuring neutralizing antibodies, anti-S1 IgG, anti-RBD IgM, anti-N IgM, anti-N IgG antibodies, and INF γ.

RESULTS

Our results showed that the presence of cardiovascular diseases increased the level of anti-N-IgG antibodies, while endocrinological diseases decreased the level of neutralizing antibodies and anti-N IgG antibodies, suggesting that these diseases alter the effect of vaccine-induced immunity. In addition, there was a significant decrease in anti-S1 IgG levels at 6 months and in anti-N IgG levels 18 months post-infection, while neutralizing antibodies and INF γ levels were constant at 3, 6, and 18 months post-infection.

CONCLUSIONS

Our results confirm the emergence of hybrid immunity, which is the strongest and most durable compared to natural immunity or vaccine-induced immunity. Significant positive correlations were found between humoral and cellular immunity markers: neutralizing antibodies, anti-S1 IgG and anti-N IgG antibodies, and INF γ, indicating a unique coordinated response specific to COVID-19.

Humoral and cell-mediated immune responses in HIV-vertically infected young patients after three doses of the BNT162b2 mRNA SARS-CoV-2 vaccine

Background

Data on the efficacy of three SARS-CoV-2 mRNA BNT162b2 vaccine doses and the role of previous SARS-CoV-2-infection in enhancing vaccine immunogenicity in HIV-vertically-infected people living with HIV (PLWH) are limited, as is the duration of vaccine-induced responses.

Methods

SARS-CoV-2 plasma neutralizing activity (NA) against the European (B.1), Delta (B.1.617.2) and Omicron (B.1.1.529) variants and cell-mediated immunity (CMI) were analyzed in 29 ART-treated young PLWH (mean age 27.9 years) and 30 healthy controls (HC) who received three BNT162b2 vaccine doses. Individuals were stratified based on the presence/absence of previous SARS-CoV-2 infection (infected and vaccinated -SIV-; uninfected and vaccinated -SV-). Analyses were performed before vaccination (T0), 25 days from the second dose (T1), the day the third dose was administered (T2), and 3 months after the third dose (T3).

Results

In PLWH: i) NA against all variants was higher in SIV compared to SV at T2 and was increased at T3; ii) switched-memory plasmablasts were augmented in SIV alone at T2 and T3; iii) a SARS-CoV-2 specific T cell memory was generated; iv) IFN-γ-secreting CD4+ and CD8+ T lymphocytes were boosted at T3 mainly in SV. CMI magnitude was reduced in PLWH compared to HC. Notably, after the third dose of vaccine viremia was unmodified, but CD4 T cell counts were reduced>20% in 3/29 PHLW.

Conclusion

A third dose of BNT162b2 vaccine induces strong humoral and CMI responses in young ART-treated PLWH independently from a previous SARS-CoV-2 natural infection. The lower magnitude of CMI responses should be considered when planning mRNA vaccine booster doses in PLWH.

Magnitude and Durability of the Antibody Response to mRNA-Based Vaccination Among SARS-CoV-2 Seronegative and Seropositive Health Care Personnel

Few studies have described changes in SARS-CoV-2 antibody levels in response to infection and vaccination at frequent intervals and over extended follow-up periods. The purpose of this study was to assess changes in SARS-CoV-2-specific antibody responses among a prospective cohort of health care personnel over 18 months with up to 22 samples per person. Antibody levels and live virus neutralization were measured before and after mRNA-based vaccination with results stratified by (1) SARS-CoV-2 infection status prior to initial vaccination and (2) SARS-CoV-2 infection at any point during follow-up. We found that the antibody response to the first dose was almost 2-fold higher in individuals who were seropositive prior to vaccination, although neutralization titers were more variable. The antibody response induced by vaccination appeared to wane over time but generally persisted for 8 to 9 months, and those who were infected at any point during the study had slightly higher antibody levels over time vs those who remained uninfected. These findings underscore the need to account for SARS-CoV-2 natural infection as a modifier of vaccine responses, and they highlight the importance of frequent testing of longitudinal antibody titers over time. Together, our results provide a clearer understanding of the trajectories of antibody response among vaccinated individuals with and without prior SARS-CoV-2 infection.